5 ways to calculate the day of the week - wikihow

8/13/2019 5 Ways to Calculate the Day of the Week - WikiHow

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Ho w to Calculate the Day o f the Week

We've all heard of a few very gifted people who cancalculate in their heads, quickly (i.e., in less than 2seconds) and precisely, the day of the week for anydate. Here are several different ways to make thiscalculation.

1 Steps1.1 Method 11.2 Method 21.3 Method 3

1.4 Method 41.5 Method 5

2 Tips3 Warnings4 Related wikiHows5 Sources and Citations6 Related wikiHows

Method 1

Add the Day and the value for the Month (from the Month-Table) . If the resultingnumber is greater than 6, subtract the highest multiple of 7 in it. Hold this number till step 3.

Subtract from the (last two digits of the) Year the highest multiple of 28 in it . Addto the resulting number the number you get when you divide it by 4 and round down (i.e.,drop the decimal). Now add the value for the Century from the Century Table. If the Month

Contents

Steps
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|85 57 29 01| G | B | D | F ||86 58 30 02| F | A | C | E ||87 59 31 03| E | G | B | D ||88 60 32 04| DC | FE | AG | CB ||-----------+----+----+----+----||89 61 33 05| B | D | F | A ||90 62 34 06| A | C | E | G ||91 63 35 07| G | B | D | F ||92 64 36 08| FE | AG | CB | ED ||-----------+----+----+----+----||93 65 37 09| D | F | A | C ||94 66 38 10| C | E | G | B ||95 67 39 11| B | D | F | A ||96 68 40 12| AG | CB | ED | GF ||-----------+----+----+----+----|

|97 69 41 13| F | A | C | E ||98 70 42 14| E | G | B | D ||99 71 43 15| D | F | A | C || 72 44 16| CB | ED | GF | BA ||-----------+----+----+----+----|| 73 45 17| A | C | E | G || 74 46 18| G | B | D | F || 75 47 19| F | A | C | E || 76 48 20| ED | GF | BA | DC ||-----------+----+----+----+----|| 77 49 21| C | E | G | B || 78 50 22| B | D | F | A || 79 51 23| A | C | E | G || 80 52 24| GF | BA | DC | FE ||-----------+----+----+----+----|| 81 53 25| E | G | B | D || 82 54 26| D | F | A | C || 83 55 27| C | E | G | B || 84 56 28| BA | DC | FE | AG |'-----------+----+----+----+----|. |1600|1700|1800|1900|. |2000|2100|2200|2300|. '----'----'----'----'

3. Put these together to find the day of the week of any date. For an example, let's try June 4,2007. The year 2007 is G. We see from the day table that June 3 is G and therefore a Sunday. Butwe wanted to know about June 4. June 4 is the day after June 3. Therefore, June 4, 2007, is aMonday.

Method 4

The algorithm used in this guide is based heavily on the Doomsday Algorithm, which is easy-to-use(requiring only knowledge of addition, subtraction, multiplication, and division), requires very littlememorization, and can be extraordinarily fast with practice. The Doomsday Algorithm wasdeveloped over the course of many years by John Horton Conway [1] , a renowned mathematicsprofessor at Princeton University, who took up day-of-the-week calculation as a hobby. At the timethat he taught me the algorithm, he could calculate the day of the week in his head for ANY date onthe Gregorian calendar in 3 seconds flat. Watch this performance by Arthur Art T. Benjamin [2] ,the Mathemagician and a math professor at Harvey Mudd College, if you doubt that the algorithmcan be preformed this quickly:http://www.ted.com/index.php/talks/arthur_benjamin_does_mathemagic.html . Day-of-the-weekcalculation is one of his later mathemagic tricks. While Ive never met anyone who is that fast after first learning the algorithm, you can drastically improve your speed with practice. The Doomsday

