The Time Calculator adds and subtracts durations — spans of hours, minutes and seconds — and normalises the answer into HH:MM:SS with total seconds and total minutes on the side. It's the tool you need when you're tracking billable time, splitting a workout across intervals, editing audio and video, cooking multi-stage recipes or planning a race pace.
How it works
Every duration is converted to a total number of seconds, the two totals are added or subtracted, and the result is broken back down into hours, minutes and seconds. This avoids the classic bug of adding 45 + 45 minutes and getting "1:30" without carrying the extra hour.
The formulas
- Total seconds = hours × 3600 + minutes × 60 + seconds.
- Sum = seconds₁ + seconds₂; Difference = seconds₁ − seconds₂.
- H = ⌊total ÷ 3600⌋, M = ⌊(total mod 3600) ÷ 60⌋, S = total mod 60.
Worked examples
Adding two workouts
Session A 1:15:40 + Session B 0:52:35 = 8,140 s = 2:08:15.
Subtracting a break
Shift length 9:00:00 − break 0:45:00 = 8:15:00 of paid work.
Large sum with carry
72:30:00 + 15:45:20 = 88:15:20 — the calculator does not cap at 24 hours.
Where it's used
- Freelancers logging billable hours across tasks.
- Runners and cyclists combining split times into a total.
- Video editors summing clip durations for a rough cut.
- Musicians and podcasters checking episode lengths.
- Manufacturing supervisors totalling machine run-times.
Tips and common mistakes
- Don't add times as decimals — 1.30 is not 1 hour 30 minutes, it's 1 hour 18 minutes.
- Carry the extra unit: 90 seconds is 1 minute 30 seconds, not 0:00:90.
- For start-and-end clock times (like a shift starting at 09:15 and ending at 17:40) use the Hours Calculator instead.