Quick answer
The weekday follows from the day count in the Gregorian calendar. 1 March 2025 is a Saturday, the 60th day of a non-leap year.
Enter a date. The calculator returns the weekday, the day of the year and whether it is a leap year.
Related tools: Birthday Calculator: Next birthday, days until it, and your current age. Baby Age Calculator: A baby's age in weeks, months and days. Age Difference Calculator: Time between two birth dates.
How to use the Weekday Calculator
- Pick date.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Date | A calendar date | — |
Formula and method
Formula
weekday from the proleptic Gregorian calendar day count
IEEE-754 double precision; shown to at most 6 decimal places.
Uses the Gregorian calendar for all dates.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Date = 2025-03-01.
| Result | Value |
|---|---|
| Day of the week | Saturday |
| Day of the year | 60 |
| Leap year | No |
Example 2
Inputs: Date = 2000-02-29.
| Result | Value |
|---|---|
| Day of the week | Tuesday |
| Day of the year | 60 |
| Leap year | Yes |
Example 3
Inputs: Date = 1969-07-20.
| Result | Value |
|---|---|
| Day of the week | Sunday |
| Day of the year | 201 |
| Leap year | No |
The first line is the headline result (day of the week). Below it the weekday Calculator lists day of the year and leap year, which describe the same case from other angles. IEEE-754 double precision; shown to at most 6 decimal places.
Before 1582
Dates before the Gregorian reform of 1582 use the proleptic Gregorian calendar, extending today's rules backwards. Historical documents may use the Julian calendar, which gives a different weekday.
Mental method
The 'doomsday' method finds weekdays quickly by remembering anchor dates. The calculator is exact, and it is handy for birthdays, deadlines and historical dates.
Weekday from different start dates
The same calculator run from 1 January of four consecutive years.
| Date | Day of the week | Day of the year | Leap year |
|---|---|---|---|
| 2026-01-01 | Thursday | 1 | No |
| 2027-01-01 | Friday | 1 | No |
| 2028-01-01 | Saturday | 1 | Yes |
| 2029-01-01 | Monday | 1 | No |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Date: left empty shows "Enter date." beside that field and no result.
Choosing between the Weekday Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Birthday Calculator](/lifestyle/birthday/) | date of birth and reference date | Next birthday |
| [Baby Age Calculator](/lifestyle/baby-age/) | date of birth and reference date | Age |
| [Age Difference Calculator](/lifestyle/age-difference-calculator/) | first birth date and second birth date | Age difference |
| [Half Birthday Calculator](/lifestyle/half-birthday/) | date of birth | Half birthday |
| [School Age Calculator](/lifestyle/school-age/) | date of birth and school cutoff date | Age on the cutoff date |
Background: dates and times
Date and time results depend on the conventions a tool uses: whether the end date counts, whether weekends and holidays are skipped, how months of different lengths are handled and whether time zones are applied. This page states its convention, and the worked examples show it.
Dates use the Gregorian calendar and calendar days unless the page says otherwise; check deadlines against the rule in your contract or regulation.
Assumptions and limitations
- Dates before 1582 use the proleptic Gregorian calendar
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for date to confirm this.
Frequently asked questions
What weekday was 1 January 2000?
1 January 2000 was a Saturday; enter it as the date to confirm.
Does it work for the future?
Yes. The Gregorian rules extend to any future date, so you can look up weekdays years ahead.
Why does it show the leap year?
It affects the day count.
What does the Weekday Calculator calculate?
Look up the weekday (Monday to Sunday) of any past or future date. It returns Day of the week, Day of the year and Leap year.
What formula does the Weekday Calculator use?
weekday from the proleptic Gregorian calendar day count. Uses the Gregorian calendar for all dates.
What do I need to enter in the weekday Calculator?
You enter Date.
How is the result rounded or limited?
IEEE-754 double precision; shown to at most 6 decimal places. Dates before 1582 use the proleptic Gregorian calendar.
What is an example of a weekday result?
With date 2025-03-01, the day of the week is Saturday.
Related calculators
- Birthday Calculator — Next birthday, days until it, and your current age.
- Baby Age Calculator — A baby's age in weeks, months and days.
- Age Difference Calculator — Time between two birth dates.
- Half Birthday Calculator — The date six months after a birthday.
- School Age Calculator — Child's age on a school cutoff date.
- Birth Date from Age Calculator — Range of possible birth dates for someone of a given age.
Sources
- ISO 8601-1: Date and time, representations for information interchange (calendar dates, ordinal dates and week dates)
- Gregorian calendar reform, papal bull Inter gravissimas (1582): the leap-year rule used for all dates
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.