Algorithm relies on a branch of mathematics known as modular arithmetic [3] . The algorithm onlyworks for the Gregorian Calendar, but similar tricks could be developed for any calendar system.This guide does not assume a mathematical background; for those with more mathematicalsophistication the Wikipedia article entitled Doomsday rule [4] and the Advanced Tricks for Greater Speed section of this guide would be more appropriate. There are lots of examplesthroughout the guide intended to clarify various aspects of the algorithm; feel free to skip them if you already understand the concepts they illustrate. All of the days of the week mentioned in theexamples are cor rect, but you shouldnt worry if you dont know how they were calculated whilereading the guide for the first time. There is also some deliberate repetition to hammer in some of the subtler concepts that you may wish to skim over if you already understand them.

First, here are some useful properties of

The Gregorian Calendar [5]

Years

Years divisible by 4 are leap years,with the exception that years divisible by 100 are NOT leap years,

with the exception that years divisible by 400 ARE leap years.

Non-leap years will be referred to throughout the guide as normal years. TheGregorian calendar repeats exactly every 400 years. Note that the Gregorian calendar has been reformed in the past and that this algorithm only applies to the Gregoriancalendar in its most recent state. For more information on this reform and itsconsequences for calculating the day of the week, refer to the Julian calendar sectionof the Wikipedia article entitled Doomsday rule:http://en.wikipedia.org/wiki/Doomsday_rule#Julian_calendar .

In this guide, the notation C.E. and B.C.E. will be used. C.E. means Common Eraand is equivalent to A.D. B.C.E. means Before the Common Era and is equivalent toB.C. For more information refer to the Wikipedia article entitled Common Era:http://en.wikipedia.org/wiki/Common_Era . Think of C.E. years as positive and B.C.E.years as negative (but subtract one from them first). For example, think of 1670 C.E. as1670, but think of 1540 B.C.E. as -1539. Note that there is no year 0 in the Gregorian

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calendar, so you must subtract 1 from 1540 before placing a negative sign in front of it.For a more detailed explanation, see the Wikipedia article entitled Astronomical year numbering: http://en.wikipedia.org/wiki/Astronomical_year_numbering .

In this guide, the formats mm/dd and mm/dd/yyyy will be used to represent dates incompact form. For example, 8/6 is equivalent to August 6th, 7/24/1670 is equivalent toJuly 24th, 1670 C.E., 12/6/534 is equivalent to December 6th, 534 C.E., and10/23/-1889 is equivalent to October 23rd, 1890 B.C.E.

Months

January, March, May, July, August, October, and December have 31 days. April, June,September, and November have 30 days. February has 28 days dur ing a normal year and 29 days during a leap year. Leap day, that is, the day that only exists during a leapyear, is February 29. There is a useful mnemonic to distinguish between months with 31days and fewer than 31 days. Hold out your right hand. Tap the knuckle of your indexfinger and say January. Tap the gap/dip/valley between the knuckles of your index andmiddle fingers and say February. You can remember that January has more days thanFebruary because your knuckle is taller than the gap. Next tap the knuckle of your middle finger and say March. Notice as you continue that all of the months with 31 daysare on knuckles, while all of the months with fewer days are in gaps. Youre probablywondering: What do I do once I get to July? because July is on the knuckle of your pinky. Just go back to the beginning; tap the knuckle of your index finger again and sayAugust. Continue from here to get to the rest of the months.

Days

In ANY given year (even a leap year), Doomsdays are all on the same day of the week.Here are some easy-to-remember Doomsdays: 4/4, 8/8, 10/10, 12/12, 5/9, 9/5, 7/11,and 11/7. A mnemonic for the last four Doomsdays in the list is: 9 to 5 job at a 7-11 gasstation. For example, in the year 2000, April 4, June 6, July 11, and November 7 are allTuesdays. (Important note: this does NOT mean that April 4, 2001 was also Tuesday.

April 4, 2001 was actually a Wednesday.) You can add or subtr act 7 from any

Doomsday to get another Doomsday. For example, 5/9, 5/16, and 5/23 are allDoomsdays. You dont have to just add or subtract 7 at a time though; you can use anymultiple of 7. For example, 9/5 and 9/26 are both Doomsdays, because 5+7*3 26.

