TimerPlanTime calculator
Time calculator
Resulting time
—
Times roll over midnight, and the day counter says how far.
- Other clock format—
- Day—
- Length—
- In decimal hours—
One thing a month worth timing
MonthlyOne thing a month worth measuring or capping with a clock — a payroll trap, a nap length, a meeting that never gets added up. Two sentences and the tool.
Try also
How do you add time to a time of day?
The TimerPlan time calculator adds or subtracts a length from a clock time by converting both to minutes, doing the arithmetic there and converting back — which is why 9:45 plus 30 minutes comes out as 10:15 rather than 9:75. Clock time is base sixty, and every mistake in this subject comes from treating it as decimal.
Type the length however you say it: 45m, 90 min, 1h 30m, 2:15. Type the time as 9:15 am,
09:15 or 0915.
Answers arrive in both clock formats at once, so a result read by someone who thinks in 24-hour time and someone who thinks in AM and PM does not need translating. When the sum crosses midnight the day counter says so — a two-hour meeting starting at 11:30 pm ends at 1:30 am the next day, and a calculator that returns only the time has told you half the answer.
Everything below is understood in the two boxes:
| Field | Accepted |
|---|---|
| Time | 9:15 am · 09:15 · 0915 · 9am · 21:15 |
| Length | 45m · 90 min · 1h 30m · 1:30 · 90 (seconds) |
A worked example, because it is the case that goes wrong most often: a shift starting at 10:30 pm with eight hours and thirty minutes to run ends at 7:00 am — the next day. The time alone says 7:00, and only the day counter tells you which morning to be there.
For the gap between two times rather than a time plus a length, use the time duration calculator; with a break and a number of days it becomes the hours calculator, and a whole week of them is the time card calculator. For the same arithmetic across countries, the time zone converter works out today’s offset rather than assuming last year’s.
Frequently asked questions
Why is 9:45 plus 30 minutes not 9:75?
Because an hour has sixty minutes, so the minutes column carries at sixty rather than at a hundred. Written down that is obvious; typed into a spreadsheet that treats 9.45 as a decimal number it is not, which is why adding times in a spreadsheet without formatting the cells as time is one of the most reliable ways to produce a wrong answer that looks tidy.
Can I add two lengths together rather than a time and a length?
For lengths alone the seconds to minutes converter is the better page, since it handles unit conversion at the same time. This page is built around a time of day, which is the case that needs the base-sixty carry and the midnight rollover — adding 40 minutes to 25 minutes needs neither.
What does the day counter mean?
How many days the answer sits away from the start. Zero is the same day, plus one is tomorrow, minus one is yesterday. It matters more than it sounds: a night shift, a long-haul flight and a batch job that starts at 11 pm all produce answers on another date, and the time alone reads as though nothing happened.
Does it handle daylight saving?
No, deliberately — this is arithmetic on a clock face, not on a calendar. On the two days a year when the clocks change, a real elapsed hour and a clock hour are not the same thing, and the answer here follows the clock. When the question involves a date and a place, the time zone converter is the tool that knows about daylight saving, because it asks the browser’s zone database rather than assuming.
How this works
Worked example
With Start time 9:15 am, Operation Add Subtract Add, Length 45m, this page works out —. Times roll over midnight, and the day counter says how far.
Sources:
The three traps
Base sixty. Minutes carry at 60, not at 100. Spreadsheets forget this; calculators should not.
Midnight. An answer with no day attached is only half an answer.
Twelve o’clock. 12:00 AM is midnight, 12:00 PM is noon — the reverse of what most people guess, and worth checking before sending a meeting invitation.