Day of the Week Calculator
Enter any date to see which day of the week it is, plus its week number, day of the year and quarter.
What this tool does
A day of the week calculator tells you which weekday a date falls on. Enter a date and it returns the weekday, the ISO week number, the day of the year, the quarter, and whether the year is a leap year and how many days remain in it.
Works out the weekday for any date from the Gregorian calendar.
Also gives the ISO 8601 week number, the day of the year, the quarter, leap-year status and days remaining.
How to use it
- Enter the date.
- Read the weekday in large type.
- Check the ISO week number and the day of the year.
- Use the quarter and days-left figures for planning.
- Press Copy results to paste them.
Why use a day of the week calculator
Gives the weekday together with the ISO week number, day of the year, quarter and leap-year status for the same date. Knowing the weekday of a past or future date helps with birthdays, anniversaries, deadlines and historical dates. Week numbers matter for work schedules and invoices, and the ISO rule has surprises at the year boundary.
Why we built it
We built the day of the week calculator to show the weekday together with the ISO week number, day of the year, quarter and leap-year status for the same date, because those are usually needed together. The week number calculator goes further on ISO weeks, and the leap year calculator checks any year.
Related tools worth a look: the Year Planner.
Who this tool is for
- Genealogists finding the weekday of a historical date
- Event planners checking what day a date falls on
- Students and quiz fans
When to use it
- Finding the weekday you were born or married.
- Checking what day a deadline or event falls on.
- Working out the ISO week number for a schedule.
- Finding the day of the year or the quarter.
How it is calculated
The weekday comes from the calendar date. ISO weeks start on Monday, and week 1 is the week containing the first Thursday of the year, so a date in early January can belong to the previous year’s last week.
Worked example: 1 January 2000 was a Saturday. 3 January 2021 was a Sunday and belongs to ISO week 53 of 2020.
Some countries number weeks differently, for example weeks starting on Sunday. The ISO week used here is standard in Europe and in much business use.
What you enter, and what you get back
| Item | Details |
|---|---|
| Date | Any valid date. |
| Result | Weekday, day of the year, ISO week, quarter, leap year and days remaining. |
Issues you may run into
| What you see | Why it happens | What to do |
|---|---|---|
| Week number differs from my calendar | Your calendar uses a different week system. | ISO weeks start on Monday and week 1 has the first Thursday. |
| Date refused | The date does not exist, like 30 February. | Check the day and month. |
| Wrong weekday for an old date | Before the Gregorian switch the calendar differed. | Dates before 1582 may not match historical records. |
A worked example
These are the values the calculator opens with, so you can see exactly what it does with them. Change any value on the page and the result updates; the figures below come from the same calculation.
| Input | Value |
|---|---|
| Date | 2026-03-15 |
With those inputs, the calculator returns:
- 2026-03-15: Sunday
- Day of the year: 74 of 365
- ISO week number: Week 11 of 2026
- Quarter: Q1
- Leap year: No
- Days left in the year: 291
Assumptions and limitations
- Proleptic Gregorian calendar - older historical dates may differ from records.
- ISO week numbering only.
- No time zone or time of day.
- Uses your device’s date for “today”.
Frequently asked questions
What day of the week was I born?
Enter your date of birth and the weekday is shown in large type, with the week number and day of the year.
How is the ISO week number worked out?
Weeks run Monday to Sunday and week 1 is the week with the first Thursday of the year. Early January dates can belong to week 52 or 53 of the previous year.
Is the year a leap year?
The result states it. A year is a leap year if divisible by 4, except century years not divisible by 400.
What is the day of the year?
The count of the date from 1 January, so 1 January is day 1 and 31 December is day 365 or 366.
Does it work for dates far in the past or future?
Yes, using the Gregorian calendar throughout. Very old dates may not match the calendars used at the time.