Time Calculator (Add / Subtract Hours & Minutes)

What time will it be in 3 hours 45 minutes? What time was it 90 minutes ago? Add or subtract any duration from a clock time — day rollovers across midnight handled automatically.

How to use this calculator

Enter the start time in 24-hour HH:MM.
Choose add or subtract and enter the hours and minutes.
Press the button — crossing midnight is flagged as next/previous day.

Formula used

Result = (Start in minutes ± duration) mod 1440

Time-of-day arithmetic wraps at 1440 minutes (24 hours). The minutes column carries into hours at 60 — the base-60 carry is where manual time addition usually slips (e.g. 14:30 + 0:45 is 15:15, not 14:75).

Example calculation

Worked example

14:30 + 3h 45m: minutes 30 + 45 = 75 → carry: 1h 15m → 18:15 (6:15 PM).

23:20 + 2h = 01:20 next day — the wrap across midnight the calculator flags automatically.

Base-60 time arithmetic

Time addition trips people because it's base 60, not base 10: 45 + 30 minutes is 1 hour 15, and hour 23 + 2 wraps to 1. Every scheduling task — cooking stages, flight arrivals, medicine intervals, shift ends — is this same modular arithmetic.

The reliable manual method: convert everything to minutes, add or subtract, then divide by 60 for the hours and take the remainder as minutes, wrapping at 24 hours. This calculator shows exactly that decomposition.

Why use this calculator?

Compute arrival times, cooking schedules and medication intervals instantly.
Cross midnight safely — flagged clearly as next/previous day.
Get the answer in both 24-hour and AM/PM formats.

Frequently asked questions

What time will it be in 45 minutes?

Enter the current time, choose Add, and put 0 hours 45 minutes. If the minutes exceed 59, an hour carries over: 14:30 + 45 min = 15:15.

How do I add times longer than a day?

Enter the hours directly — 30 hours works. The result shows how many days it rolled over. For adding days/weeks/months to a calendar date, use our date add & subtract calculator instead.

Why can't I enter negative hours?

Use the Subtract direction instead — it keeps the input unambiguous and the shown working clean.