Date & Time

Time Duration Calculator

Add or subtract time durations. Convert hours, minutes, and seconds.

Instant Results100% FreeAny DeviceNo Sign-up

Operation

Duration 1

Hours

Min

Sec

Duration 2

Hours

Min

Sec

What Is the Time Duration Calculator?

Time duration arithmetic requires base-60 (sexagesimal) arithmetic, unlike ordinary decimal arithmetic. Adding 1h 45m + 2h 30m doesn't simply give 3h 75m; the 75 minutes must normalise to 1h 15m, yielding 4h 15m total.

Supported Operations

›Add: combine two durations, carry seconds → minutes → hours
›Subtract: find how much longer D₁ is than D₂ (borrow from higher units)
›Multiply: scale a duration by a numeric factor (e.g. 3× a 45-min session)
›Difference: absolute gap between two durations regardless of order

Common Use Cases

›Project time tracking: sum daily work sessions
›Sports timing: add lap times, compute pace adjustments
›Media production: total runtime of video segments
›Travel planning: layover + flight + transit totals

Formula

Add Durations

(h₁+h₂) + (m₁+m₂) + (s₁+s₂), carry 60s→min, 60min→hr

Subtract

Borrow 60 sec/min and 60 min/hr as needed

Multiply Duration

Total seconds × factor → normalise

Difference

|D₁ − D₂| in total seconds → normalise

Total Seconds

h×3600 + m×60 + s

Normalise

÷3600 → hrs; remainder ÷60 → min; rest → sec

How to Use

1Select an operation: Add, Subtract, Multiply, or Difference.
2Enter Duration 1 as hours, minutes, and seconds (any field can be left as 0).
3For Add/Subtract/Difference, enter Duration 2 in the same format.
4For Multiply, enter the scalar factor (e.g. 3 for triple the duration).
5Click Calculate, result shows HH:MM:SS plus total seconds/minutes/hours equivalents.
6Use the preset buttons (1 Hour, 90 Min, etc.) to quickly fill Duration 1.

Example Calculation

Adding two work sessions: 2h 45m 30s + 1h 50m 45s:

D1 = 2h 45m 30s → 9,930 seconds D2 = 1h 50m 45s → 6,645 seconds Total = 9,930 + 6,645 = 16,575 seconds Normalise: 16,575 ÷ 3,600 = 4 hrs, remainder 1,575 1,575 ÷ 60 = 26 min, remainder 15 Result: 4h 26m 15s

Result

Two sessions total 4 hours 26 minutes 15 seconds. This is harder to track mentally in base-60, the calculator normalises carry-overs automatically.

Understanding Time Duration

Time Unit Quick Reference

Duration	Seconds	Minutes	Hours	Common Use
1 minute	60	1	0.0167	Short task
15 minutes	900	15	0.25	Quarter hour
30 minutes	1,800	30	0.5	Half hour
1 hour	3,600	60	1	Work block
90 minutes	5,400	90	1.5	Sports half, lecture
3 hours 45 min	13,500	225	3.75	Long meeting
8 hours	28,800	480	8	Workday
24 hours	86,400	1,440	24	Full day

Frequently Asked Questions

How does base-60 time arithmetic work?

Time uses a sexagesimal (base-60) system inherited from ancient Babylonian mathematics:

›60 seconds make 1 minute; 60 minutes make 1 hour
›Carry rules: if seconds ≥ 60, subtract 60 and carry 1 to minutes
›Borrow rules: if subtracting and seconds are negative, add 60 and borrow 1 from minutes
›Unlike decimal math, adding 45 + 45 minutes gives 1h 30m, not 90 minutes

What does the Multiply operation do?

›Example: one lap = 3m 45s; multiply by 8 gives total race time
›The calculator converts 3m 45s → 225 seconds, × 8 = 1,800 seconds → 30m 00s
›Useful for recurring tasks: "15 meetings of 45m each = total meeting time"
›Factor can be a decimal (e.g. 1.5 for 150% of a duration)

What is the difference between Subtract and Difference?

›Subtract (D1 − D2): D1 must be ≥ D2; if not, the result would be negative, the calculator flags this
›Difference |D1 − D2|: always positive, regardless of which duration is larger
›Use Subtract when direction matters (e.g. "overtime worked beyond 8 hours")
›Use Difference when you just want to know how far apart two durations are

Can I enter more than 59 minutes or 59 seconds?

›Entering 90 in the minutes field is fine, it normalises to 1h 30m
›Entering 3600 in the seconds field gives exactly 1 hour
›Useful when pasting in raw values from other systems without pre-converting
›Normalisation happens before the arithmetic operation, so results are always valid HH:MM:SS

How do I calculate elapsed time between two clock times?

›Express times as durations from midnight: 9:30 AM = 9h 30m; 5:15 PM = 17h 15m
›17h 15m − 9h 30m = 7h 45m elapsed
›For overnight spans (e.g. 11 PM to 6 AM): add 24h to the later time first
›Use Difference mode if you are unsure which time is larger

What is the maximum duration supported?

›No 24-hour limit, results display as total hours:minutes:seconds (e.g. 128:30:00)
›Suitable for multi-day project totals, manufacturing run times, or media durations
›Results also shown as total seconds, total minutes (decimal), and total hours (decimal)
›JavaScript numeric precision supports exact arithmetic up to ~9,000 years of seconds

How do I convert a duration to just seconds or minutes?

›1h 30m = 5,400 seconds = 90.0 minutes = 1.5 hours
›The result panel shows all three decimal equivalents alongside HH:MM:SS
›Copy the value you need directly from the result panel
›Useful for feeding totals into spreadsheets or timekeeping systems that use a single unit

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