Day of the Week of Any Date

Day of the Week of Any Date

     On what day of the week were you born? On what day of the week we'll be celebrating New Year 2015?

     Be a walking calendar or perform this trick as magic to amaze anyone. =)

Step 1: Assign these numbers to the days of the week:

0 = Sunday        (NONEday)

1 = Monday       (ONEday)

2 = Tuesday       (TWOsday)

3 = Wednesday (3 fingers looks W)

4 = Thursday     (FOURsday)

5 = Friday          (FIVEday)

6 = Saturday      (SIXturday)

Step 2: Remember these codes for the month (mcode).

Jan. = 6  (5 for leap year)

Feb. = 2  (1 for leap year)

Mar. = 2

Apr.  = 5

May  = 0

Jun.  = 3

Jul.   = 5

Aug. = 1

Sep. = 4

Oct.  = 6

Nov. = 2

Dec. = 4

     That is 622 503 514 624. Read it 10 times to paste in your memory. =) Month codes will be explained later.

Step 3: Year code (ycode) for 2015 is 4. Year codes will be explained later.

Step 4: Formula.

     Day = mcode + date + ycode

Example 1: January 1, 2015

                  (New Year's Day)

Day = mcode + date + ycode

Day = 6 + 1 + 4 = 11

       = 11 - 7 = 4 ***

Day = 4 = Thursday

January 1, 2015 is Thursday!

***Always reduce numbers by subtracting multiples of 7 (i.e. 7, 14, 21 & 28).

Example 2: February 14, 2015

14 - 14 = 0

Day = mcode + date + ycode

Day = 2 + 0 + 4  ***

Day = 6 = Saturday

February 14, 2015 is Saturday!

     Using year code of 4 and had memorized the month codes, you will now know what day of the week an any date in 2015 is!

     Now, you want to check your birthdate? Or any date in the past or future?

Just wait. =)

     Before we cook something, we must have to prepare the ingredients first. So, how is the formula and codes were derived?

Days:

     For any given month, all the multiple of 7 days fall on the same day of the week. If day 7 is Sunday, day 14, 21 & 28 are also Sundays. Thus, day 11 is the same with day 4  a Thursday (11-7=4). So, always reduce numbers by deducting multiples of 7 and still get the same result. In this way, you will be adding numbers not greater than 6 mentally.

Month codes (mcode):

     Start with January as 6. Next month adjustment is due to extra days from the exact 4 weeks (4x7=28). January has 31 days (31-28=3), so February dates will jump 3 days from January. (i.e. If January 1 is Thursday, February 1 will be Sunday)

Feb mcode = Jan mcode + 3

Feb mcode = 6 + 3 = 9 (- 7) = 2 ***

      February has 28 days, that's exactly 4 weeks (4x7=28), so dates in March will fall on the same days with February. (i.e. 28-28=0)

Mar mcode = Feb mcode + 0

Mar mcode = 2 + 0 = 2

And so on...

     That's how the month codes are generated. But you can easily just memorize 622 503 514 624, with exemption of 5&1 (instead of 6&2) for Jan. & Feb. respectively on leap years.

Year codes (ycode):

     A normal year consist of exactly 52 weeks (52x7=364) plus 1 day, to make 365 days. This 1 extra day makes a given date in a given month fall one day later in the next normal year. ( e.g. If January 1, 2014 is Wednesday,  January 1, 2015 will be Thursday).

     So, the year code will have plus 1 day adjustment in the next normal years.

Year codes (ycode):

     2000 = 0

     2001 = 1

     2002 = 2

     2003 = 3

     However, on leap years (366 days), everything must jump ahead 2 days after Feb. 29th. By that, the year code for 2004 (leap year) is not 4 but 5. And there is 5 & 1 mcode adjustment for Jan. and Feb respectively. The days jump by 2. Leap years happen every 4 years. Leap, jump, leapfrog, jump-start, ...hmmm whatever =)

     Let's have a walk to the year codes:

2000 = 0  (leap year)

2001 = 1

2002 = 2

2003 = 3

2004 = 5  (leap year, jump 2)

2005 = 6

2006 = 0  (6+1=7, 7-7=0)

2007 = 1

2008 = 3  (leap year, jump 2)

2009 = 4

2010 = 5

2011 = 6

2012 = 1  (leap year, 6+2=8, 8-7=1)

2013 = 2

2014 = 3

2015 = 4

2016 = 6  (leap year, jump 2)

2017 = 0  (6+1=7, 7-7=0)

2018 = 1

2019 = 2

2020 = 4 (leap year, jump 2)

2021 = 5

2022 = 6

2023 = 0  (6+1=7, 7-7=0)

2024 = 2 (leap year, jump 2)

2025 = 3

2026 = 4

2027 = 5

And so on...

     Notice the codes for 2012 and 2014, take the last 2 digits and divide by 12 and this goes until 2096.

2000 = 0

2012 = 1 = 12/12

2024 = 2 = 24/12

2036 = 3 = 36/12

2048 = 4 = 48/12

2060 = 5 = 60/12

2072 = 6 = 72/12

2084 = 0 = 7 = 84/12 (drop 7)

2096 = 1 = 8 = 96/12 (drop 7)

     Without leap years, year code pattern will repeat every 7 years. But because of the effect of leap years every 4 years, year code pattern will repeat in every 28 years.

     Meaning to say, year 2000, 2028, 2056 & 2084 have the same year codes which is 0. Example for year 2030, take 2030 minus 28 = 2002. And you know year code for 2002 is 2.

     This will work for any year. For 1900 - 1999 just add 1 for adjustment.

Example:

     Your birthday was on June 15, 1982, what day of the week is it? We know year code of 84 = 84/12 = 7 = 0. Moving backwards to 82:

leap year 84 to 83 is 7-2 = 5

Reg. year 83 to 82 is 5-1 = 4

ycode for 82 is 4 then add 1 for 1900-1999 adjustment

1982 ycode = 4+1 = 5

June 15, 1982

mcode = 3 (from 622 50[3] 514 624)

date = 15 - 14 = 1 ***

ycode = 5

Day = mcode + date + ycode

       = 3 + 1 + 5 = 9

       = 9 - 7 = 2

Day = 2 = Tuesday

June 15, 1982 is Tuesday!

     Below are the adjustments for year codes:

1600 to 1699 = add 0

1700 to 1799 = add 5

1800 to 1899 = add 3

1900 to 1999 = add 1

2000 to 2099 = add 0

2100 to 2199 = add 5

2200 to 2299 = add 3

2300 to 2399 = add 1

And so on... (0-5-3-1 pattern)

     One important note here for January and February in the years ending in 00: If a year ends in 00, apply leap year adjustment (5&1 month code) only if it is divisible by 400. The years 1600, 2000, and 2400 are divisible by 400 while the years 1700, 1800, 1900 & 2100 are not.

Tip: When performing magic trick to anyone, ask first the year. So you will have time to find the year code. Say 2014, year code of 2012 is 12/12 = 1, add 2 years, 1+2 = 3. When you already have the year code in your mind, ask for the complete date.

Say Dec. 25, 2014,

Dec mcode = 4

Date = 25 - 21 = 4 ***

2014 ycode = 3

Day = mcode + date + ycode

Day = 4 + 4 + 3 (- 7) = 4 = Thursday

Dec. 25, 2014 is... (drum rolls...) ...Thursday!!!

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