How do I calculate elapsed time?

Subtract the start time from the end time. If the end time is earlier than the start time, add 24 hours to account for a midnight crossing. Convert the result to hours, minutes, and seconds by dividing and using the remainder (modulo) method.

How do you calculate time between two times?

Convert both times to 24-hour format, then subtract start from end. For example, from 9:00 AM to 5:30 PM: convert to 09:00 and 17:30, subtract to get 8:30, which is 8 hours and 30 minutes. Add 24 hours to the end time if it is less than the start time.

What is elapsed time?

Elapsed time is the amount of time that passes between a start event and an end event. It is measured from the moment the clock starts to the moment it stops. Elapsed time and duration mean the same thing — both describe the span of time between two moments.

How does the calculator handle midnight crossings?

If the end time is earlier than the start time, the calculator automatically adds 24 hours to the end time before calculating. For example, a shift from 10:00 PM to 6:00 AM is treated as 10:00 PM to 30:00 (6:00 AM next day), giving an 8-hour duration.

Can I calculate time over multiple days?

This calculator handles up to 24 hours — a single midnight crossing. For durations longer than 24 hours, multiply the number of full days by 24 hours and add the remaining hours, minutes, and seconds manually.

What's the difference between duration and elapsed time?

Duration and elapsed time are synonyms — both refer to the span of time between two moments. "Duration" is often used for scheduled events (the duration of a meeting), while "elapsed time" is more common in timekeeping and performance contexts (elapsed time of a race).

How do you calculate working days between two dates?

To count business days (excluding weekends): subtract the start date from the end date, then subtract the number of Saturdays and Sundays in the range. For example, Monday to Friday of the same week = 5 calendar days, 5 business days. Monday to the following Monday = 8 calendar days, 6 business days. For holidays, subtract any public holidays that fall on weekdays in the range. This time duration calculator handles clock-based durations; for calendar day counting, use a business day calculator.

How many working days are in a year?

A standard US working year has approximately 260 working days (52 weeks × 5 days). Subtracting 11 federal holidays gives about 249 working days. With typical 2-week (10-day) vacation, the average employee works about 239 days per year. Some industries round to 250 working days for planning purposes. This figure matters for calculating hourly rates from annual salary: $52,000 ÷ 2,080 hours (52 weeks × 40 hours) = $25/hour.

What is ISO 8601 duration format?

ISO 8601 is an international standard for representing dates and durations. Duration format is P[Y]Y[M]M[D]DT[H]H[M]M[S]S — for example, P1Y2M3DT4H5M6S means 1 year, 2 months, 3 days, 4 hours, 5 minutes, 6 seconds. The "P" stands for "Period," and "T" separates date components from time components. ISO 8601 durations appear in software APIs, calendar systems, and data interchange formats. For everyday use, HH:MM:SS is more readable.

Time Duration Calculator — Hours, Minutes & Seconds

How to Use This Time Duration Calculator

The time duration calculator on this page finds elapsed hours, minutes, and seconds between any two times. Enter your start and end time using the dropdowns, choose 12-hour or 24-hour format, and instantly see the elapsed time plus the total in decimal hours, total minutes, and total seconds. If your end time is earlier than your start time, the calculator automatically assumes the duration crosses midnight. For tracking hours across multiple days, also see our time card calculator.

How to Calculate Time Duration

The formula for time duration is straightforward: subtract the start time from the end time, converting to a common unit (total seconds) first.

Step-by-Step Formula

Convert start time to total seconds: (H × 3600) + (M × 60) + S
Convert end time to total seconds the same way
Subtract start seconds from end seconds
If the result is negative (crosses midnight), add 86,400 seconds (24 hours)
Convert back: hours = ⌊total ÷ 3600⌋, minutes = ⌊(remainder) ÷ 60⌋, seconds = remainder

Example: 9:15 AM to 5:45 PM

Start: 9 × 3600 + 15 × 60 = 33,300 seconds. End: 17 × 3600 + 45 × 60 = 63,900 seconds. Difference: 63,900 − 33,300 = 30,600 seconds = 8 hours 30 minutes.

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Common Time Duration Examples

Here are some frequently calculated durations:

9:00 AM to 5:00 PM — 8 hours 0 minutes (standard workday)
8:30 AM to 4:30 PM — 8 hours 0 minutes (with same lunch deduction)
7:00 AM to 3:30 PM — 8 hours 30 minutes
10:00 PM to 6:00 AM — 8 hours 0 minutes (overnight/midnight crossing)
1:00 PM to 1:00 AM — 12 hours 0 minutes

For payroll purposes, it is common to convert the duration to decimal hours — for example, 8 hours 30 minutes = 8.50 hours. Use our time to decimal calculator for that conversion. If any hours in your shift qualify as overtime, our time and a half calculator will compute the overtime pay rate.

How to Calculate Elapsed Time Across Midnight

When a shift or event spans midnight, the end time will appear earlier than the start time. The trick is to add 24 hours (86,400 seconds) to the end time before subtracting. For example:

Start: 11:00 PM (23:00), End: 7:00 AM (07:00)
End is earlier, so add 24h: 7:00 AM becomes 31:00 (07:00 + 24:00)
Duration: 31:00 − 23:00 = 8 hours

This calculator handles midnight crossings automatically — just enter the real start and end times and it will detect the crossing.

Time Duration vs. Elapsed Time

The terms "time duration" and "elapsed time" are interchangeable in everyday use. Both describe the span of time between two specific moments. "Duration" is typically used to describe the length of a scheduled event (a 90-minute movie, a 3-hour exam), while "elapsed time" is more common in measurement contexts (elapsed time of a race, time elapsed since an event started). Mathematically, both are calculated the same way. When a duration spans multiple time zones — such as an international flight — use our time zone converter to reconcile local times before computing the difference.

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Time Duration Formula Summary

The core formula used by this calculator:

Total seconds = (endH × 3600 + endM × 60 + endS) − (startH × 3600 + startM × 60 + startS)
If total seconds < 0, add 86,400 (midnight crossing)
Hours = Math.floor(totalSeconds ÷ 3600)
Minutes = Math.floor((totalSeconds mod 3600) ÷ 60)
Seconds = totalSeconds mod 60
Decimal hours = totalSeconds ÷ 3600

Need to track durations across multiple shifts or days? Our average time calculator can find the mean of several time values — useful for averaging shift lengths or meeting durations.

Sources & References

NIST Time and Frequency Division — National Institute of Standards and Technology
International System of Units (SI) — NIST

Time Duration Calculator

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