Another easy-to-remember Doomsday is 3/0. No this is not a typo; 3/0 is simply another way of thinking about the last day of February. Unlike 2/28 or 2/29, 3/0 is ALWAYS thelast day of February, regardless of whether or not it is a leap year. We can even think of months as having negative days. For example, 8/8 and 8/- 6 are both Doomsdays. Toconvert 8/-6 into a normal date, simply add the number of days in the 7th month(August). Use the knuckle trick from the previous paragraph to determine that there are31 days in August. So, 8/-6 is the same as 7/25, because -6+31 25. We may also thinkof months as having days greater than 31. For example, 10/10 and 10/34 are bothDoomsdays. To convert 10/34 into a normal date, simply subtract the number of days inthe 10th month (October). Our knuckles tell us that October has 31 days, so 10/34 is11/3, because 34-31 3. We can even write June days as March days. For example, 6/6and 6/-64 are Doomsdays. May (month 5) has 31 days, so 6/-64 5/-33. April (month 4)has 30 days, so 5/-33 4/-3. March (month 3) has 31 days, so 4/-3 3/28. Thus, June-64th is equivalent to March 28th, which is a Doomsday. Be careful to account for leap

years when using these tricks to determine Doomsdays in January or February. For example, in ANY year, 3/0 and 3/-14 are both Doomsdays, but in a leap year Febr uaryhas 29 days, so 3/-14 2/15, while in a normal year February has 28 days, so 3/-14 2/14. Thus, February 15th is a Doomsday during leap years, but February 14th is aDoomsday during normal years. You have to be careful when going from March toJanuary as well. Leap year: 3/-42 2/-13 1/18; normal year: 3/-42 2/-14 1/17.

Now that you know how the Gregorian calendar works, you can use your knowledge to

Calculate the Day of the Week in Your Head From the Year, Month, and Day

Number-days

Number-days are numbers that ar e associated with days of the week by a mnemonic.

Sunday NONEday 0Monday ONEday 1Tuesday TWOSday 2Wednesday THREESday 3 (lame, I know)Thursday FOURSday 4Friday FIVEday 5Saturday SIXAday 6Sunday SEENday 7 (seen as in a contraction for seven that sounds likesun)

Because there are seven days in a week, you can add or subtract any multiple of 7 at ANY point during ANY part of ANY day-of-the-week calculation. This is why Sunday isboth 0 and 7. Monday could be thought of as -6, 8, 71, etc. Throughout the guide youwill see (and have been seeing) congruence symbols, , rather than equals signs, =,because 71 does NOT equal 8, but they are equivalent for the purpose of determiningthe day of the week. While finding a day of the week we are only interested in theremainder when numbers are divided by 7. All of these congr uences are thus modulo7, abbreviated mod 7. Numbers are congruent modulo 7 if their remainders are thesame when they are divided by 7. This is equivalent to the earlier point that you can add

or subtract multiples of 7 as you wish. For example, 1 8, but 1 8 (mod 7). Moreexamples of the way in which modulo behave are -15 -1 6 (mod 7) and 4 -3 7004(mod 7). The notation (mod 7) will be left off throughout the guide, because allcongruences are assumed to be modulo 7.

If you know that August 8, 1953 is a Saturday, then you can quickly determine that August 4, 1953 is a Tuesday, because four days before SIXAday is TWOSday. That is,6-4 2. Likewise, if you know that 9/5/1776 is a FOURSday, then you can quickly seethat 9/7/1776 is a SIXAday, because 7-5 2 and 4+2 6. Remember that you can add
http://en.wikipedia.org/wiki/Astronomical_year_numbering


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or subtract any multiple of 7 to a Number-day. If you know that 10/10/-2543 is a SIXAday,then you can quickly determine that 10/2/-2543 is a FIVEday, because 2-10 -8 -8+7 -1, and 6+(-1) 5. Once again, remember to watch out for leap years, like 18,400. If you know that 2/28/18,400 is a ONEday, then you can quickly deter mine that 3/3/18,400is a FIVEday, because 2/28/18,400 3/-1/18,400 and 3-(-1) 4 and 1+4 5.

