Time Calculator

How to use it

1. Choose a mode. Add / subtract durations totals a list of times. Clock time ± duration moves a time of day forward or back.
2. In the first mode, type days, hours, minutes or seconds on each row. Tap the + button on a row to turn it into a subtraction.
3. Add as many rows as you need. The total updates as you type and is tidied up automatically, so 1 hr 75 min shows as 2 hrs 15 min.
4. In the second mode, enter a start time (and a date if the result may land on another day), choose Add or Subtract, and enter the amount of time.

Worked examples

Totalling video clips

An editor has three clips: 12 min 40 s, 8 min 55 s and 21 min 30 s, and needs to cut 4 min 15 s overall.

1. Seconds: 40 + 55 + 30 − 15 = 110 seconds = 1 minute 50 seconds.
2. Minutes: 12 + 8 + 21 − 4 = 37 minutes, plus the 1 carried = 38 minutes.
3. Total: 38 min 50 s, or 0.65 decimal hours.

When will it finish?

A slow-cooker recipe goes in at 9:15 PM and needs 10 hours 30 minutes. 9:15 PM + 2 h 45 min reaches midnight, and the remaining 7 h 45 min lands at 7:45 AM the next day, shown with a “+1 day” tag.

How it’s calculated

Everything is converted to seconds, added up, then split back out:

total seconds = Σ (± (days × 86,400 + hours × 3,600 + minutes × 60 + seconds))

• The total is then broken into days, hours, minutes and seconds, so overflow carries over: 90 minutes becomes 1 hour 30 minutes.
• Decimal hours = total seconds ÷ 3,600, rounded to two places. Decimals are allowed in the inputs, so 1.5 hours works.
• For clock times, the duration is added to the start time and the result is wrapped around midnight. The number of whole days crossed is shown as “+1 day”, “−1 day” and so on, and the date moves with it if you entered one.
• Clock times are treated as wall-clock times, so daylight-saving changes are not applied in this mode. Use the time duration calculator with dates for that.