How to Calculate the Day when you have the Month, Year and Day-of-Week.
Calculate Steps 1 through 3 of the Day-of-Week technique, using 0 (zero) in step 1 for the Day, then calculate Step 4, below, using the resulting (result) value from those steps.
Step 4 – Look up the known Day of the Week for the Target Date in the Day-of-Week Table. If the Result is greater than or equal to the value for the target Day-of-Week, add 7 to that target Day-of-Week value. Now subtract the Result from the adjusted Day-of-Week value. This result is the first occurrence of that Day-of-Week that month. To find the second, third, fourth and maybe fifth occurrences, add 7, 14, 21 and 28 to this result.
For an example using January 11, 1988, click here (see parts I and III only).
Another Quick Way to Calculate an Upcoming Day
Unrelated to the above formula, if the DAY you want is coming up in just a matter of a specific number of weeks or days, there is another fast way you can do this calculation. Let's say it is January 11, 1988, (a Monday) and you're in a meeting and someone says let's meet exactly four weeks from now. Well, you know that four weeks contain 28 days, so you add the 28 to today's day (11) and you get 39. But you know that January does not have 39 days in it so you subtract the 31 days in January and are left with 8. So four weeks from January 11, 1988, will be February 8th, a Monday. But if someone suggests to meet 9 weeks from January 11th, that's 63 days away, and 63 plus 11 is 74, and 74 minus 31 (January's days) is 43. But February does not have 43 days in it, so subtract the 29 days for February (remember, 1988, is a leap year) and you get March 14th, a Monday.
