Hours Calculator

How to calculate hours between two times

Convert both times to the 24-hour clock, subtract, and read the answer as hours and minutes:

duration = end − start

17:30 − 09:00 is 8 hr 30 min. Working in 24-hour form is not a stylistic preference — it removes the two places where hour arithmetic usually goes wrong, which are 12 AM and 12 PM. When the end time is earlier on the clock than the start, the shift crossed midnight, and the formula becomes:

duration = (24 h − start) + end

For 23:00 to 07:00 that is 1 hour to midnight plus 7 hours after it, so 8 hours. This calculator makes that reading visible rather than silent, because an unannounced overnight assumption is indistinguishable from a bug.

How to calculate work hours

Worked time is not the same as the interval between the first clock-in and the last clock-out. Add every work period, then take off the breaks that are unpaid:

worked time = Σ work intervals − unpaid breaks

A day of 08:00–12:00 and 13:00–17:00 is two intervals of four hours, so eight hours of work time. Flattening it into a single 08:00–17:00 entry and then guessing at an hour of break gives the same answer here by luck and a different answer the moment the lunch is 45 minutes. Paid breaks are deducted from nothing: they are inside the paid day, so the calculator totals them separately and leaves worked time alone.

How to convert hours and minutes to decimal hours

Timesheets and payroll systems usually want a decimal, not a clock reading:

decimal hours = hours + minutes ÷ 60 + seconds ÷ 3600

7 hr 45 min is 7 + 45 ÷ 60 = 7.75. The failure this prevents is writing 7 hr 45 min as “7.45”, which is 18 minutes short and looks entirely plausible on a form. Going the other way — hours to minutes — is a multiplication by 60, so 7.75 hours is 465 minutes. The reference table below is generated by that same division.

How to add and subtract hours

Add hours to hours and minutes to minutes, then carry each 60 minutes into an hour. 2 hr 45 min + 1 hr 30 min is 3 hr 75 min, which carries to 4 hr 15 min — 4.25 decimal hours, 255 minutes, 15,300 seconds. Subtraction is the same operation with a negative sign, so 8 hr 30 min − 1 hr 45 min = 6 hr 45 min. Internally every row becomes an integer number of seconds before anything is added, which is why a long list of rows cannot accumulate rounding drift.

Overnight shifts

A shift that starts at 10:00 PM and ends at 6:00 AM is eight hours, and the only reason it is awkward is that the clock resets in the middle of it. There are exactly two honest ways to handle it: detect that the end is earlier than the start and say so, or let the user state that the end is on the next day. This calculator does both, and keeps them apart, because of one case that separates a careful tool from a careless one: 09:00 to 09:00. On the same day that is zero hours. With the next-day control set it is 24 hours. A calculator that quietly turns the first into the second has converted a typo into a full day of pay.

12-hour vs 24-hour time

12-hour time needs AM and PM to be unambiguous, and its two edge values are the ones people get wrong: 12:00 AM is midnight (00:00) and 12:00 PM is noon (12:00). 24-hour time — the same clock people call military time when it is written without a colon, as 0900 or 1730 — has no such ambiguity, which is why this engine normalizes to it before any arithmetic runs. The format selector on the calculator changes the display only; you can type 9:00 AM, 09:00 or 0900 interchangeably and all three become the same integer internally.

Decimal hours for timesheets and payroll

Payroll multiplies a rate by a number, so it needs 7.75 rather than 7:45. Two habits make decimal hours safe: convert from the exact minute count rather than from an already-rounded clock reading, and keep enough precision to survive a week of additions. This calculator derives every decimal figure from the same integer second count that produces the hours-and-minutes figure beside it, so the two can never disagree — a mismatch there is one of the most common defects in hour calculators, and it is the kind that survives review because both numbers look right on their own.

Exact time vs rounded payroll time

Exact is the default here. If your workplace rounds, two things matter. First, which operation is being rounded: rounding each clock entry to the nearest quarter hour is a different calculation from rounding the finished duration, and the two produce different totals often enough that stating which one you mean is part of the answer. A punch at 9:07 rounds down to 9:00 at a 15-minute increment, while 9:08 rounds up to 9:15 — and applying that to both ends of a shift is not the same as taking the elapsed time and rounding once. Second, rounding is a policy question, not an arithmetic one: whether it is permitted, and in whose favour, is set by law and contract. The calculator will apply the increment you choose and show it as its own line in the receipt, so a rounded figure is never mistaken for a measured one.

Hours from now and hours ago

“What time will it be in eight hours?” is a question about an instant, not about a clock face. Adding eight hours to a clock reading of 10:44 PM gives 6:44, but only adding to a real instant tells you it is 6:44 AM the next morning — and only that approach survives a daylight-saving change on the night in question. The From Now / Until mode reads your device's clock when the page loads, adds the offset to that instant, and shows the resulting time, weekday and date along with the time zone it used. You can also count from a date and time you choose, or count down to one.

Duration versus calendar time, and daylight saving

Seventy-two elapsed hours and three calendar days are the same thing for most of the year and different twice a year. In a zone that observes daylight saving, a local midnight-to-midnight “day” is 23 hours when the clocks go forward and 25 hours when they go back, even though the calendar shows one day in both cases. Undated clock times carry no time zone at all, so the question never arises for a plain start-and-end calculation. As soon as you add dates, this calculator resolves both ends to real instants, computes elapsed time as a subtraction of instants, and reports the calendar figure separately whenever the two disagree.

A worked reference case, computed by the shipped engine at build time: from 2026-03-08T01:30:00−05:00 to 2026-03-08T03:30:00−04:00 the wall clock advances two hours, but the true elapsed time is 1 hr 00 min, because the offset changed from −05:00 to −04:00 in between. That vector is part of the engine's test suite, not a claim in prose.

Hours in a day, week, month and year

A day is 24 hours and a week is 168. A month has no single number of hours, and any calculator that gives one is rounding a calendar into a rule. February alone can be 672 or 696 hours.