Definitions of Year-days and Century-days

The Year-day of any given year is the day of the week on which all of its Doomsdayslie. For example, every Doomsday in 2009 is a Saturday, so the Year-day of 2009 isSaturday. The Century-day of any given century is the Year-day of the first year of the century. The Century-year is the first year of any given century. The Year-day of 1900 is Wednesday, so the Century-day of the 1900s (i.e. the 20th century) isWednesday. Also, 1900 is the Century-year of the 20th century. Note though, that the

Century-year of the century that -1362 lies in (i.e. the -1300s or the 14th century B.C.E.)is -1400, NOT -1300, because -1400 comes before -1300. Remember also that -1400 isequivalent to 1401 B.C.E., NOT 1400 B.C.E.

Calculating Big Tuesdays (400 Years)

The Year-day of every year divisible by 400 is Tuesday. These Year-days are calledBig Tuesdays (just to help you remember them). Years that are divisible by 400 arecalled Big Tuesday-years, and centuries that have Century-days that are also BigTuesdays are called Big Tuesday-centuries. Thus, the Year-day of 1600 is a BigTuesday. The Century-days of the 2000s, the -4400s, and the 96,812,000s are all BigTuesdays, the 2000s, the -4400s, and 96,812,000s are all Big Tuesday-centuries, and2000, -4400, and 96,812,000 are all Big Tuesday-years.

Calculating Century-days (100 Years)

If you are NOT in a Big Tuesday-century, then you can find the Century-day as follows.Subtract 100 from the Century-year until you get to a Big Tuesday-year. Count howmany times you subtracted 100. If you subtracted 100 once, then the Century-day isSunday; if twice, then its Friday; if thrice, then its Wednesday; if four or more times,

then you messed up, because one of every four Century-years is a Big Tuesday-year.For example, the Century-day of the 1800s is Friday, because you subtract 100 twice toget 1600, which is a Big Tuesday-year (because its divisible by 400). The pattern lookslike this: 1600 TWOSday 2, 1700 SUNday 0, 1800 FIVEday 5 -2, 1900 THREESday 3 -4, 2000 TWOSday 2 -5, and so on. Note that you can get fromone Century-day day to the next by subtracting two from the initial Century-day. Thisonly works when the larger of the two adjacent centuries is NOT a Big Tuesday-century.Thats fine though, because you already know that the Century-day of every BigTuesday-century is TWOSday.

Calculating Dozen-days (12 Years)

The Dozen-year of any given year is the largest year that is both less than or equal tothe given year and that has the property that the positive difference of itself and theCentury-year is divisible by 12. The Dozen-day of any given year is the Year-day of the Dozen-year. The Dozen-day can be calculated by adding the Century-day to theresult of the division by 12. For example, the Dozen-year of 1234 is 1224, because1224-1200 24 12*2, and no larger years that are still less than or equal to 1234 yield

a positive difference with 1200 that is divisible by 12. Since the Year-day of 1224 isThursday, the Dozen-day of 1234 is also Thursday. Note that the Dozen-days for 1235,1226, and 1229 ar e all Thursdays as well; while the Dozen-days for 1236 and 1238 arenot the same (they are, in fact, Fridays). For another example, we can calculate theDozen-day of -1713. We first need to find the Century-day of the -1700s. Since we mustsubtract 100 three times from -1700 to arrive at a Big Tuesday-year, the Century-day isTHREESday. Next we must find the Dozen-year. Note that the Dozen-year is NOT -1712,but rather -1716, because -1716-(-1800) = 84 = 12*7. So, the Dozen-day of -1713 is3+7 3 THREESday (since we can subtract 7 as we please).

