β±οΈ Clock Duration Calculator
Exact time between two clock times, overnight spans included.
Duration
How to Use This Calculator
Type the start and end times in either 12-hour format ("2:45 PM") or 24-hour format ("14:45"), then hit Calculate Duration. The tool returns hours and minutes as the headline, with total minutes and decimal hours underneath. If the end time is earlier than the start time, it assumes the span crossed midnight and says so explicitly: 10:00 PM to 6:00 AM reads as 8 hours overnight. Both times accept seconds too, though most people never need them.
Enter the start time. "9:15 AM" and "09:15" both work.
Enter the end time. Earlier than start means overnight; the tool flags it.
Hit Calculate Duration and read hours and minutes plus the decimal for payroll.
Subtract breaks separately for paid hours; this tool measures gross clock time.
The Method: Minutes Since Midnight
Minutes-since-midnight is the only method that never needs borrowing, because the subtraction happens once on plain numbers. The AM/PM conversion is where humans fail: 12:30 AM is 30 minutes past midnight, not 12 hours 30 minutes, and 12:45 PM is 765 minutes, not 45. The overnight rule (add a full day to the end time when it precedes the start) matches how people actually mean it: nobody saying "10 PM to 6 AM" means negative 16 hours. Decimal hours come last: divide leftover minutes by 60. The number 5.5 means 5 hours 30 minutes; 5.3 would mean 5 hours 18 minutes, which is why decimal timesheets punish sloppy conversion.
Worked Example
A night-shift nurse clocks in at 10:30 PM and out at 6:45 AM. Start = 22 x 60 + 30 = 1,350 minutes. End = 6 x 60 + 45 = 405 minutes, which is less than start, so add 1,440: 1,845. Duration = 1,845 - 1,350 = 495 minutes = 8 hours 15 minutes = 8.25 decimal hours. Enter those times and the calculator reproduces it, labeled overnight. A day-shift check: 9:15 AM (555) to 2:45 PM (885) = 330 minutes = 5 hours 30 minutes, no rollover needed.
The 12 AM / 12 PM Trap
Noon and midnight break everyone's intuition because 12 behaves like 0 in the 12-hour system. Midnight is 12:00 AM, the start of the day; noon is 12:00 PM, the middle. The mnemonics that work: AM means "after midnight has started," so 12 AM begins the day; PM means "past midday," so 12 PM begins the afternoon. Scheduling disasters live here: "12:00 AM Friday" means Thursday night turning into Friday, and meeting invites get this wrong constantly. When precision matters, write "midnight Friday" or use 24-hour time: 00:00 and 12:00 are unambiguous.
From Duration to Paycheck
Duration is gross time; pay is net. Subtract unpaid meal breaks from the gross: 8.5 hours on site minus 30 minutes unpaid equals 8 paid hours. Track the distinction daily, because most wage disputes are really duration-versus-paid-hours disputes. Weekly overtime in the US triggers after 40 hours, so five 8.25-hour days is 41.25 hours with 1.25 at time-and-a-half. Some states add daily overtime: California pays 1.5x after 8 hours in a day. The duration calculator gives you the raw material; the time card calculator turns it into dollars.
Billing Hours and Invoicing
Freelancers and consultants live by duration math: every invoice is a list of time spans turned into money. The professional standard is billing in tenths of an hour (6-minute increments), which is why lawyers' timesheets read 0.3, 1.2, 2.7. Compute the exact duration with this calculator, convert to decimal hours, and round per your policy stated up front: rounding up to the next tenth is standard, rounding to the quarter is common in trades. Log start and stop times contemporaneously; reconstructed timesheets inflate, usually unintentionally. Separate billable from non-billable explicitly: the client pays for the work, not your learning curve on their problem. And invoice promptly: same-week invoices get paid faster than month-end batches, because the work is fresh in the client's mind and the amount feels expected rather than surprising.
Broadcast and Event Scheduling
Radio, TV, and live events run on ruthless duration math: every segment has a hard out-time, and the show hits it or bleeds into the next program. Producers work backward from the hour: a 42-minute content hour means 18 minutes of ads and breaks, placed at fixed slots. Compute each segment's duration, cumulative runtime, and the float available for overruns. Live events add setup and teardown spans that amateurs forget: the wedding is 4 hours, but the venue booking is 8 with setup, photos, and breakdown. This calculator's overnight handling matters for events crossing midnight: the after-party ending at 2 AM started the previous calendar day. Build the run-of-show as a table of start times and durations, and the event manages itself.
