Free elapsed time calculator
Time Duration Calculator
Find the elapsed time between two clock readings. Use 12-hour or 24-hour time, handle overnight and multi-day intervals, deduct a break and view exact totals.
Last Updated: July 24, 2026
Calculate Time Between Two Times
Enter a start and end. Use explicit dates for intervals longer than one day or whenever the calendar date matters.
A time duration calculator finds the elapsed time between a start clock reading and an end clock reading. It answers questions such as “How long is 9:15 AM to 5:45 PM?” and “How many hours pass from 10:30 PM to 6:15 AM?” Enter a break only when it should be removed from the elapsed interval.
This tool accepts 12-hour time with AM and PM or 24-hour time. Clock-only mode handles intervals within one 24-hour cycle. Date mode calculates a longer span from an explicit start date and time to an explicit end date and time. Results include normalized days, hours, minutes and seconds plus decimal-hour, minute, second and day totals.
How to Use the Time Duration Calculator
- Select Clock times only for a same-day or overnight interval. Select Dates and clock times for a multi-day interval.
- Choose 12-hour or 24-hour time. The tool converts existing entries when you switch formats.
- Enter the start hour, minute and second. In 12-hour mode, select AM or PM.
- Enter the end clock reading in the same way.
- For clock-only mode, choose the overnight rule. Automatic mode moves the end to the next day only when it is earlier than the start.
- Add an optional break in hours, minutes and seconds. Leave all three break fields at zero when no deduction applies.
- Select the number of decimal places used to display seconds, then select “Calculate Duration.”
- Review gross elapsed time, the deducted break, net duration and totals in common units.
What the Calculator Measures
Elapsed time is the amount of time between two instants. In a simple same-day example, subtract the start clock reading from the end clock reading. An overnight interval needs one extra day. A multi-day interval also needs the calendar-day difference.
The calculator keeps gross and net duration separate:
- Gross elapsed time is the complete interval from start to end.
- Break deducted is the entered non-working, paused or excluded duration.
- Net duration is gross elapsed time minus the break.
The fixed unit relationships follow the NIST SI reference: one minute equals 60 seconds, one hour equals 3,600 seconds and one 24-hour day equals 86,400 seconds.
Time Duration Formula
Each clock reading is first converted to seconds after midnight. A 24-hour clock reading of 17:45:00 becomes 17 × 3,600 + 45 × 60 = 63,900 seconds after midnight.
For an overnight clock-only interval, 86,400 seconds are added when the end reading is earlier than the start. In date mode, the number of elapsed calendar days is multiplied by 86,400 before the clock difference is added. The script uses integer milliseconds so seconds entered to three decimal places remain stable.
Worked Example: 9:15 AM to 5:45 PM
Assume the start is 9:15 AM, the end is 5:45 PM and the break is 30 minutes.
- 9:15 AM in 24-hour time is 09:15.
- 5:45 PM in 24-hour time is 17:45.
- Gross elapsed time is 17:45 − 09:15 = 8 hours 30 minutes.
- Net duration is 8 hours 30 minutes − 30 minutes = 8 hours.
- Eight hours equals 480 minutes, 28,800 seconds or 0.333333 of a 24-hour day.
The decimal-hour result is 8.0. Without the break, 8 hours 30 minutes would equal 8.5 decimal hours, not 8.30.
How Overnight Time Is Calculated
An end reading earlier than the start often means the interval crossed midnight. For example, 10:30 PM to 6:15 AM has a gross duration of 7 hours 45 minutes. Automatic mode recognizes this because 6:15 AM is earlier on the clock than 10:30 PM and places the end on the next day.
Use the overnight setting deliberately:
- Automatic: use the next day only when the end is earlier. Equal times mean zero.
- Same day: reject an end that is earlier than the start. This helps catch an accidental AM/PM entry.
- Next day: always place the end on the following day. Equal readings then equal 24 hours.
If the interval lasts more than 24 hours, use explicit dates. A clock reading alone cannot distinguish 6 hours from 30 hours when both start and end show the same times of day.
Using Dates for Multi-Day Duration
Select “Dates and clock times” when the start and end are on known calendar dates. This removes the one-day ambiguity. For example, July 24 at 8:00 PM to July 26 at 2:00 AM is 30 hours before any break deduction.
Date mode treats each elapsed day as 24 hours. It calculates wall-clock duration and does not apply a geographic time zone or daylight-saving transition. A named local time zone is essential when a real interval crosses a clock change or when start and end occur in different locations.