Calculating Quad-days (4 Years)

The Quad-year of any given year is the greatest number that is both less than or equalto the given year and divisible by 4. The Quad-day of any given year is the Year-dayof the Quad-year. For example, the Quad-year of 1620 is 1620; while that of 1643 is1640. The Quad-days of 1640, 1641, 1642, and 1643 are all Wednesday; while theQuad-day of 1620 is Saturday. We can calculate the Quad-day as follows. If the givenyear is 1642, then the Dozen-year is 1636, because 1636-1600 12*3. The Century-year, 1600, is a Big TWOSday. 3+2 5, so the Dozen-day of 1642 is FIVEday. Subtract4 from the Quad-year, 1640, until you get to the Dozen-year. Multiply the number of times you subtracted 4 by -2, and add this result to the Dozen-day to get the Quad-day.In our example, 1640-4*1 1636, 1*-2 -2, and 5+(-2) 3, so the Quad-day of 1642 isWednesday (as mentioned previously). Wednesday, is thus also the Year-day of 1640.

Calculating Year-days (1 Year)

If the given year is NOT divisible by 4, like 1642, then subtract the Quad-year from thegiven year. Add the result to the Quad-day to get the Year-day. In our example, 1642-1640 2, and 2+THREESday FIVEday, so the Year-day of 1642 is Friday.

Calculating Doomsdays (Months and Days)

Once you know the Year-day, you know the day of the week of every Doomsday in thatyear. For example, if the date were 9/5/1642, you would already know that it was aFriday. If the date were 6/20/1642, then you would subtract 7 days twice to discover that6/20/1642 is the same day of the week as 6/6/1642, which is a known Doomsday. Thismeans that 6/20/1642 is also a Doomsday, and is therefore a Friday.

Calculating Days of the Week (Days)

If youre given a date like 4/20/1642, which is NOT a Doomsday, then simply find thenearest Doomsday by repeatedly adding or subtracting 7 to known Doomsdays. Weknow 4/4/1642 is a Doomsday, so we add 14 days to discover that 4/18/1642 is aDoomsday. Now we know that 4/18/1642 is a FIVEday, so we simply add 2 days to findthat 4/20/1642 is a SEENday. Dont forget that the nearest known Doomsday may notbe in the same month. For example, 3/29/1642 is closer to 4/4/1642 than to 3/0/1642.Since 4/4/1642 4/-3/1642 3/28/1642, we know that 3/29/1642 FIVEday + 1 SIXAday.


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Method 5

This is similar to method 1, but for me, it is faster.

Memorize this:

Use this table to know the values of the days:

0 Saturday 1 Sunday 2 Monday 3 Tuesday 4 Wednesday 5 Thursday 6 Friday (7 Saturday)

And remember that in mod 7 the numbers 1, 8, 15, 22, and 29 ar e equal

Use this table to know the values of the months.

Jan Feb Mar 0 3 3 Apr May Jun 6 1 4 Jul Aug Sep 6 2 5 Oct Nov Dec 0 3 5

Use this table to know the values of the years.

(come back to this later if it does not make sense now)

0-2345- 0 0123-56 5 01-3456 11 -1234-6 17 012-456 22

The years, taken at ten-year intervals, fall into a pattern. Read down the columns to see thepattern. Note that the top row of the chart does not fit the pattern.

. ,----,----,----,----,

. |1600|1700|1800|1900|

. |2000|2100|2200|2300|

. ,----+----+----+----+----|

. | 00 | BA | C | E | G |

. |----+----+----+----+----|

. / 10 / C / E / G / B /

. | 20 | ED | GF | BA | DC |

. / 30 / F / A / C / E /

. | 40 | AG | CB | ED | GF |

. / 50 / B / D / F / A /

. | 60 | DC | FE | AG | CB |

. / 70 / E / G / B / D /

. | 80 | GF | BA | DC | FE |

. | 90 | A | C | E | G |

. '----'----'----'----'----'

. |1600|1700|1800|1900|

. |2000|2100|2200|2300|

. '----'----'----'----'

The Century Table repeats itself every 400 years in the 0-5-3-1 pattern shown in the table.

