Duration Calculators & Timers
Five tools for a length of time rather than a date — adding up hours, converting a span between units, and timing something live.
Adding up hours is base 60, not base 10
Timesheets are where this bites: 7 hours 45 minutes plus 6 hours 30 minutes is 14 hours 15 minutes, not 13.75 plus 6.5 typed into whatever is nearest. The Time Duration adds and subtracts times properly and gives the total in hours and minutes as well as decimal hours — the decimal form being what payroll and invoicing systems usually want, and the form most likely to be mis-entered by hand.
Converting a span between units
How many weeks is 18 months? How many years is 30 months? The Time Unit Converter and the Months, Weeks & Years convert a span between months, weeks and years, which comes up in pregnancy tracking, child development, loan terms and notice periods. Be aware that a month is not a fixed number of weeks — the conversion uses the average month of about 4.35 weeks, so a figure in weeks will differ slightly from counting a specific calendar span with the Date Difference.
Counting down and timing live
The Countdown Timer counts down to a moment you set and the Stopwatch counts up from when you start it, both running in your browser with nothing stored on a server. They are the two tools here that are not arithmetic at all — use them for cooking, workouts, presentations, exams and anything else where the useful thing is watching the number move.
Which tool for which question
If the answer you want is a date, use the date calculators linked above. If it is a length of time, it is one of these. And if the length of time is a deadline measured in business days rather than raw hours, go back to the Working Days — the two are easy to mix up on a project plan.
Frequently asked questions
Why can I not just add times as decimals?＋
Because time is base 60. Two hours forty-five minutes is 2.75 hours as a decimal but 2:45 on a clock, and adding 2:45 to 1:30 gives 4:15, not 3.75 of anything. Mixing the two notations mid-calculation is the most common source of wrong timesheet totals.
Should I use a timer or a stopwatch?＋
A timer counts down to a moment you have chosen and is the right tool for a deadline, a rest interval or anything with a fixed end. A stopwatch counts up from now and is the right tool when you want to know how long something took. If you are recording several stages of one activity, the stopwatch’s lap function keeps them together.
Do these keep running if I switch tabs?＋
They stay accurate, which is not quite the same as staying running. Browsers throttle background tabs, so the display may not repaint every second — but the elapsed and remaining figures are recomputed from the clock rather than counted, so the moment you return the number shown is correct.
How do I convert a duration into decimal hours for payroll?＋
Divide the minutes by sixty and add them to the hours: 7 hours 30 minutes is 7.5, and 7 hours 20 minutes is 7.33 recurring. The duration calculator shows both forms, because timesheets are usually kept in clock time and paid in decimal.