How to use the hours calculator
Enter a start time and an end time. The end-day rule tells the calculator which day the end time belongs to, which is the part people usually get wrong in their heads. Auto works for most cases: a later end time is the same day, and an earlier or equal one is the next day.
Break hours and minutes are subtracted from each interval. The repeat count multiplies the result, which is handy when the same session happens several times. Pick 2, 3 or 4 decimal places for the decimal-hour figure.
- Enter the start time and the end time.
- Pick an end-day rule: Auto, same day, next day, or a custom number of days later.
- Enter any break as hours plus the remaining minutes (0 to 59).
- Set the repeat count if the same interval happens more than once.
- Read the result in hours and minutes, decimal hours, total minutes and seconds.
Hours and minutes calculator examples
A same-day span from 9:00 AM to 5:30 PM is 510 minutes. Take off a 30-minute break and you have 480 minutes, which is 8 hours. Repeat it five times and the total is 40 hours.
An overnight span from 10:00 PM to 6:00 AM is 480 minutes. With a 45-minute break, that leaves 435 minutes, or 7 hours 15 minutes, which is 7.25 decimal hours.
| Times and rule | Clock span | Break | Result |
|---|---|---|---|
| 9:00 AM to 5:30 PM, same day | 8 h 30 min | 30 min | 8 h (8.00) |
| 10:00 PM to 6:00 AM, Auto | 8 h | 45 min | 7 h 15 min (7.25) |
| 9:00 AM to 9:00 AM, same day | 0 h | 0 min | 0 h (0.00) |
| 9:00 AM to 9:00 AM, Auto | 24 h | 0 min | 24 h (24.00) |
Picking the right end-day rule
The same two clock times can mean very different durations. Auto treats an end time that's earlier than or equal to the start as the next day. Same day treats equal times as zero. Next day always moves the end to tomorrow, so 9:00 AM to 5:30 PM becomes 32 hours 30 minutes. Custom adds as many whole days as you enter.
| Rule | 9:00 to 17:30 | 22:00 to 06:00 | 09:00 to 09:00 |
|---|---|---|---|
| Auto | 8 h 30 min | 8 h | 24 h |
| Same day | 8 h 30 min | Not valid (negative) | 0 h |
| Next day | 32 h 30 min | 8 h | 24 h |
| Custom: 2 days | 56 h 30 min | 32 h | 48 h |
Hours calculator formula
Working in minutes avoids the base-60 borrowing that trips people up. Each time becomes minutes after midnight, whole days are added as 1,440 minutes each, and the break comes off before any repeat.
Clock minutes = hours x 60 + minutesSpan = end minutes + days later x 1,440 - start minutesNet minutes = span - break minutesTotal minutes = net minutes x repeat countDecimal hours = minutes / 60
Minutes to hours and decimal hours
To turn minutes into hours, divide by 60. 135 minutes is 2.25 hours, or 2 hours 15 minutes. Clock time and decimal time look alike but aren't the same: 7:30 on a clock means 7 hours 30 minutes, which is 7.50 decimal hours. 7 hours 45 minutes is 7.75, not 7.45.
The calculator shows all three forms side by side, and the minute total stays exact no matter how many decimal places you choose.
| Minutes | Hours and minutes | Decimal hours |
|---|---|---|
| 45 | 0 h 45 min | 0.75 |
| 90 | 1 h 30 min | 1.50 |
| 135 | 2 h 15 min | 2.25 |
| 200 | 3 h 20 min | 3.33 |
| 435 | 7 h 15 min | 7.25 |
| 465 | 7 h 45 min | 7.75 |
Adding hours for repeated sessions
To add up the same duration several times, use the repeat count. Four sessions of 7 hours 45 minutes come to 31 hours. The break is subtracted from each session before they're added together.
The repeat count only multiplies one identical interval. Different durations, such as 2 hours 45 minutes plus 3 hours 30 minutes, need a separate run each. Add the minute totals afterwards, or use the method in our guide to adding hours and minutes. For a full week of different shifts, the work hours calculator takes a separate row for each day.
When to double-check the result
The calculator counts every day as exactly 24 hours and doesn't know dates or time zones. On the night clocks change for daylight saving time, a shift can really be an hour shorter or longer than the clock times suggest. The same goes for flights across time zones.
If the hours affect pay, the arithmetic is only part of the answer. Whether a break is paid, how time is rounded and what counts as overtime all depend on your employer's policy and the rules where you work.
Sources
These references cover time units, standard time notation, daylight saving rules and how work time is defined.