Add or Subtract Time Calculator
Add or subtract hours and minutes from a date and time.
This tool runs entirely in your browser. Your files are never uploaded to a server.
What this tool does
Adds or subtracts a chosen number of hours or minutes from a date and time and shows the resulting date and time.
How to use it
Pick a starting date and time, choose Add or Subtract, an amount, and a unit (Minutes or Hours). Reset returns to the default example: adding 7 hours to 2026-01-01 at 12:00.
Worked example
Adding 7 hours to 2026-01-01 12:00 gives 2026-01-01 19:00 the same day. Switching the unit to Minutes and adding 90 minutes to that same starting point gives 2026-01-01 13:30 instead.
Method and local time zone
Unlike the Add or Subtract Days Calculator, which fixes its arithmetic to UTC, this tool parses the date and time you enter as your browser's local time, because a datetime-local input has no time-zone suffix. The chosen amount is converted to minutes (multiplying by 60 for hours) and added to or subtracted from that local time, then displayed in your browser's local time zone and locale.
Units and fractional amounts
Amounts can include decimals — 1.5 hours becomes 90 minutes — but JavaScript's Date.setMinutes only accepts whole minutes, so any fractional minute left over after the conversion (for example from 0.017 hours) is truncated rather than rounded.
Limitations
Because the calculation uses your browser's local time zone rather than a fixed one, the same input can produce a different result on a device set to a different zone, and results can shift by an hour around a daylight-saving transition. It also only adds hours and minutes, not days — for whole-day arithmetic, use the Add or Subtract Days Calculator instead.
Privacy and processing
The calculation runs entirely in your browser using JavaScript's Date object. The date and time you enter are never uploaded or stored.
Frequently Asked Questions
- Does this use my local time zone or UTC?
- Your local time zone — a datetime-local input has no time-zone suffix, so the entered date and time are parsed and displayed using your browser's local clock, unlike the UTC-based Add or Subtract Days Calculator.
- What happens with fractional hour or minute amounts?
- Decimals are allowed and converted to minutes (1.5 hours becomes 90 minutes), but JavaScript's Date.setMinutes only accepts whole minutes, so any leftover fraction of a minute is truncated rather than rounded.
- Can I add or subtract whole days instead of hours and minutes?
- This tool only handles hours and minutes. For whole-day arithmetic on a calendar date, use the Add or Subtract Days Calculator instead.
- Does the result account for daylight-saving transitions?
- It follows your device's local clock, so if the calculated time crosses a daylight-saving change, the displayed result reflects whatever your browser shows for that local time — verify manually for transition-sensitive scheduling.