Memorize the following: 4/4, 6/6, 8/8, 10/10, 12/12 and 7/11, 11/7, 5/9, 9/5 and 1/31, 2/7-14-21-28, 3/7-14-21-28.

You have to also remember "2007 Wednesday" or some other nearby year. You can nowcalculate any day-of-week within a decade or so.

To calculate day-of-week for years farther away (say 1970 or 1900 or 1800) it might help tomemorize key years and the base day of that year, rather than counting from2007/Wednesday back to 1800 (don't forget leap years).

The first row of the table for days can be memorized as "Add G, beg C, fad F". Once you knowthe first row, count forward to find the rest of the days.

Memorize "1-8-15-22-29". Whatever the letter for the 1st of the month is, it will be the same for the 8th, 15th, 22nd, and (if the month has at least 29 days) the 29th.

Tips

Warnings


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This algorithm works for the Gregorian Calendar. This is used in the US after 1752 (after theBritish took it up) but in some countries it was taken up earlier (Spain and Portugal). Russiaonly adopted it after the Russian Revolution. So you should always ask the question 'WhatCountry'?' before performing the algorithm for completeness.

Do not try to go too fast at first. Concentrate on being precise first before you concentrate onspeed. Build up your speed over time. Going too fast is the surest way to make mistakes andthen the process is no fun. For instance, it seems that 20 percent of the people know the dayof the week they were born on, so there will often be someone around to check out if you arecorrect.

Watch out for people who may give you dates that do not exist just to trick you, e.g., April 31st(there aren't 31 days in April) or February 29, 1900 (this turn of the century year is not a leapyear).

You will get discouraged at first when you're not having much luck progressing. Don't give up,though. Success will gradually come.

Some wise guys will get jealous that you are attracting all the attention with your "party tr ick"and say something like, "Oh, that's no big thing. Idiot (autistic) savants can do that." So itmight be a good idea to pr epare in advance some quick comeback like, "You know, you'reabsolutely right, they can. But what they can do is perhaps one more thing than you canobviously do."

If you practice enough, you will eventually memorize more Doomsdays and all of the commonCentury-days (like 1900s 3 and 2000s 2). Once you can get the answer right in your headfairly quickly, you can impress your friends by telling them the day of the week that they or some famous person were born on. One of the easiest ways to increase your speed is tomemorize all of the numbers associated with the months of the year (if you havent already),so you dont have to waste time counting from January. Another quick way to increase your

speed is to memorize some January and February Doomsdays for non- leap years, like 1/10and 2/0. You can add one to any January or February non-leap year Doomsday to get theDoomsday for a a leap year. So, 1/11 and 2/1 would be the leap year Doomsdays. For a tableof all of the Doomsdays, refer to the Overview of all Doomsdays section of the Wikipediaarticle entitled, Doomsday rule:http://en.wikipedia.org/wiki/Doomsday_rule#Overview_of_all_Doomsdays .

It is useful to know the effect that adding different numbers of years will have on the Year-day.Because of leap years, these tricks only work within certain blocks of a cer tain number of years and only when you begin on the first year in the block. As mentioned in the CalculatingCentury-days section, within standard 400-year blocks (i.e. 1600-1699 or 1200-1599, butnot 1400-1799), beginning from any Big Tuesday-year (i.e. 1600 or 1200), adding 100 yearssubtracts 2 from the day of the week. Within standard 100-year blocks (i.e. 1700-1799 butnot 1704-1803), beginning from any Quad-year (i.e. 1700 or 1764), adding 4 years subtracts2 from the day of the week, adding 12 years adds 1 to the day of the week, adding 16 yearssubtracts 1 from the day of the week, and adding 28, 56, and 84 years adds 0 to (i.e. does notaffect) the day of the week.

