Measure the difference between two datetimes or add a duration forward.
This tool provides estimates for informational purposes only and is not a substitute for professional advice. Individual results vary based on personal circumstances and assumptions.
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Calculating the exact duration between two points in time — or finding the date and time that results from adding a specific interval — is more useful than it sounds. How long was a meeting? How many hours and minutes between a hospital admission and discharge? How long until an event that starts at a specific date and time? What date and time is exactly 72 hours from now? This time duration calculator handles all of these scenarios, including durations that span days, giving you results in days, hours, minutes, and decimal hours.
Time duration is the elapsed time between two specific points in time — a start datetime and an end datetime. Unlike date difference (which counts whole calendar days), time duration includes the time-of-day component and can be expressed in days, hours, minutes, seconds, or any combination.
Examples of time duration questions:
To calculate the duration between two datetimes:
Example: Start: Tuesday March 5 at 14:30. End: Thursday March 7 at 09:15.
The calculator performs this calculation instantly when you enter both datetimes in the "date difference" mode.
The second mode of this calculator does the reverse: given a start datetime and a duration (in days, hours, and minutes), it calculates the resulting end datetime. This is useful for:
Durations can be expressed in many ways. Here are common conversions:
Reference: common durations in multiple units
A business meeting that starts at 09:30 and ends at 12:45: duration = 3 hours 15 minutes = 3.25 decimal hours. For billing purposes, this rounds to 3.25 hours at the applicable rate.
International flights often cross midnight and may involve time zone changes. The calculator gives you the raw elapsed time — the actual time the flight takes regardless of time zone offsets. A flight from London (GMT/BST) to New York takes about 8 hours regardless of the time zone difference.
Length of stay calculations — a patient admitted at 15:00 on Day 1 and discharged at 10:30 on Day 4: duration = 2 days 19 hours 30 minutes = 67.5 hours = 2.8 days. Hospital billing and insurance typically counts "midnights" rather than 24-hour periods.
A slow-cooker recipe requires 8 hours on low. If you start it at 08:30, it will be ready at 16:30. This calculator confirms that by adding 8 hours to the start time.
Many legal deadlines specify hours rather than days. "You have 48 hours from receipt of notice to respond" — if notice was received at 14:30 on Monday, the deadline is 14:30 Wednesday. This calculator gives you the exact end datetime.
For payroll, billing, and reporting purposes, durations are often needed in decimal hours. The conversion: decimal hours = whole hours + (minutes ÷ 60).
When billing clients at an hourly rate, round to two decimal places. For payroll, follow your employer's rounding policy (typically to the nearest 0.1 or 0.25 hours).
Durations that cross midnight require careful handling. If an end time is numerically earlier than a start time — like start 23:00, end 07:00 — the duration is not negative. It means the end time is on the next calendar day. Duration = (24:00 − 23:00) + 07:00 = 1 hour + 7 hours = 8 hours.
For multi-day durations, this calculator uses full datetimes (date + time) rather than just times, which eliminates ambiguity. Always enter the complete date and time for durations that span more than 24 hours.
Enter both datetimes in the start and end fields and select "find difference." The calculator returns the exact duration in days, hours, minutes, and decimal hours.
Date difference counts whole calendar days between two dates. Time duration includes the time-of-day component and is more precise — it can give you hours and minutes, not just days. Use time duration for anything where the time of day matters.
Enter the current date and time as the start, select "add duration" mode, enter 3 days (or 72 hours) in the duration fields, and the result shows the exact future datetime.
4 + (45 ÷ 60) = 4 + 0.75 = 4.75 decimal hours.
Disclaimer: Results are based on calendar dates and do not account for time zone transitions or daylight saving time changes that occur during the duration period. For cross-time-zone durations, use the Time Zone Calculator.