How to Add Hours and Minutes (3 Simple Methods)
To add hours and minutes, add the minutes first: every 60 minutes carries over as 1 hour. Then add the hours plus anything you carried. For example, 8:15 + 7:45 gives 15 + 45 = 60 minutes = 1 hour, so 8 + 7 + 1 = 16:00 — not 15.6.
Why 8:15 + 7:45 is 16:00, not 15.6
The trap is treating a time like 8:15 as the decimal number 8.15. Minutes only run from 0 to 59, but decimals run 0 to 99, so the two don't line up. Forty-five minutes is three-quarters of an hour — 0.75, not 0.45.
Punch 8.15 + 7.45 into a normal calculator and you get 15.6, which is meaningless as a time. Do it properly and 15 minutes plus 45 minutes is a full hour, which rolls the total up to 16 hours flat. Getting this wrong on a timesheet quietly loses or adds real paid time, so it's worth doing carefully.
Method 1: The manual carry method
This is the pen-and-paper way, and it always works. Keep hours and minutes in separate columns.
- Add the minutes. Sum every minute value on its own. For 8:15 + 7:45, that's 15 + 45 = 60 minutes.
- Carry each full hour. For every 60 minutes, add 1 to the hours column and subtract 60 from the minutes. 60 minutes becomes 1 hour and 0 minutes left over.
- Add the hours. Sum the hour values, then add whatever you carried: 8 + 7 + 1 = 16.
- Write it as H:MM. Combine the hours with the leftover minutes:
16:00.
Worked example: a three-shift week fragment
Say you worked three shifts of 8:15, 7:45, and 6:30 and want the total.
- Minutes: 15 + 45 + 30 = 90 minutes. That's 1 hour and 30 minutes, so carry 1 and keep 30.
- Hours: 8 + 7 + 6 = 21, plus the 1 you carried = 22.
- Total: 22:30 (22 hours 30 minutes).
You can sanity-check that with decimals: 8.25 + 7.75 + 6.5 = 22.5 hours, and 22.5 hours is 22 hours 30 minutes. The two methods agree.
Method 2: The decimal method
Sometimes it's easier to convert each time to decimal hours, add normally, then convert back. Divide the minutes by 60 to get the decimal part. These four values cover most timesheet entries:
| Minutes | Decimal | Example |
|---|---|---|
| 15 | 0.25 | 8:15 = 8.25 |
| 30 | 0.50 | 1:30 = 1.5 |
| 45 | 0.75 | 7:45 = 7.75 |
| 60 | 1.00 | rolls to the next hour |
So 8:15 + 7:45 becomes 8.25 + 7.75 = 16.00 hours, which is 16:00. To turn a decimal back into minutes, multiply the fractional part by 60: 0.5 × 60 = 30, so 16.5 hours is 16:30. Decimal hours are also exactly what most payroll systems want, so this method doubles as prep for pay.
Method 3: Let the Hours app do it
The fastest, least error-prone method is to let an app handle the carrying. Hours: Time Card Calculator lets you type times in plain H:MM and add, subtract, multiply, and divide them without ever converting anything by hand.
- Add and subtract times in H:MM — the carry happens automatically.
- Overnight and negative totals are handled (no 24-hour cap).
- One tap flips the total between H:MM and decimal hours.
- Set an hourly rate to turn hours into pay, and export a timesheet to CSV or PDF.
It's free, works offline, has no ads, and needs no account or sign-in.
Add time without the mental math
Hours does the carrying for you, flips to decimal in one tap, and turns totals into pay. Free, offline, no sign-in.
Frequently asked questions
What is 8:15 + 7:45?
8:15 + 7:45 = 16:00. The minutes 15 + 45 make 60, which is one full hour, so you carry 1 to the hours: 8 + 7 + 1 = 16 hours and 0 minutes.
Why can't I just add times on a normal calculator?
A normal calculator treats 8.15 + 7.45 as decimals and returns 15.6, which is wrong for time. Minutes run 0 to 59, not 0 to 99, so 45 minutes is 0.75 of an hour, not 0.45. You must either carry every 60 minutes or convert to true decimal hours first.
How do I convert minutes to decimal hours?
Divide the minutes by 60. 15 minutes = 0.25, 30 minutes = 0.5, and 45 minutes = 0.75. So 1:30 is 1.5 hours and 8:15 is 8.25 hours.