What Day Was I Born Calculator
Enter any birth date to find your birth day, Western zodiac sign, Chinese zodiac year, birthstone, and birth flower.
Works for any date from 1900 to now.
The day of the week for any date can be calculated using Zeller’s Congruence — a mathematical algorithm that works for any date in the Gregorian calendar from 1582 onward.
Zeller’s Congruence Formula:
h = (q + floor(13(m+1)/5) + K + floor(K/4) + floor(J/4) − 2J) mod 7
Where:
- h = day of week (0=Saturday, 1=Sunday, 2=Monday … 6=Friday)
- q = day of month
- m = month (3=March, 4=April … 14=February — January and February count as months 13 and 14 of the previous year)
- K = year mod 100 (last two digits)
- J = floor(year / 100) (century)
Worked Example:
What day was July 4, 1776?
- q = 4, m = 7, year = 1776
- K = 76, J = 17
h = (4 + floor(13×8/5) + 76 + floor(76/4) + floor(17/4) − 2×17) mod 7 h = (4 + 20 + 76 + 19 + 4 − 34) mod 7 h = 89 mod 7 = 5 → Thursday
July 4, 1776 was indeed a Thursday.
Quick Mental Method (Doomsday Algorithm):
Anchor days by century:
- 1800s: Friday
- 1900s: Wednesday
- 2000s: Tuesday
Certain dates always fall on “Doomsday” for their year — then count forward or back.
Practical Tips:
- January 1 follows this pattern: advances 1 day each year, 2 days after a leap year
- For birth years 1970–2030, most people can calculate quickly using a date app — but the algorithm is the foundation
- Useful for genealogy: knowing the day helps verify historical records and family stories