12-Hour and 24-Hour Time
In 12-hour time, 12:00 AM is midnight and 12:00 PM is noon. These two boundary readings cause many manual errors. In 24-hour time, midnight starts at 00:00 and noon is 12:00. Times after noon continue from 13:00 through 23:59.
| 12-hour reading | 24-hour reading | Meaning |
|---|---|---|
| 12:00 AM | 00:00 | Midnight, start of a day |
| 9:15 AM | 09:15 | Morning |
| 12:00 PM | 12:00 | Noon |
| 5:45 PM | 17:45 | Afternoon or evening |
| 11:59 PM | 23:59 | One minute before midnight |
Time Duration and Decimal Hours
Clock minutes use base 60. Decimal hours use base 10. Divide minutes by 60 before adding them to whole hours. This matters for time records, project logs and pay estimates.
| Clock duration | Decimal hours | Calculation |
|---|---|---|
| 15 minutes | 0.25 | 15 ÷ 60 |
| 30 minutes | 0.50 | 30 ÷ 60 |
| 45 minutes | 0.75 | 45 ÷ 60 |
| 8 hours 18 minutes | 8.30 | 8 + (18 ÷ 60) |
| 8 hours 30 minutes | 8.50 | 8 + (30 ÷ 60) |
Keep the unrounded result for calculations. Round only the final display when a form, invoice or reporting system requires a set precision. An employer may also apply a separate payroll-rounding policy, so a mathematical duration does not by itself determine paid hours.
When to Deduct a Break
A break should be entered only when it falls inside the start-to-end interval and must be excluded. If a task ran from 1:00 PM to 4:00 PM with a 20-minute pause, gross duration is 3 hours and net duration is 2 hours 40 minutes.
The calculator rejects a break longer than the gross interval. It allows a break equal to the gross time, which produces zero net duration. For several shifts, multiple breaks, daily overtime or payroll rounding, calculate each interval under the governing policy instead of merging unrelated records.
Common Uses
- Measure a meeting, class, appointment or examination.
- Find travel time when departure and arrival use the same local clock rules.
- Calculate machine runtime, downtime or a service window.
- Check a single work interval before using an Overtime Pay Calculator.
- Convert project time into decimal hours before estimating an hourly freelance rate.
- Compare a measured weekly schedule with an hourly-to-salary estimate.
Common Time Difference Errors
Reversing AM and PM
12:00 AM is midnight, while 12:00 PM is noon. Convert to 24-hour time when a result looks 12 hours too high or too low.
Ignoring midnight
Subtracting 22:30 from 06:15 produces a negative clock difference. If the end is next morning, add one 24-hour day or use Automatic overnight mode.
Treating minutes as hundredths
Six hours 45 minutes equals 6.75 hours. It does not equal 6.45 hours. Divide the minute portion by 60.
Deducting a break twice
Do not enter a break if the recorded start and end already exclude it. Confirm whether the source record shows gross attendance or net working time.
Using wall-clock math across time zones
Two identical clock readings can represent different instants in different locations. Convert both instants to the same time zone before comparing them.
Time Duration Calculator vs Time Calculator
These tools answer different questions. A time duration calculator compares start and end clock readings. A time calculator adds or subtracts duration quantities such as 2 hours 40 minutes plus 1 hour 35 minutes. Use the Date, Time & Age directory to choose the correct method.
| Question | Correct tool type | Key input |
|---|---|---|
| How long from 9:15 AM to 5:45 PM? | Time Duration Calculator | Start and end clock readings |
| What is 2 hours 45 minutes plus 1 hour 30 minutes? | Time Calculator | Two duration quantities |
| What is 7 hours 45 minutes as a decimal? | Time-to-Decimal Calculator | One duration and output format |
| How many hours did I work across several days? | Timesheet Calculator | Several shifts and breaks |
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Frequently Asked Questions
How do I calculate the duration between two times?
Convert both clock readings to seconds after midnight, subtract the start from the end and convert the result back to hours, minutes and seconds. Add one day when the interval crosses midnight.
How does the calculator handle an overnight interval?
Automatic mode treats an earlier end reading as occurring on the next day. You may instead force the same day, force the next day or enter explicit dates.
What happens when the start and end times are equal?
With a zero break, Automatic and same-day modes return zero. Select the next-day option when equal readings represent a complete 24-hour interval.
Does the calculator support both 12-hour and 24-hour time?
Yes. You may enter time with AM and PM or use hours from 00 through 23. Switching the format preserves valid clock entries.
How do I subtract a lunch or rest break?
Enter the break in the separate hours, minutes and seconds fields. The result shows gross elapsed time, break deducted and net duration.
Can I calculate a duration longer than 24 hours?
Yes. Select “Dates and clock times,” then enter the start and end dates. Clock-only mode is limited to a same-day or next-day interval.
Does the result account for time zones or daylight saving time?
No. Date mode uses 24-hour wall-clock days. Convert both instants to one time zone or use a location-aware tool when an interval crosses zones or a daylight-saving change.
What is the difference between a Time Duration Calculator and a Time Calculator?
A Time Duration Calculator finds elapsed time between start and end clock readings. A Time Calculator adds or subtracts duration quantities such as hours, minutes and seconds.
Is 8 hours 30 minutes equal to 8.30 decimal hours?
No. Thirty minutes is 30 divided by 60, or 0.5 hour. Therefore, 8 hours 30 minutes equals 8.5 decimal hours.
Disclaimer: This calculator provides mathematical wall-clock results for general planning. It does not determine wages, overtime, attendance, legal deadlines, billing rights, transport schedules or time-zone adjustments. Verify dates, locations, source records, break rules and applicable policies before using a result for a formal decision.