# Finding the day of the same date of previous month?

I wanted to know if there was a short way that I could determine the day which would have been for a given date.

For example, looking at the date today 4/3/17. Is there anyway we can easily determine on which Which is 4/2 would have fallen on?

I know the constraint over here is the no. of days of previous month. But still is there any shortcut/formula to overcome it?

• en.wikipedia.org/wiki/Determination_of_the_day_of_the_week – JMoravitz Mar 4 '17 at 0:01
• Also., i would caution you to specify in any question relating to dates what format you are expressing your date in, be it mm/dd/yyyy or as dd/mm/yyyy or otherwise as certain countries do it different ways. – JMoravitz Mar 4 '17 at 0:05
• Leap years make this rather bothersome for longer periods. I'd recommend using a pre-built function or library to do it unless this question is purely academic or recreational. – Alexis Olson Mar 4 '17 at 0:15

## 1 Answer

February messes things up. However, for the remaining months of the year... There are 61 days between all of the even numbered months. That is 8 weeks and 5 days. Or two days short of 9 weeks.

So, 4/4, 6/6, 8/8, 10/10, and 12/12 will all fall on the same day of the week.

The last day of February will fall on this same day of the week. And in a non-leap-year then, so will the last day of January.

this gives you enough way-points to navigate around the calendar. But, for a few more, the mnemonic "work 9 to 5 at the 7-eleven" fills in some more.

Add 7/11, 11/7, 9/5, 5/9, to the list of days that fall on the same weekday as those above.

And this doesn't matter if you write your dates MM/DD like an American or DD/MM like the rest of the world.

• Hey , Thanks but I already knew about this "doomsday" concept. Still, it doesn't answer my doubt precisely. Like ok I know the day today is 5/3/ ie wednesday. (DD-MM) How to directly determine what will the date be in 5/4.?? – pluto20010 Mar 5 '17 at 8:04
• ??????????????? – pluto20010 Jul 29 '17 at 20:46