When time addition gives you 6:15 instead of 5:75
Time runs on base-60. Add the minutes, carry every 60 as one hour, then add the hours.
Step-by-step: 3 hours 50 minutes plus 2 hours 25 minutes.
- Add the minutes: 50 + 25 = 75 minutes.
- 75 minutes exceeds 60. Carry 1 hour, leaving 15 minutes.
- Add the hours: 3 + 2 + 1 (carried) = 6 hours.
- Result: 6 hours 15 minutes.
When to be careful: If the times cross a clock change (midnight or a DST transition), treat them as durations first, then apply the duration to the start time. Do not add the clock times directly.
For more worked examples, see the How to Add Hours and Minutes guide.
How to Subtract One Time from Another
Subtraction also requires borrowing, but you borrow 60 minutes (not 10) from the hour column.
Step-by-step example: Subtract 4:40 PM from 9:15 AM (same day).
- Convert to 24-hour clock for clarity: 09:15 and 16:40.
- Subtract minutes: 15 - 40 is negative. Borrow 1 hour (60 minutes) from the hour column.
- Now you have 08:75. Subtract: 75 - 40 = 35 minutes.
- Subtract hours: 8 - 4 = 4 hours.
- Result: 4 hours 35 minutes.
What if the end time is earlier than the start time? That means the duration crosses midnight. Add 24 hours to the end time before subtracting. Example: 10:00 PM to 2:00 AM next day becomes 22:00 and 26:00. Subtract: 26:00 - 22:00 = 4 hours.
See the Subtract Time guide for borrowing across multiple columns.
How many hours from Tuesday 8:30 AM to Thursday 5:15 PM?
Use the subtraction method above for same-day or next-day durations. For multi-day spans, calculate the remaining time on the first day, then add full days.
Example: From 8:30 AM Tuesday to 5:15 PM Thursday.
- From 8:30 AM Tuesday to midnight: 15 hours 30 minutes.
- Wednesday: 24 hours.
- Thursday from midnight to 5:15 PM: 17 hours 15 minutes.
- Total: 15h 30m + 24h + 17h 15m = 56 hours 45 minutes.
For precise age or date differences, use the Duration Calculator or the Days Between Dates page.
What are 15, 30 and 45 minutes in decimal hours for payroll?
Decimal hours are common in payroll, billing, and project tracking. The rule: divide minutes by 60.
| Minutes | Decimal hours |
|---|---|
| 5 | 0.08 |
| 10 | 0.17 |
| 15 | 0.25 |
| 20 | 0.33 |
| 25 | 0.42 |
| 30 | 0.50 |
| 35 | 0.58 |
| 40 | 0.67 |
| 45 | 0.75 |
| 50 | 0.83 |
| 55 | 0.92 |
Example: 2 hours 30 minutes = 2 + (30 ÷ 60) = 2.50 decimal hours.
Exact fractions: 1 minute = 0.0167 hours (1/60). 7 minutes = 0.1167 hours (7/60). 13 minutes = 0.2167 hours (13/60). Most payroll systems round to 2 decimal places.
For the full conversion chart, visit Minutes to Decimal Hours page.
How to turn 3.75 on a timesheet back to clock time
Multiply the decimal portion by 60.
Example: 3.75 hours = 3 hours + (0.75 × 60) = 3 hours 45 minutes.
| Decimal hours | Minutes |
|---|---|
| 0.25 | 15 |
| 0.33 | 20 |
| 0.50 | 30 |
| 0.67 | 40 |
| 0.75 | 45 |
| 0.83 | 50 |
| 0.92 | 55 |
Common mistake: 0.5 hours is 30 minutes, not 50 minutes. 1.5 hours is 1 hour 30 minutes, not 1 hour 50 minutes.
How to Calculate Elapsed Time Across Days
The rule: 60 seconds = 1 minute; 60 minutes = 1 hour; 24 hours = 1 day.
For durations longer than 24 hours: 1. Convert everything to minutes or hours first. 2. Divide by 24 to get days. Remainder is hours and minutes.
Example: 50 hours 15 minutes. - 50 ÷ 24 = 2 days (48 hours) with 2 hours 15 minutes remaining. - Result: 2 days, 2 hours, 15 minutes.
When DST changes matter: A day with a "spring forward" has 23 hours. A "fall back" day has 25 hours. For most elapsed-time calculations, you want the clock duration, not the calendar duration. If your calculation crosses a DST transition, use the Elapsed Time Calculator which accounts for the change.
Quick Reference: Time Units and Conversions
| Unit | Equivalent |
|---|---|
| 1 minute | 60 seconds |
| 1 hour | 60 minutes, 3600 seconds |
| 1 day | 24 hours, 1440 minutes |
| 1 week | 7 days |
| 1 month | 28-31 days (varies) |
| 1 year | 365 days (366 in leap year) |
Decimal hours rules: - To change minutes to decimal hours: divide by 60. - To change decimal hours to minutes: multiply by 60. - 0 minutes = 0.00 decimal hours.
Base-60 system: Unlike base-10 arithmetic where you carry at 10, time calculations carry at 60 (minutes) and 24 (hours). Always check your carry and borrow steps when adding or subtracting manually.