Time Duration: 5 Mistakes to Avoid
Calculates hours and minutes between two times, including overnight shifts. 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.
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.
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.
1. Mixing date formats
5/10 can mean 5 October or 10 May depending on the convention.
2. Ignoring leap years
29 February changes day counts in leap years.
3. Not deciding whether to include the end date
Counting inclusively adds one day.
4. Assuming every month has 30 days
Month lengths vary from 28 to 31 days.
5. Overnight time errors
If a shift ends after midnight, add 24 hours before subtracting.
The correct method
Duration = end − start (+24 h if end is earlier).
For example, with these inputs:
- Start time: 09:00
- End time: 18:30
the calculator returns:
- Duration: 9 h 30 min
- In hours: 9.50 hours
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 Time Duration Calculator applies the formula consistently, so it is a quick way to double-check your own working.
Run your own numbers: Time Duration Calculator