A Second Worked Example: The Split Shift
Work 9:00 AM to 1:00 PM, break, then 5:00 PM to 9:00 PM. Morning: 1:00 PM is minute 780, 9:00 AM is 540, difference 240 minutes, 4 hours. Evening: 9:00 PM is 1,260, 5:00 PM is 1,020, difference 240 minutes, 4 hours. Total: 8 hours. The gap between shifts never enters the math; only time on the clock counts. Two clean calculations, one addition, no midnight wrap needed because neither span crosses it.
Split shifts are where the "subtract breaks separately" advice proves itself. The four-hour gap is unpaid time off, not a break within a shift. Treat each block as its own duration, then add. Combining them into one span and subtracting the gap works mathematically but confuses everyone who reads the timesheet later.
Why Computers Get Time Wrong
Time math looks trivial until daylight saving enters. A duration from 1:30 AM to 3:00 AM on the spring-forward night is 30 minutes of real elapsed time, not 90, because the clock skips an hour. On the fall-back night the same clock span is 2 hours 30 minutes of real time. Scheduling software earns its keep on exactly these two nights a year, and every payroll system has scar tissue from them.
The reliable solution, used by every serious system, is to compute in UTC or in absolute timestamps and convert to local time only for display. If you are building anything that tracks hours across a DST boundary, store the timestamps, not the clock readings. And never schedule recurring events in local time across a transition without checking: the 2:30 AM backup job either runs twice or never, depending on the night.
Common Duration Mistakes
First: the 12 problem. 12:30 AM is 00:30, just after midnight. 12:30 PM is 12:30, just after noon. Twelve belongs to the hour that follows it in spirit but precedes it on the clock, and it causes more errors than every other hour combined. Convert to 24-hour time when it matters: 00:30 and 12:30 cannot be confused.
Second: forgetting the overnight wrap. Any end time earlier than the start crossed midnight; add the day. Third: reading decimal hours as hours and minutes. 8.5 is 8:30; 8.3 is 8:18. Fourth: adding durations as decimals. 1:30 plus 1:30 is 3:00, not 2.60. Fifth: trusting the phone's calculator app with time arithmetic. It does decimal math beautifully and time math not at all; that is what this calculator is for.
Frequently Asked Questions
How long is it from 9:15 AM to 2:45 PM?
5 hours 30 minutes. Subtract the start from the end: 14:45 minus 9:15. When the minutes need borrowing, take 60 from the hours. Enter both times above and the calculator handles the borrowing, the AM/PM conversion, and overnight spans automatically.
How do you calculate duration across midnight?
Add 24 hours to the end time when it is earlier than the start time. From 10:00 PM to 6:00 AM: treat 6:00 AM as 30:00, subtract 22:00, and get 8 hours. The calculator detects overnight spans on its own and labels the result so you can see the rollover happened.
What is the duration in decimal hours?
Hours plus minutes divided by 60. A 5 hour 30 minute duration is 5.5 hours; 7 hours 45 minutes is 7.75. Payroll and billing systems use decimals, so the calculator shows the decimal equivalent under every result. Never type 5.30 for 5 hours 30 minutes; that means 5 hours 18 minutes in decimal.
How do I handle AM and PM correctly?
Convert to 24-hour time first: PM hours add 12 (except 12 PM, which stays 12), and 12 AM becomes 0. So 2:45 PM is 14:45 and 12:30 AM is 00:30. The classic error is treating 12 PM as 24 or forgetting 12 AM is midnight. The calculator accepts both formats and converts internally.
Can duration be negative?
Only if you intend it. If the end time is earlier than the start, the calculator assumes overnight and gives a positive span. If you truly need a negative difference, like comparing planned versus actual, use the add/subtract hours calculator instead. For clock times, overnight assumption is right 99 percent of the time.
How do I calculate work hours with this?
Enter clock-in and clock-out times for the gross duration, then subtract unpaid breaks separately. A 9:00 AM to 5:30 PM span is 8.5 hours; minus a 30-minute lunch gives 8 paid hours. For weekly totals with overtime math, the time card calculator picks up where this one leaves off.
Why do my manual time subtractions keep failing?
Two culprits: the 60-minute borrow and the 12 AM/PM trap. People subtract 9:45 from 10:15 and get 0:30 by luck, then try 9:45 to 10:05 and write 0:40 instead of 0:20 because they subtracted minutes left to right. Always borrow properly or let the calculator do it.
What is the total minutes shortcut?
Convert both times to minutes since midnight, then subtract: 2:45 PM is 885 minutes, 9:15 AM is 555, and 885 - 555 = 330 minutes, which is 5 hours 30 minutes. This minutes-since-midnight method is how the calculator works internally, and it is the most reliable mental method too.