# How often will the same date be on the same day of the week?

Is there any pattern in this (e.g. Once per five years)?
Is it a sliding window?

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It's more complicated than that due to leap years among other things. Check out J.H. Conway's Doomsday rule where all your questions should be answered in full detail. – t.b. Apr 16 '11 at 8:09
@Theo Buehler Thanks. Post as an answer and I will accept. I thought it wouldn't be so simple. – basarat Apr 16 '11 at 8:20

Mostly, in cycles of 6, 11, and 11 years. Leap years only repeat every 28 years. See http://wiki.answers.com/Q/How_often_in_years_do_calendars_repeat_with_the_same_day-date_combinations

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+1 thank you very much. Just what I was looking for – basarat Apr 17 '11 at 6:05

All depends on the year it starts first birthday after you been born. If your birthday starts on same day , same date, same month. It will take 5 years, 6 years or 11 years which will bring you to your original day of birthday and the sequence never change. Sequence (11 6 5 6 11 6 5 6 11) all depends on which years sequence(5 6 11 6 5 6 11 6 5)or(6 5 6 11 6 5 6 11 6) you start your sequence, but it never change.You can test it yourself and see the consistency of the sequence birthday, same day of the week.

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I found out: It is a sequence like this every 11-6-5-6-11 years (periodic), 11-6-5-11 years.

Dio Stavroulias

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It's more complicated than that due to leap years among other things. Check out J.H. Conway's doomsday rule where all your questions should be answered in full detail.