How to Calculate Day of the Week: A Step-by-Step Guide
Tells you which weekday any date falls on.
Dates and durations matter for notice periods, leave planning, project deadlines and contracts. Counting days on a calendar is slow and easy to get wrong, especially across months of different lengths.
What you need
- Date
Step by step
- Enter the date.
- The results update as you type, or press Calculate.
- Read the day first, then the supporting figures below it.
The formula
Based on the Gregorian calendar.
Worked example
For example, with these inputs:
- Date: 9 Aug 1965
the calculator returns:
- Day: Monday
Practical tips
- Leap years add a 29 February every four years, except most century years.
- Decide upfront whether the end date should be counted, because it changes the answer by one day.
- Write dates in an unambiguous format such as 5 Oct 2026 when sharing deadlines.
- Public holidays are not weekends; subtract them separately when counting working days.
Background
Singapore has 11 gazetted public holidays a year, and when one falls on a Sunday the following Monday is a holiday. Working-day calculations therefore need holidays removed separately from weekends.
Time durations are easier to handle in minutes. Convert each time to minutes after midnight, subtract, then convert back to hours and minutes, adding 24 hours for shifts that run past midnight.
When sharing dates internationally, write the month as a word to avoid confusion between day-month and month-day formats.
Related calculations
- Age Calculator: Calculates exact age in years, months and days.
- Days Between Dates Calculator: Counts days between two dates.
- Add Days to a Date Calculator: Finds the date a number of days after another date.
- Subtract Days from a Date Calculator: Finds the date a number of days before another date.
Want to skip the arithmetic? The free Day of the Week Calculator does all of this instantly and updates as you type.
Run your own numbers: Day of the Week Calculator