Time Duration Calculator
Find the elapsed time between two clock times or two dates and times, in hours, minutes and seconds, with decimal hours and every step shown.
Seconds are optional, as in 9:15:30. A time such as 17:45 or 24:00 is read on the 24 hour clock.
From 9:15 AM to 5:45 PM on the same day.
Measured on one 24 hour clock. For spans longer than a day, switch to dates and times.
In hours, minutes or seconds
Use decimal hours for pay, invoices and spreadsheets, and minutes or seconds for timers and logs.
Your calculation
The same steps the calculator runs, with your numbers.
- Start 9:15 AM (09:15): 9 × 3,600 + 15 × 60 = 33,300 s after midnight.
- End 5:45 PM (17:45): 17 × 3,600 + 45 × 60 = 63,900 s after midnight.
- Difference: 63,900 − 33,300 = 30,600 s.
- Split: 30,600 ÷ 3,600 = 8 h, remainder 1,800 s; 1,800 ÷ 60 = 30 min, remainder 0 s = 8 h 30 min.
- Decimal hours: 30,600 ÷ 3,600 = 8.5 h.
Span on a 24 hour clock
Shaded: 9:15 AM to 5:45 PM.
Rounded for a timesheet
The total rounded to common timekeeping steps. Your employer's policy decides how real punches are rounded.
| Rounding | h:mm | Decimal hours |
|---|---|---|
| Nearest 5 minutes | 8:30 | 8.5 |
| Nearest 6 minutes (0.1 h) | 8:30 | 8.5 |
| Nearest 15 minutes (0.25 h) | 8:30 | 8.5 |
Wall clock arithmetic in whole seconds. Time zones and leap seconds are not included.
How the Time Duration Calculator Works
This time duration calculator measures the elapsed time between a start and an end: either two clock times on the same day or overnight, or two full dates with times. It returns the duration in hours, minutes and seconds, together with decimal hours, total minutes, total seconds, a clock style h:mm:ss value and an ISO 8601 duration code. Every step uses whole seconds, so no rounding happens until the final decimal figures.
The method is the one you would use on paper. Each time becomes a count of seconds after midnight, the start is subtracted from the end, and the difference is split back into hours, minutes and seconds.
In the dates and times mode the calculator also counts the whole days between the two dates and adds 86,400 seconds for each one. It works on wall clock time, the times printed on a clock, ticket or schedule, which is what most people mean by elapsed time. Daylight saving changes and time zones are covered further down this page.
How to Calculate Time Difference in Hours and Minutes Manually
You can subtract times by hand without converting everything to seconds. Write both times on the 24 hour clock, then subtract minutes from minutes and hours from hours, the same way you subtract columns of ordinary numbers.
- Convert to 24 hour time. Add 12 to any PM hour from 1 PM to 11 PM, keep 12 PM as 12 and write 12 AM as 0. So 5:45 PM becomes 17:45.
- Subtract the minutes. If the end minutes are smaller than the start minutes, borrow one hour from the end time and add 60 to its minutes.
- Subtract the hours. What remains is the duration in hours and minutes.
- Fix an overnight result. If the end hour is smaller than the start hour, add 24 to the end hour before you subtract.
Borrowing example: a shift from 8:45 to 16:10. The end minutes, 10, are smaller than 45, so borrow one hour and 16:10 becomes 15:70. Then 70 − 45 = 25 minutes and 15 − 8 = 7 hours, for a duration of 7 hours 25 minutes, or 26,700 seconds.
Seconds work the same way, with 60 seconds borrowed from a minute when needed. For a race that starts at 1:02:15 PM and finishes at 3:47:40 PM, subtract column by column: 40 − 15 = 25 seconds, 47 − 2 = 45 minutes and 15 − 13 = 2 hours. The race lasted 2:45:25, which is 9,925 seconds or 2.7569 hours.
Hours Between Two Times Overnight and Across Dates
A clock time alone does not say which day it belongs to. When the end time is earlier on the clock than the start time, the calculator assumes the period crosses midnight once and ends the next day, which fits night shifts, sleep and late events. It adds 86,400 seconds, the length of one day, and labels the result Crosses midnight.
