What day of the week will May 12, 2037 be? What day of the week was September 17, 1004? Here is a neat algorithm that will tell you: [NOTE:- All divisions, except where noted otherwise, are integer divisions, in which remainders are discarded.] First figure out the values for "a", "y" and "m"-- variables to be plugged into a formula. a = (14 - month)/12 [month = Number of month, 1 for Jan, 2 for Feb, etc...] y = year - a [year = the 4-digit year] m = month + 12a - 2 Next, plug the values of "y" and "m" into the following formula to calculate the day: d = (day + y + y/4 - y/100 + 31m/12) mod 7 [mod 7 means modulo. "That is, take the remainder instead of your quotient as your answer (when divided by 7, in this case.!). For example, 20 mod 3 = 2, because the remainder is 2.] The answer you get for "d" will correspond to a day of the week such as: 0 = Sunday. 1 = Monday. 2 = Tuesday. 3 = wednesday. 4 = Thursday. 5 = Friday. 6 = saturday. Let's work an example, shall we? What day of the week will April 5, 2020 fall on? First figure out "a", "y" and "m": a = (14 - 4)/12 = 0 [Remember, it is integer division so remainders are discarded. 4 represents the month of April since it's the fourth month of the year.] y = 2020 - 0 m = 4 + 12(0) - 2 = 2 Now plug "y" and "m" into the "d" formula to calculate the day: d = (5 + 2020 + 2020/4 - 2020/100 + 2020/400 + 31(2)/12) mod 7 d = (5 + 2020 + 505 - 20 + 5 + 5) mod 7 d = 2520 mod 7 d = 0 [ 2520/7 = 360 with a remainder of 0] Recall from above that 0 = SUNDAY. So April 5, 2020 will be a Sunday. Remember, you can do this for dates in the past as well. If you need any help in understanding the above algorithm, please E-Mail me (given below)