Day of Week Calculator — Find Day for Any Date
Find what day of the week any date falls on. Works for past and future dates, showing the day name, week number, and days until the next occurrence of each weekday. See also our Date Calculator and Days Calculator.
How to Find the Day of the Week for Any Date
- Enter any date (past or future) in the input field.
- Click Calculate to find the day of the week.
- View the day name, ISO day number (1=Monday to 7=Sunday), and week number.
- See how many days until the next occurrence of each weekday.
- Use this for planning events, checking historical dates, or scheduling.
Formula
Zeller's Congruence (simplified):
h = (q + floor(13(m+1)/5) + K + floor(K/4) + floor(J/4) - 2J) mod 7
Where: q=day, m=month, K=year%100, J=floor(year/100)
ISO Week Number uses the Thursday-based week system
Example
Date: July 4, 2025
Day of Week: Friday
Day Number: 5 (ISO: Mon=1, Fri=5)
Week Number: 27
Next Monday: 3 days away
Notable Dates and Their Days
| Date | Event | Day of Week |
|---|---|---|
| Jan 1, 2025 | New Year 2025 | Wednesday |
| Jul 4, 2025 | Independence Day 2025 | Friday |
| Dec 25, 2025 | Christmas 2025 | Thursday |
| Jan 1, 2026 | New Year 2026 | Thursday |
| Jul 20, 1969 | Moon Landing | Sunday |
| Jan 1, 2000 | Y2K | Saturday |
Frequently Asked Questions
How far back can I check dates?
This calculator works for any date in the Gregorian calendar (adopted in 1582). For dates before that, the Julian calendar was used with different rules.
What is the ISO week number?
ISO 8601 defines week 1 as the week containing the first Thursday of the year. Weeks start on Monday and are numbered 1-52 (or 53).
Does the day of week repeat on a pattern?
The calendar repeats every 400 years exactly. Within that cycle, the same date falls on the same day of the week every 5, 6, or 11 years depending on leap year positions.
What day was I born on?
Enter your birth date to find out. Many people are curious about the day of the week they were born, which some cultures consider significant.
Why does the week start on different days?
In the US, weeks traditionally start on Sunday. ISO 8601 (used internationally) starts weeks on Monday. This calculator shows both numbering systems.