Working Days: 5 Mistakes to Avoid
Counts weekdays between two dates, inclusive. Subtract any public holidays that fall on a weekday. The maths is not complicated, but a handful of errors come up again and again in this and related date & time calculations. Here is what to watch for.
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.
When sharing dates internationally, write the month as a word to avoid confusion between day-month and month-day formats.
1. Mixing date formats
5/10 can mean 5 October or 10 May depending on the convention.
2. Assuming every month has 30 days
Month lengths vary from 28 to 31 days.
3. Ignoring leap years
29 February changes day counts in leap years.
4. Not deciding whether to include the end date
Counting inclusively adds one day.
5. Overnight time errors
If a shift ends after midnight, add 24 hours before subtracting.
The correct method
Count Monday to Friday dates in the range.
For example, with these inputs:
- Start date: 1 Oct 2026
- End date: 31 Oct 2026
the calculator returns:
- Weekdays (Mon–Fri): 22 days
- Calendar days: 31 days
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.
The Working Days Calculator applies the formula consistently, so it is a quick way to double-check your own working.
Run your own numbers: Working Days Calculator