Time Calculator

How to use the Time Calculator

1. Pick a mode: Add, Subtract, Difference or Duration.
2. For Add or Subtract, type two durations as hours, minutes and seconds — any box may be left blank (it counts as zero).
3. For Difference, enter a start time and an end time in 24-hour format, and tick “crosses midnight” if the end is on the next day.
4. For Duration, enter one length of time to convert it to total seconds, minutes and hours.
5. Press Calculate (or the Enter key), then Copy result or Reset.

What the Time Calculator does

The Time Calculator works with lengths of time and clock times down to the second. It can add two durations together, subtract one from another, measure the gap between two times of day, and convert a single duration into total seconds, minutes and hours. Every calculation runs on whole seconds rather than clock parsing, so results are exact and never affected by time zones or daylight-saving changes.

Adding time

Add mode sums two durations and tidies the result so it never spills over. Enter each duration as hours, minutes and seconds — and you can overload a single box if it is easier. For example, 1 hour plus 90 minutes is shown as 2 hours 30 minutes, and 45 minutes plus 90 seconds becomes 46 minutes 30 seconds. This is handy for totalling task times, lap times or work sessions.

Subtracting time

Subtract mode takes the second duration away from the first and borrows correctly across minutes and hours. So 5:30:00 minus 2:15:00 is 3:15:00, and 1:00:00 minus 0:30:30 is 0:29:30. If the second duration is longer than the first, the result is shown as a clearly labelled negative time (for example −0:29:30) rather than an error, so the size of the gap is still obvious.

Time difference (including overnight)

Difference mode measures the elapsed time between a start time and an end time written in 24-hour format. From 09:00 to 17:00 is 8 hours; from 09:30 to 12:45 is 3 hours 15 minutes. When a period runs past midnight, tick “crosses midnight (overnight)” and the calculator adds a day — so 23:00 to 01:00 is 2 hours, and 23:59 to 00:01 is 2 minutes. If you leave that box unticked and the end time is earlier than the start time, the tool asks you to confirm rather than quietly returning the wrong answer.

Duration and conversions

Duration mode converts one length of time into every common unit at once. Enter the hours, minutes and seconds and you get the normalised duration plus the totals: 1 hour 30 minutes is 5,400 seconds, 90 minutes, or 1.5 hours. Decimal hours use sensible precision, so you see 1.5 rather than 1.4999999. This is useful for timesheets, billing and any time you need the same length expressed in different units.

Examples

• Add 1h + 90m = 2h 30m
• Add (seconds) 45m + 90s = 46m 30s
• Subtract 5:30:00 − 2:15:00 = 3:15:00
• Difference 09:00 → 17:00 = 8 hours
• Overnight 23:00 → 01:00 = 2 hours
• Duration 1h 30m = 5,400 seconds = 90 minutes = 1.5 hours

Benefits and use cases

• Timesheets & billing — add up worked hours and convert them to decimal hours.
• Shifts & rotas — measure a shift that runs past midnight without guesswork.
• Cooking, sport & study — total lap times, intervals or sessions.
• Planning — work out how long is left, or how long something took.

Is it private?

Yes. The Time Calculator runs entirely in your web browser using JavaScript. The times you enter are never sent to a server, never stored, and never shared. There is no sign-up and no tracking.