Time & Date · Durations

Time Calculator — Add and Subtract Hours, Minutes and Seconds

Add up and subtract durations written as h:mm, h:mm:ss or '2h 15m' — lap times, video clips, hours worked — multiply or divide a time (like a pace times a number of laps, or a total split into parts), or find the time from one clock time to another, including overnight. Results in h:mm:ss, decimal hours and total minutes.

Your inputs

Quick start — try a typical case

Calculate

Times

Use + and −; times as h:mm, h:mm:ss, or 2h 15m 10s.

Your result Live

Result

4:40:15

4 times added up

Decimal Hours: 4.6708333 hours
Total Minutes: 280.25
Total Seconds: 16,815

Step by step

4 rows

	Time	Running total
+	2:30:15	2:30:15
+	1:45:00	4:15:15
+	0:45:00	5:00:15
−	0:20:00	4:40:15

How this is calculated

Convert each time to seconds, add or subtract, convert back: h = ⌊s ÷ 3600⌋, m = ⌊(s mod 3600) ÷ 60⌋, s mod 60

Decimal hours: Seconds ÷ 3600 — e.g. 1:45 = 1.75 hours

Times don't add like ordinary numbers because 60 minutes make an hour: 1:45 + 0:30 is 2:15, not 1:75. Converting everything to seconds, doing the sum and converting back avoids the carrying mistakes. For decimal hours (useful for pay), divide the minutes by 60: 7 h 45 min is 7.75 hours.

Assumptions & sources

Durations, not dates; 'between' assumes at most one midnight crossing.

1ISO 8601 — Date and time format (durations) — International Organization for Standardization

Calculator ID TIME-ARITH-001 · version 1.0.0

Common questions

What's 2:30:15 + 1:45 + 45 minutes − 20 minutes?

4:40:15.

How do I convert 1:45 to decimal hours?

1 + 45/60 = 1.75 hours.

How many hours from 10:15 PM to 6:40 AM?

8 hours 25 minutes (8.42 hours).