How the add time calculator carries minutes into hours

Each column adds up on its own. Every 60 seconds become 1 minute, and every 60 minutes become 1 hour in the column to the left.

Times added	Before carrying	After carrying	Decimal hours
1:45 + 2:30	3 h 75 m	4:15	4.25
0:50:30 + 0:20:45	0 h 70 m 75 s	1:11:15	1.19
7:40 + 8:15 + 6:55	21 h 110 m	22:50	22.83
2:30 + 2:30 + 2:30 + 2:30	8 h 120 m	10:00	10.00

The second row carries twice: 75 seconds turn into 1 minute 15 seconds, which makes 71 minutes, and 71 minutes turn into 1 hour 11 minutes. A row may also hold more than 59 minutes, so 0 hours 90 minutes counts as 1:30. The guide to adding hours and minutes works through more cases by hand.

Time subtraction: borrowing 60 minutes

Subtraction runs the other way. When the minutes to take away are larger than the minutes you have, one of the hours is broken into 60 minutes first.

Calculation	After borrowing	Result
8:00 − 0:45	7 h 60 m − 0 h 45 m	7:15
5:10 − 2:45	4 h 70 m − 2 h 45 m	2:25
1:00 − 2:30	2 h 30 m − 1 h 0 m, made negative	−1:30

A mixed list such as 8:00 + 1:15 − 0:45 adds and subtracts in one pass, giving 8:30. If the subtractions outweigh the additions, the total is negative, like the −1:30 in the last row. To take hours off the current time of day instead, the hours ago calculator gives the earlier clock time and date.

Totals over 24 hours and decimal hours

A sum of durations never rolls over at midnight: 19:30 + 9:00 is 28:30, or 1 day 4 hours 30 minutes. That is the right form for a weekly timesheet, where 38:45 means 38 hours 45 minutes worked.

Spreadsheets trip over this. In Excel, adding 19:30 and 9:00 with =SUM shows 4:30 in the default h:mm format, because whole days are hidden; the custom format [h]:mm shows 28:30.

For pay, the total is also given in decimal hours: 4:15 is 4.25 hours, so at $20 an hour it earns $85. The minutes to decimal hours chart lists all 60 minute values. For a full week of in and out punches, the weekly hours calculator adds each day and splits off overtime, and the time card math walkthrough explains the rules.

Adding hours to a clock time

The Time in X hours mode answers a different question: what the clock will read after a set amount of time. Hours past midnight move the answer to the next date, and each further 24 hours adds a day.

Start time	Change	Result
9:15 AM	+ 1 h 30 m	10:45 AM, same day
10:00 PM	+ 5 h	3:00 AM, next day
1:00 AM	− 2 h	11:00 PM, previous day
11:30 PM	+ 26 h 45 m	2:15 AM, 2 days later

Starting from the present moment, the hours from now calculator reads your clock and date for you. The span between a known start and end belongs to the time duration calculator. Lap or task times that you want to compare rather than total go into the average time calculator.

Frequently asked questions

How do I add a time written in decimal hours, such as 2.5 hours?

Convert it first by multiplying the decimal part by 60: 2.5 hours is 2 hours 30 minutes, so enter it as 2:30. Likewise, 1.2 hours is 1 hour 12 minutes, not 1:20.

Why can't I add times like ordinary decimal numbers?

Minutes roll over at 60, not at 100. 1:45 + 1:30 is 3:15, but adding the digits as decimals gives 2.75, which is neither 3:15 nor 3.25 hours.

Add Time Calculator

How each entry builds the total