The same rule covers short spans around midnight: 11:30 PM to 12:15 AM is 45 minutes, not 23 hours 15 minutes. Two identical times give zero, because a clock time cannot show whether a full day passed in between.
For anything longer than 24 hours, or whenever the dates matter, use the dates and times mode. It counts calendar days with UTC date arithmetic, so month lengths and leap years are handled, and then adds the difference between the clock times.
If the end date and time come before the start, the result shows the size of the gap and marks it End before start, so a swapped pair of dates still gives a usable answer.
12 Hour and 24 Hour Clock: Midnight and Noon
Many mistakes with elapsed time come from 12 AM and 12 PM. In common use, and in this calculator, 12:00 AM is midnight at the start of the day (00:00) and 12:00 PM is noon (12:00). The National Institute of Standards and Technology (NIST) notes that both labels are technically ambiguous, since noon is neither before nor after noon. It suggests the 24 hour clock for clarity, with 00:00 for the midnight that starts a date and 24:00 for the midnight that ends it.
| 12 hour clock | 24 hour clock | Seconds after midnight |
|---|---|---|
| 12:00 AM (midnight) | 00:00 | 0 |
| 12:30 AM | 00:30 | 1,800 |
| 6:00 AM | 06:00 | 21,600 |
| 11:59 AM | 11:59 | 43,140 |
| 12:00 PM (noon) | 12:00 | 43,200 |
| 12:30 PM | 12:30 | 45,000 |
| 6:00 PM | 18:00 | 64,800 |
| 11:59 PM | 23:59 | 86,340 |
| Midnight, end of day | 24:00 | 86,400 |
Type a time such as 17:45 and the calculator reads it on the 24 hour clock even when AM or PM is selected, because 17 cannot be a 12 hour value. You can also enter 24:00 as an end time to measure up to the end of a day: 9:00 AM to 24:00 is 15 hours.
Convert Hours and Minutes to Decimal Hours
Payroll, invoicing and spreadsheets usually need a duration in decimal hours, because 8.5 can be multiplied by an hourly rate while 8:30 cannot. Divide the minutes by 60 and add them to the whole hours, and divide any seconds by 3,600.
Minutes to decimal hours chart
| Minutes | Decimal hours | Minutes | Decimal hours |
|---|---|---|---|
| 1 | 0.0167 | 30 | 0.5 |
| 5 | 0.0833 | 36 | 0.6 |
| 6 | 0.1 | 40 | 0.6667 |
| 10 | 0.1667 | 42 | 0.7 |
| 12 | 0.2 | 45 | 0.75 |
| 15 | 0.25 | 48 | 0.8 |
| 18 | 0.3 | 50 | 0.8333 |
| 20 | 0.3333 | 54 | 0.9 |
| 24 | 0.4 | 55 | 0.9167 |
| 25 | 0.4167 | 59 | 0.9833 |
Values with a repeating decimal, such as 20 minutes (0.3333 and so on), appear to four places here and in the results. Rounded to two places, 20 minutes becomes 0.33 hours, which drops 0.0033 hours, about 12 seconds, on every entry.
The results also include a rounding table for timesheets. The U.S. Department of Labor rule at 29 CFR 785.48 accepts recording start and stop times to the nearest 5 minutes, tenth of an hour or quarter hour, provided the practice does not underpay employees over time. The table applies those steps to the total as a guide.
Seconds in a Minute, Hour, Day, Week and Year
| Period | Seconds | Minutes | Hours |
|---|---|---|---|
| 1 minute | 60 | 1 | 0.0167 |
| 1 hour | 3,600 | 60 | 1 |
| 1 day | 86,400 | 1,440 | 24 |
| 1 week | 604,800 | 10,080 | 168 |
| 365 day year | 31,536,000 | 525,600 | 8,760 |
| 366 day leap year | 31,622,400 | 527,040 | 8,784 |
The second is the base unit. NIST explains that it is defined by counting 9,192,631,770 oscillations of the microwave radiation that cesium atoms absorb and emit. Coordinated Universal Time (UTC) occasionally inserts a leap second, so a rare UTC day lasts 86,401 seconds; so far leap seconds have always come at the end of June or December. The calculator, like ordinary clocks and timesheets, treats every day as 86,400 seconds.
