Day of the Week Formula Explained, With Examples
Every day of the week result comes from one formula. Once you understand what goes into it, you can sanity-check any figure you are given, whether by an employer, a bank, a teacher or another website.
The formula
Based on the Gregorian calendar.
What each input means
- Date: the value you enter in the calculator.
Example
For example, with these inputs:
- Date: 9 Aug 1965
the calculator returns:
- Day: Monday
Why it matters
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.
When sharing dates internationally, write the month as a word to avoid confusion between day-month and month-day formats.
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.
Many Singapore rules are expressed in days: notice periods, leave entitlements, stamp duty deadlines and probation periods. Whether the count includes the start or end date, and whether weekends count, changes the answer.
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.
Use the Day of the Week Calculator to plug in your own numbers.
Run your own numbers: Day of the Week Calculator