Adding hours and minutes without the headache
Time does not add up like ordinary numbers. Fifty minutes plus twenty minutes is not seventy of anything you can use; it is 1 hour and 10 minutes. Sixty minutes to the hour and 24 hours to the day are exactly where quick mental maths goes wrong.
This time calculator handles the three jobs people need most. It adds or subtracts two lengths of time, it multiplies or divides a time (say, one class length by the number of classes in a term), and it moves a clock time forward or back, so you can see what time it will be 7 hours and 45 minutes after 9:30.
Using the calculator
- Pick what you want to work out: Add or subtract times, Multiply or divide a time, or Add time to a clock time.
- Fill in the boxes for days, hours, minutes and seconds. Leave a box at 0 if you do not need it.
- Choose Add or Subtract, or Multiply by or Divide by.
- The answer updates as you type. Under it you get the same time in decimal hours, in minutes and in seconds, plus each step the calculator took.
- Press Copy result to paste the answer somewhere else, or Copy link to share the exact numbers you used.
How the maths works
Every time is first turned into seconds, because seconds are a single unit you can add, subtract, multiply and divide like any other number. The answer is then split back into days, hours, minutes and seconds.
seconds = days × 86,400 + hours × 3,600 + minutes × 60 + seconds
decimal hours = total seconds ÷ 3,600
new clock time = start time + time added, rolling over every 24 hoursFor a clock time, the calculator counts minutes from midnight. A day has 1,440 minutes, so once the total passes that, it rolls over to the next day and tells you so. Subtracting works the same way in reverse, which is useful for working back from an arrival time to a departure time.
Worked example: two days of tracked work
You spent 3 hours 20 minutes on a project on Monday and 2 hours 55 minutes on Tuesday. What is the total?
- Monday: 3 × 3,600 + 20 × 60 = 12,000 seconds
- Tuesday: 2 × 3,600 + 55 × 60 = 10,500 seconds
- Together: 12,000 + 10,500 = 22,500 seconds
- Back to hours: 22,500 ÷ 3,600 = 6.25 hours
So the total is 6 hours 15 minutes, which is also 375 minutes. On a timesheet or an invoice you would usually write it as 6.25 hours. If you bill by the hour, the free invoice generator takes that figure straight into a line item.
Decimal hours or hours and minutes?
The answer shows both, and it matters which one you use. 6 hours 15 minutes is 6.25 hours, not 6.15. Payroll, spreadsheets and invoices nearly always want decimal hours. Rotas, travel plans and recipes read more naturally in hours and minutes.
| Minutes | Decimal hours |
|---|---|
| 5 | 0.08 |
| 10 | 0.17 |
| 15 | 0.25 |
| 20 | 0.33 |
| 30 | 0.5 |
| 40 | 0.67 |
| 45 | 0.75 |
| 50 | 0.83 |
Common slip-ups
- Writing 1.30 for an hour and a half. As decimal hours, 1.30 is 1 hour 18 minutes. An hour and a half is 1.5 hours, or 1:30 on a clock.
- Carrying at 100 instead of 60. Adding 1:45 and 0:30 as if they were normal numbers gives 1:75, which is really 2:15.
- Forgetting the change of day. 22:00 plus 5 hours is 03:00 the next morning. The clock option shows which day you land on, so night shifts and late trains do not catch you out.
- Rounding too early. If you round each entry to the nearest quarter hour before adding, small errors pile up over a week. Add the exact times first and round the total only if you have to.
Frequently asked questions
How do I add hours and minutes together?
Add the hours and the minutes separately. If the minutes come to 60 or more, take 60 away and add 1 to the hours. For 2:45 plus 1:30 you get 3 hours and 75 minutes, which becomes 4 hours 15 minutes. The calculator does this carrying for you, including seconds and whole days, and shows each step.
How do I convert minutes to hours?
Divide the minutes by 60. So 90 minutes is 1.5 hours and 135 minutes is 2.25 hours. To write it as hours and minutes instead, the whole number is the hours and what is left over is the minutes: 135 minutes is 2 hours 15 minutes. Every answer here is shown both ways.
Can I subtract one time from another?
Yes. Choose Add or subtract times, enter the larger time first and pick Subtract. If the second time is bigger, the answer starts with minus, which tells you how far short you are. To find the time between two clock readings, like 08:45 and 17:10, the time duration calculator is quicker.
What time will it be in a set number of hours?
Choose Add time to a clock time, enter the starting time, then the hours and minutes to add. The answer shows the new time in both 24 hour and 12 hour form and says whether it falls on the same day, the next day or several days later. Pick Subtract to count backwards instead.
How do I total the hours for a job I charge by the hour?
Add each session here, or use Multiply if every session is the same length. Then bill the decimal hours: 6 hours 15 minutes is 6.25 hours, so at 40 an hour the charge is 250. For a whole week of start and finish times with breaks, the time card calculator is easier.
Related calculators
Turn your hours into an invoice
Tracked the time? The free invoice generator turns your hours and rate into a PDF invoice in a couple of minutes. CloveDesk then keeps quotes, invoices, e-signatures and files for each client in one place.
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