Birthday Day Calculator

YYYY-MM-DD. Any date in the proleptic Gregorian calendar.
Birth-date mode: leave blank to count from today.
Day of the week
Sunday
Day of the Week Calculator
ISO weekday number (Monday = 1)
7
US weekday number (Sunday = 1)
1
Day of the year
201
Days left in the year
164 days
Days in that year
365 days
ISO week number
29
ISO week-numbering year
1,969
ISO week date
1969-W29-7
Calendar year
1,969
Quarter
3
Month
July
Day of the month
20
Leap year
no
Occurrence of that weekday in the month
3
Zeller’s congruence
q=20, m=7, K=69, J=19: (20 + floor(13*(7+1)/5)=20 + 69 + floor(69/4)=17 + floor(19/4)=4 + 5*19=95) mod 7 = 1
Summary
1969-07-20 was a Sunday, day 201 of 1969.
Worked out from ISO 8601-1:2019, Date and time - Representations for information interchange and 2 other sources.

How this is worked out

4 steps
  1. Zeller's congruence for 1969-07-20: q=20, m=7, K=69, J=19: (20 + floor(13*(7+1)/5)=20 + 69 + floor(69/4)=17 + floor(19/4)=4 + 5*19=95) mod 7 = 1, and h = 1 counts from Saturday, so the day is Sunday.
  2. Day of the year: 201 of 365 (1969 is not a leap year), leaving 164 days.
  3. ISO week date: 1969-W29-7. The week belongs to 1969 because that is the year holding its Thursday.
  4. Anniversaries are listed from 2026-09-14 forward; a common year advances the weekday by one (365 = 52*7 + 1) and a leap year by two.
Coming anniversariestable
2027-07-20: Tuesday, 2028-07-20: Thursday, 2029-07-20: Friday, 2030-07-20: Saturday, 2031-07-20: Sunday

Results are general information, not financial, tax, legal, medical or engineering advice.