You can work backwards instead of forwards from Big Tuesday-years by adding one to BigTuesday to get that the Century-day of the century before a Big Tuesday-century isWednesday. The best technique for Century- days is simply to memorize the simple patternthat they follow, which repeats every 4 centuries: 2, 0 or 7, -2 or 5, 3. You can also workbackwards from Dozen-years and Quad-years. To get to the Year-day of a year immediatelypreceding a leap year, subtract two from the Year-day of the leap year. Dozen-years andQuad-years are leap years (UNLESS they are also Century-years, excluding the cases inwhich they are also Big Tuesday-years, when they ARE leap years). To get to the Year-day of a year immediately preceding a normal year, subtract one from Year-day of the (larger)normal year. With more practice, you could quickly find the day of the week for a morechallenging date, say January 16, 6387228 B.C.E. See the next paragraph for the solution.

First of all, remember to convert from B.C.E. into negative years (i.e. astronomical year numbering) to get 1/16/ -6,387,227. Now, we notice that we can ignore any digits after the f irst4, because the Gregorian calendar repeats every 400 years (and, thus, also every 10,000years). Thus, 1/16/-6,387,227 1/16/-7227. Now, we notice that -7600 is a Big Tuesday-year,but in this case it would be easier to work backwards from -7200, which is also a Big Tuesday-year. The Century-year, -7300, is one century before a Big Tuesday-century, so the Century-day is THREESday. We can add 84 years without affecting the day of the week to get that-7216 is a THREESday. We can subtract 12 years, reducing the day of the week by 1, to get-7228 is a TWOSday. We can add 1 year, adding 1 to the day of the week, to get that -7227is a THREESday. Since, -7227 is NOT divisible by 4 it cannot be a leap year, and thus 1/10 isa Doomsday. Now, we know that 1/10 1/17 1/16 + 1, so we subtract one from the Year-day, THREESday, to get that January 16, 6387228 B.C.E. is a Tuesday.

Watch out for leap years. A leap year has two Sunday letters one for before, and one for after, February 29.

If you cant figure out why you keep getting a different answer than the Doomsday Calculator on any date B.C.E., such as number 2 from the practice quiz, dont forget to subtract one fromthe year before placing a negative sign in front of it to account for the fact that there is no year 0 in the Gregor ian calendar. For example, August 16, 1783 B.C.E. would be inputted into theDoomsday Calculator as 8/16/-1782. Also, if you still arent getting the same answer, makesure that you input the correct number for the month.

Don't get frustrated if you keep getting the answer wrong at first. If calculating the day of theweek in your head were easy, then it wouldn't be near ly so impressive once you do get itdown.
http://en.wikipedia.org/wiki/Doomsday_rule#Overview_of_all_Doomsdays


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How to Memorize DatesHow to Calculate Leap Years

Other explanations of the Doomsday Algorithm and why it works can be found at the followingURLs: http://quasar.as.utexas.edu/BillInfo/doomsday.html , http://rudy.ca/doomsday.html ,and http://www.theworldofstuff.com/other/day.html . The fir st link includes John HortonConways 4-stanza mnemonic poem to help you remember the basics of the Doomsday

Algorithm.

How to Calculate the Day of the Week in ExcelHow to Calculate in Your Head the Year when You Know the Month, Day and Day of the Week

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Sources and Citations

Related wikiHows
http://www.wikihow.com/Calculate-in-Your-Head-the-Year-when-You-Know-the-Month%2C-Day-and-Day-of-the-Weekhttp://www.wikihow.com/Calculate-the-Day-of-the-Week-in-Excelhttp://www.theworldofstuff.com/other/day.htmlhttp://rudy.ca/doomsday.htmlhttp://quasar.as.utexas.edu/BillInfo/doomsday.htmlhttp://www.wikihow.com/Calculate-Leap-Yearshttp://www.wikihow.com/Memorize-Dates

5 ways to calculate the day of the week - wikihow

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