ISO 8601 duration format
ISO 8601 is the international standard for writing dates, times and time intervals. A duration starts with P, for period, and T separates the date part from the time part, so 8 hours 30 minutes is PT8H30M and 2 days 2 hours 15 minutes is P2DT2H15M. The grammar in Appendix A of RFC 3339 lists the same pieces: H for hours, M for minutes and S for seconds after the T, and a zero duration can be written PT0S.
A day written with D is a calendar day, so software that needs an exact count of hours often prefers PT50H15M over P2DT2H15M. The ISO 8601 tile in the results shows the hours form, with the days form underneath once the span reaches 24 hours.
Daylight Saving Time and Elapsed Time
On two nights a year, local clocks in most of the United States skip or repeat an hour. NIST lists the 2026 changes as Sunday, March 8 at 2:00 AM, when clocks jump to 3:00 AM, and Sunday, November 1 at 2:00 AM, when clocks fall back to 1:00 AM. The schedule comes from federal law, 15 U.S.C. 260a, which runs daylight saving time from the second Sunday of March to the first Sunday of November; in 2026 that is 238 days.
| Period on a US local clock | Clock difference | Real elapsed time |
|---|---|---|
| Sat, Mar 7, 2026 10:00 PM to Sun, Mar 8, 6:00 AM | 8 h | 7 h |
| Sat, Mar 7, 2026 9:00 PM to Sun, Mar 8, 9:00 AM | 12 h | 11 h |
| Sat, Oct 31, 2026 10:00 PM to Sun, Nov 1, 6:00 AM | 8 h | 9 h |
The calculator reports the clock difference, which is what a schedule or timecard shows. In the dates and times mode it checks whether the span crosses 2:00 AM on a US change date, using the rule in force since 2007. When it does, a chip appears and the line under the answer gives the real elapsed time. Places that do not observe daylight saving time, such as Hawaii and most of Arizona, can ignore that note.
How to Use the Calculator
- Pick a mode. Two times covers a span within one day or overnight. Dates and times covers longer spans.
- Enter the start and end. Type 9:15, 9:15:30 or 17:45, then choose AM, PM or 24 h beside each time. Typing pm in the box works too.
- Use Now to fill in the current time from your device, and today's date in the dates mode.
- Read the answer. The top card shows hours and minutes, the next card decimal hours, minutes and seconds, and the steps show the arithmetic.
Common Mistakes
- Treating 12 AM as noon. 12:30 AM to 1:00 PM is 12 h 30 min, because 12:30 AM is just after midnight.
- Reading 8.30 hours as 8:30. 0.30 × 60 = 18, so 8.30 hours is 8 h 18 min.
- Subtracting clock times as decimals. 11.15 − 9.45 = 1.70, but 11:15 − 9:45 is 1 h 30 min.
- Ignoring the date. An earlier end time means the next day. Use dates for longer gaps.
- Mixing time zones. Convert both times to one zone first.
Related Time Calculations
This page measures a single span between two moments. To add or subtract durations, such as 3 hours 20 minutes plus 45 minutes, use the Time Calculator, and to convert many entries between hours and minutes and decimal hours, use the Hours Calculator. The Time Card Calculator totals a weekly timesheet with breaks, overtime and pay. For whole days, the Day Counter counts the days between two dates, the Date Calculator adds or subtracts days, and the Age Calculator gives an exact age in years, months and days.
Common uses for an elapsed time calculator include checking a timecard, billing a client by the hour, logging how long a process ran, timing a race or workout from start and finish clock times, measuring how long you slept, and finding the gap between two log timestamps.
