Time Calculator
Duration A
Duration B
Duration to apply
This adds/subtracts a fixed real-world duration — for adding calendar months or years to a date (which needs to account for different month lengths), use the Date Calculator instead.
Free time calculator with two modes: combine two durations (days, hours, minutes, seconds) with add/subtract, or apply a duration to a specific date and time.
How it works
- Choose "Combine two durations" or "Apply to a date & time"
- Enter the duration(s) in days, hours, minutes, and seconds, and pick add or subtract
- See the combined duration, or the resulting date and time
Frequently asked questions
How is this different from the Date Calculator?
This calculator works with fixed real-world durations (exactly 36 hours, for example). The Date Calculator's add/subtract mode works with calendar units (months, years) that vary in length — use that one when "1 month" should mean "the same date next month," not a fixed number of hours.
Can I subtract a bigger duration than I started with?
Yes — the result shows as negative (e.g. "-1d 2h") rather than an error, in "Combine two durations" mode.
Related tools
From the blog
Update history
- 2026-09-01 Launched: time calculator with a duration-combining mode and a date & time application mode, both down to the second. Entirely client-side.