How to Add and Subtract Time (Hours and Minutes)

Add 2:45 and 1:30 the way you'd add two decimals and you get 3.75, which isn't a real time at all. Hours and minutes don't carry at 10 or 100 — they carry at 60, the same way a stopwatch's seconds hand rolls the minute hand forward the instant it passes 59. Once that single rule is second nature, adding and subtracting time — whether you're combining two lengths of time or shifting a clock time forward or back — is just ordinary arithmetic with one extra step.

This guide covers that method properly: adding durations, subtracting them with borrowing, and applying both operations to a clock time rather than just another duration. If you'd rather not do it by hand, the time calculator handles all four cases instantly. If you want to actually understand the mechanics — for a spreadsheet formula, a timesheet, or just your own head — read on.

A minutes column can only hold values from 0 to 59. The moment a sum would push it to 60, that 60 rolls over into a whole extra hour, and the minutes column resets by 60. Subtraction runs the same rule backward: if you don't have enough minutes to subtract from, you borrow a whole hour from the hours column and convert it into 60 extra minutes. Get the direction right — carry going up, borrow going down — and the arithmetic underneath is nothing more than adding or subtracting two numbers.

Add the minutes together, add the hours together, then check the minutes total: if it has reached 60 or more, subtract 60 from it and carry 1 into the hours.

Subtraction works the same way in reverse. If the minutes you're subtracting are larger than the minutes you're subtracting from, borrow 1 hour from the hours column, turn it into 60 minutes, and add it to the top before subtracting.

Adding a length of time to a clock time — "what time is 2 hours 45 minutes from 6:30 PM?" — uses the same carry rule, but it's easiest to do without ever separating AM from PM: convert the clock time to minutes past midnight, add the duration in minutes, then convert the total back to a clock time.

Subtracting works the same way, converted through minutes: if the result goes below zero, add 1440 — the answer falls on the previous day.

Add or subtract two durations below — enter each as hours and minutes, like 2:45.

• Treating 75 minutes like ".75 of an hour" instead of carrying it correctly — 60 minutes make an hour, not 100.
• Subtracting minutes without borrowing when the top number is smaller, and ending up with an incorrect negative minutes figure instead of borrowing an hour first.
• Mixing decimal hours and hours-and-minutes in the same sum — adding "1.5 hours" directly to "45 minutes" gives 46.5 instead of the correct 2 hours 15 minutes. Convert one format into the other first; see How to Convert Minutes to Decimal Hours for Payroll.
• Forgetting that adding or subtracting across midnight moves the result to the next or previous day, rather than just wrapping the clock face in place.
• Reaching for this method when the real question is the gap between two clock times you already know, rather than combining a time with a duration — see the comparison below.

Adding and subtracting time combines a known duration with a clock time or with another duration — you already know the length of time involved, and you're calculating a new total or a new clock time. A few related questions ask something different:

• "Duration between two times" works backward: you know a start and an end clock time and want to find the unknown span between them, rather than add a known one. See How to Calculate the Duration Between Two Times.
• "Hours between two times" is the same backward question, but wanting a fast, rounded estimate rather than a minute-exact figure. See How Many Hours Between Two Times? A Simple Method.
• Elapsed time measures from a fixed starting moment up to right now, rather than combining two fixed values. See How to Calculate Elapsed Time.