Doomsday Help
Enter a date and we'll show the steps needed (according to the
Doomsday Rule
) to find the corresponding day of the week.
Year
Month
Date
1. Get the Doomsday of the first year of the target century.
The Doomsday across centuries progresses -2, -2, -2, -1, ...repeating.
Sun
1700
Mon
Tue
1600
2000
Wed
1500
1900
Thu
Fri
1800
Sat
The Doomsday of 1900 is a Wednesday.
2. Divide the sub-century year by 4 to get the number of leap years between the start of the century and our target year.
69 / 4 = 17
3. Add these extra days progressed to the regular (one day) progressions for each year.
69 + 17 = 86
4. Add this progression to the Doomsday of our target century to get the Doomsday for our target year.
86 (mod 7) = 2 (mod 7)
Wednesday + 2 = Friday
The Doomsday of 1969 is Friday.
5. Determine the reference Doomsday for our target month.
For July this is 11
Remember: "7-11", this is the 7th month so it's the 11th date.
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6. Calculate the difference between our target date and this reference date.
20 - 11 = 9
7. Add this difference to the Doomsday of the year to determine the day of the week for our target.
9 (mod 7) = 2 (mod 7)
Friday + 2 = Sunday
Finished!
July 20, 1969 is a Sunday