Day of the Week Calculator

1. Pick any date using the date picker.
2. Read the day of the week it falls on.
3. See the day number within that year.
4. Check whether it is a weekday or weekend.

Here is what each result means:

The day of the week is where a date falls in the seven-day cycle from Sunday to Saturday. Because the cycle repeats every seven days, any date in history or the future lands on exactly one of these days, and it can be worked out precisely from the calendar. People often want to know the weekday of a birthday, a historical event or a future deadline.

Working it out by hand is fiddly because month lengths vary and leap years add a day, which shifts every later date. This calculator does it instantly using the Gregorian calendar, the civil calendar in use across the world today. It simply counts the days from a known reference point and takes the remainder after dividing by seven.

Alongside the weekday, knowing the day number within the year is useful for planning and scheduling. The first of January is day 1, and the last day is 365, or 366 in a leap year. Together, the weekday and the day number pin down exactly where a date sits in both the weekly and yearly cycles.

It counts days from a fixed reference and uses the remainder after dividing by seven.

1. The date you pick is read on the Gregorian calendar.
2. The number of days from a known reference date is counted, allowing for leap years.
3. Dividing that count by seven gives the weekday, and the remainder points to the exact day.

For related date tools, see the date calculator and the age calculator.

Take 1 January 2000.

Result: that date was a Saturday, and being the first of January it was day 1 of the year 2000. As 2000 was a leap year, that year ran to 366 days. Picking 4 July 1776 instead shows it fell on a Thursday.

The week runs in a fixed cycle, though different traditions treat different days as the start.

The international standard ISO 8601 treats Monday as the first day of the week, while calendars in some countries start on Sunday. This calculator names the day itself, so the starting-day convention does not change the answer.

The weekday of a very old date depends on which calendar was in use.

This tool uses the proleptic Gregorian calendar, meaning it applies today's rules even to dates before 1582. Historical records from that era may have used the Julian calendar, so a very old weekday quoted here can differ from a contemporary source by a few days.

Leap Years

An extra day on 29 February shifts every later date forward by one weekday compared with a common year.

Month Lengths

Months of 28 to 31 days move the cycle along by different amounts, which is why the pattern is not obvious by eye.

The Century Rule

Years divisible by 100 but not 400 skip their leap day, which nudges the weekday of later dates.

Birthdays and Events

Find out which day you were born, or the weekday of a memorable date.

Planning Ahead

Check whether a future deadline or event lands on a weekend.

History and Trivia

Settle what day a historical event took place.

1. Forgetting Leap Years

Counting weekdays by hand often misses the extra day in a leap year, giving the wrong result.

2. Mixing Calendars

Very old dates may be recorded on the Julian calendar, so compare like with like.

3. Off-by-one in the Day Number

The first of January is day 1, not day 0, so the day-of-year count starts at one.

4. Assuming the Week Starts on Sunday

The ISO standard starts the week on Monday, though the named day is the same either way.

5. Time-zone Confusion

A date is a whole calendar day here, so time of day and time zone do not change the weekday.

The weekday is exact on the Gregorian calendar for any date you enter.

Pick your date of birth in the calculator and it shows the weekday instantly. For example, someone born on 1 January 2000 was born on a Saturday.

Count the days from a date whose weekday you know, allowing for leap years, then divide by seven. The remainder tells you the weekday.

It was a Saturday. Because 2000 was a leap year, that year had 366 days.

Yes. It allows for the extra day on 29 February, which shifts the weekday of every later date by one compared with a common year.

It is the date's position counting from 1 January as day 1. The last day of the year is day 365, or day 366 in a leap year.

It depends on the convention. The ISO standard starts the week on Monday, while some countries start on Sunday. The named weekday is the same either way.

Yes, but it uses today's Gregorian calendar throughout. Dates before 1582 may have been recorded on the older Julian calendar and can differ by a few days.

No. A date is treated as a whole calendar day, so the time and time zone do not change which weekday it falls on.

No. The calculation runs in your browser and nothing you enter is stored or sent anywhere, unless you choose Save, which keeps the result only on this device.

• Day of the week (Wikipedia).
• Gregorian calendar (Wikipedia).
• ISO 8601 (Wikipedia).