How to use it· 4 steps
- Choose 12-hour or 24-hour time, then type the start and end times. 9:30, 930, 9.30 pm and 21:30 all work.
- In 12-hour mode set AM or PM beside each time, or type am or pm after it; the line under each field confirms how it was read.
- Add an unpaid break in minutes if it should come off, then read the result in h:mm, decimal hours and minutes.
- Use “Add & subtract time” to total several durations, or “Decimal ↔ h:mm” to convert hours for payroll.
Step by step
How to use the hours calculator
- 1Choose 12-hour or 24-hour time, then type the start and end times. 9:30, 930, 9.30 pm and 21:30 all work.
- 2In 12-hour mode set AM or PM beside each time, or type am or pm after it; the line under each field confirms how it was read.
- 3Add an unpaid break in minutes if it should come off, then read the result in h:mm, decimal hours and minutes.
- 4Use “Add & subtract time” to total several durations, or “Decimal ↔ h:mm” to convert hours for payroll.
How the time between two clock times is worked out
Each time is converted to minutes after midnight and the start is subtracted from the end. 9:00 AM is 540 minutes and 5:30 PM is 1,050, so the span is 510 minutes: 8 hours 30 minutes, or 8.5 hours. An unpaid break is then taken off — a 30-minute lunch leaves exactly 8 hours.
When the end time is earlier than the start, the span crosses midnight and the end is read as the next day: 10:00 PM to 6:30 AM is 8 hours 30 minutes, worked out as 6:30 + 24:00 − 22:00. The result says when this has happened, so an AM/PM slip is easy to spot. Equal start and end times give zero, not 24 hours; a full-day span is better entered as two parts.
The 12-hour clock has one trap that catches everyone eventually. 12:00 AM is midnight, at the start of the day, and 12:00 PM is noon. In 24-hour time they are 00:00 and 12:00, which is why rotas and timetables often prefer it. Switching the clock setting converts the times you have already entered, so nothing changes meaning when you switch.
Decimal hours, and why 7:45 is not 7.45
Payroll and invoicing systems want hours as a decimal, and minutes become a decimal by dividing by 60: 45 minutes is 0.75 of an hour, so 7 hours 45 minutes is 7.75 hours. Typing 7.45 instead is a classic error — it silently drops 18 minutes, 0.30 of an hour, from the timesheet, and over a month of shifts that is real money.
The common values are worth knowing by heart: 15 minutes is 0.25, 30 is 0.5, 45 is 0.75, 20 minutes is 0.333… and 40 minutes is 0.667. Six minutes is exactly 0.1 of an hour, which is why some employers and law firms record time in tenths. The converter tab includes a table of these, and converts any decimal back the other way: 7.3 hours is 7 hours 18 minutes, because 0.3 × 60 = 18.
Thirds of an hour do not come out evenly in decimals. 20 minutes rounds to 0.33, and 0.33 × 60 is 19.8 minutes, so a system that stores hours to two decimals can be a fraction of a minute out on every entry. The tools here keep exact minutes and only round the figure they display.
Adding and subtracting durations
Durations add like any other numbers once seconds carry into minutes and minutes into hours. 2:45 + 1:30 − 0:20 is 3:55 — the 75 minutes from the first two become 1 hour 15, and the 20-minute subtraction comes off the end. The add-and-subtract tab does the carrying for any number of rows, each marked to add or subtract.
Fields accept more than the clock allows: 90 minutes is simply 1:30:00, and 1.5 in the hours box is 1 hour 30 minutes. Totals above 24 hours stay in hours — 26:05 rather than wrapping round to 2:05 — with the equivalent in days alongside, because a total of working time should not quietly lose a day.
Typical uses are adding up a week of logged sessions, the running time of several videos, flight legs or a project's time entries, and subtracting a pause from a total.
What clock arithmetic does not know
This is arithmetic on clock readings, so it knows nothing about calendars or time zones. A night shift that spans the change to or from daylight-saving time is an hour longer or shorter than the clock difference suggests, and a span between two cities needs both times in the same zone first. For spans of several days, the date difference calculator counts calendar days properly.
For a whole week of shifts — clock-in and clock-out each day, breaks, overtime after 40 hours, and gross pay — use the time card calculator, which builds on the same arithmetic and exports a CSV.
All of it runs in your browser. Times you enter are not sent or stored, and the page works offline once it has loaded.
Answers
Frequently asked questions
How do I calculate the hours worked between two times?
Subtract the start time from the end time, then take off any unpaid break. 8:15 AM to 4:45 PM is 8 hours 30 minutes; less a 30-minute lunch, 8 hours.
How do I convert minutes to decimal hours?
Divide the minutes by 60. 45 minutes is 0.75 hours and 20 minutes is 0.333 hours, so 7 hours 45 minutes is 7.75 hours.
What if a shift goes past midnight?
Enter the times as they are. When the end is earlier than the start, the calculator treats the end as the next day and says so in the result.
Is 12:00 PM noon or midnight?
12:00 PM is noon and 12:00 AM is midnight. In 24-hour time they are 12:00 and 00:00.
How do I add hours and minutes together?
Use the “Add & subtract time” tab: enter each duration in hours, minutes and seconds, mark any that should be subtracted, and read the total.
Does it account for daylight saving time?
No. It works on clock readings, so a span across a daylight-saving change will be an hour out. Adjust one of the times by an hour if your shift crossed the change.