Frequently Asked Questions
How do I calculate the time duration between two times?
Convert both clock times to the 24 hour clock, then to seconds after midnight: hours × 3,600 plus minutes × 60 plus seconds. Subtract the start from the end. If the result is negative, the span crosses midnight, so add 86,400 seconds, the length of one day. Divide by 3,600 for whole hours, divide the remainder by 60 for minutes, and keep what is left as seconds. Example: 9:15 AM is 33,300 seconds and 5:45 PM is 63,900 seconds, so 63,900 − 33,300 = 30,600 seconds, which is 8 hours 30 minutes.
How many hours are between two times overnight?
When the end time is earlier on the clock than the start time, the period runs past midnight into the next day, so add 24 hours to the end time before you subtract. For a night shift from 10:00 PM to 6:30 AM, write the times as 22:00 and 6:30, add 24 hours to get 30:30, then subtract: 30:30 − 22:00 = 8 hours 30 minutes. In seconds the same step is 23,400 − 79,200 = −55,800, and −55,800 + 86,400 = 30,600 seconds. A span longer than 24 hours needs the dates as well as the times.
How do you convert hours and minutes to decimal hours?
Divide the minutes by 60 and add the result to the whole hours. For 7 hours 20 minutes, 20 ÷ 60 = 0.3333, so the duration is 7.3333 hours, or 7.33 hours rounded to two places. For 8 hours 45 minutes, 45 ÷ 60 = 0.75, giving 8.75 hours. Include seconds by dividing them by 3,600. To go back, multiply the decimal part by 60: 0.75 × 60 = 45 minutes. Payroll and billing systems use decimal hours because they multiply cleanly by an hourly rate, while a value like 7:20 cannot be multiplied directly.
Is 12:00 AM midnight or noon?
In everyday use 12:00 AM means midnight at the start of a day and 12:00 PM means noon, and this calculator follows that convention: 12:00 AM is 00:00 and 12:00 PM is 12:00 on the 24 hour clock. NIST points out that both labels are technically ambiguous, because noon is neither before nor after noon. For contracts and schedules it suggests writing 11:59 PM or 12:01 AM, or using the 24 hour clock, where 00:00 is midnight at the start of a date and 24:00 is midnight at its end. You can enter 24:00 as an end time here.
Does daylight saving time change the elapsed time?
Yes, on the one night in spring and the one night in autumn when clocks change. In the United States in 2026, clocks jump from 2:00 AM to 3:00 AM on Sunday, March 8, and fall back from 2:00 AM to 1:00 AM on Sunday, November 1. A shift from 10:00 PM to 6:00 AM on those nights lasts 7 real hours in March and 9 in November, although the clock difference is 8 hours. This calculator measures wall clock time; in the dates and times mode it flags spans that cross a US change and states the real elapsed time.
Sources & References
- National Institute of Standards and Technology. Times of Day FAQs (12 a.m. and 12 p.m., midnight as 0000 and 2400), updated October 11, 2024. nist.gov
- National Institute of Standards and Technology. Daylight Saving Time Rules (2026 dates, spring forward and fall back). nist.gov
- Legal Information Institute, Cornell Law School. 15 U.S. Code § 260a, Advancement of time or changeover dates. law.cornell.edu
- National Institute of Standards and Technology. Second: Introduction (cesium definition of the second). nist.gov
- National Institute of Standards and Technology. Leap Seconds FAQs. nist.gov
- International Organization for Standardization. ISO 8601, Date and time format. iso.org
- Klyne, G. and Newman, C. RFC 3339, Date and Time on the Internet: Timestamps, Appendix A (ISO 8601 duration grammar), IETF, 2002. RFC Editor
- Legal Information Institute, Cornell Law School. 29 CFR § 785.48, Use of time clocks (rounding practices). law.cornell.edu
Results are wall clock calculations for planning, scheduling and study. For payroll, legal deadlines or travel records, follow the official rules that apply to you. Every number on this page was recomputed with the same arithmetic the calculator uses. Methodology reviewed: 2026.