Time Calculator
Add or subtract hours, minutes and seconds, find the duration between two clock times, or convert between seconds, minutes, hours and days — all in your browser.
Add or subtract any number of durations. Use the +/- on each row to choose whether it counts toward or against the total.
Total (HH:MM:SS)
00:00:00
In hours
0
In minutes
0
In seconds
0
Frequently Asked Questions
Can it add multiple durations together?
Yes. In the "Add / Subtract" mode you can add as many duration rows as you like, each with hours, minutes and seconds. Use the +/- toggle on every row to choose whether it adds to or subtracts from the running total, which can go negative.
Can it find the time between two clock times?
Yes. The "Between two times" mode takes a start time and an end time and returns the duration. Dates are optional — leave them blank to treat both times as the same day, or add dates to span across days.
Does it convert between time units?
Yes. The "Convert" mode takes a single value and unit and instantly converts it across seconds, minutes, hours and days, and also shows it formatted as HH:MM:SS.
Understanding the Time Calculator
The Time Calculator is a fast, fully client-side tool for everyday time math. It has three modes. "Add / Subtract" lets you stack as many duration rows as you want — each with hours, minutes and seconds and a +/- toggle — then sums them into a clean, normalized total (carrying seconds into minutes and minutes into hours), shown as HH:MM:SS plus equivalents in hours, minutes and seconds. "Between two times" finds the duration between a start and end clock time, with optional dates for spans that cross days. "Convert" turns any value into seconds, minutes, hours and days at once. Everything runs in your browser, so nothing is uploaded.
How it works
Every input is reduced to a single signed count of seconds, which keeps the arithmetic simple and exact. In Add / Subtract mode, each row becomes hours×3600 + minutes×60 + seconds, then is added or subtracted based on its sign; the running total may go negative. To display a result, the tool takes the absolute value, divides by 3600 for whole hours, takes the remainder for minutes, then seconds — classic modular carrying — and prefixes a minus sign when negative. Between-times mode converts each clock time (and optional date) to seconds and subtracts; with no dates, negative gaps wrap to the next day. Convert mode multiplies by the unit's seconds, then divides out each target unit.
Worked example
Suppose you logged three work sessions: 1 h 45 m, 2 h 30 m, and 50 m, but took a 25 m break to subtract. Add three +rows and one −row. The tool computes 6300 + 9000 + 3000 − 1500 = 16800 seconds, normalizes it, and shows 04:40:00 — that is 4.6667 hours, 280 minutes, or 16,800 seconds — ready to copy or export as CSV.
Tips & common mistakes
- Leave a field blank to treat it as zero — you do not need to type 0 in every box.
- Use the per-row +/- toggle to mix additions and subtractions; the total can legitimately go negative.
- In Between-two-times mode, leave the dates blank for same-day gaps; a negative result simply wraps into the next day.
- Add dates on both sides when a shift or event crosses midnight so the duration spans more than 24 hours.
- Convert mode is handy for sanity checks — e.g. confirm 90 minutes is 1.5 hours or 5,400 seconds.
- Use the Copy, CSV and Print buttons to save a result into a timesheet, invoice or note.