Time Duration Calculator: Time Between Two Dates or Two Times

This time duration calculator finds the exact span between two points in time. Use Between Two Times for same-day intervals (e.g., 9:00 AM to 5:30 PM) or Between Two Dates for spans that cross midnight or cover multiple days. The result is displayed in days, hours, minutes, and seconds, plus decimal-day and decimal-hour equivalents for payroll and billing systems. If the end time is before the start time in same-day mode, the calculator assumes an overnight span and adds 24 hours automatically, so 11 PM to 7 AM correctly shows 8 hours. Reversed dates are handled gracefully: you still get the correct absolute duration with a note that the inputs were swapped. A Now button fills either field with the current time or datetime so you can log the moment without looking at a clock. Click Copy Result to export the full breakdown for timesheets, invoices, or project reports.

The calculator converts both timestamps to milliseconds, computes the absolute difference, and divides to get total seconds. The core formula: $\text{Duration (s)} = |\text{End}_{\text{ms}} - \text{Start}_{\text{ms}}| \div 1000$. From total seconds, days are $\lfloor s \div 86400 \rfloor$, remaining hours are $\lfloor (s \bmod 86400) \div 3600 \rfloor$, and so on for minutes and seconds. Decimal forms divide total seconds directly: $\text{Decimal hours} = s \div 3600$ and $\text{Decimal days} = s \div 86400$. For same-day mode, if the end time is earlier than the start, 24 hours (86,400 seconds) are added to the end before subtraction, matching overnight shift logic. For multi-day mode, full calendar dates are used so month and year boundaries are handled correctly.

Select your mode: Between Two Times for intervals within a single day, or Between Two Dates for spans that cross midnight or cover multiple days. In same-day mode, set the start and end times using the hour, minute, second, and AM/PM selectors, overnight shifts where end is before start are detected automatically and show the correct duration. In multi-day mode, use the datetime pickers to choose start and end dates and times. Click the Now button on either field to fill it with the current time or datetime, which is useful when logging a task you just finished. The results panel shows the duration in days, hours, minutes, and seconds, plus Total Days (Decimal) and Total Hours (Decimal) for payroll or billing verification. Click Copy Result to paste the full breakdown, duration, decimal days, decimal hours, total minutes, and total seconds, into a timesheet, invoice, or report.

Duration is the difference between two points in time. The core formula is $\text{Duration (seconds)} = |\text{End}_{\text{ms}} - \text{Start}_{\text{ms}}| \div 1000$; from total seconds, we derive days, hours, minutes, and seconds. Decimal forms: $\text{Days} = \text{seconds} \div 86{,}400$ and $\text{Hours} = \text{seconds} \div 3{,}600$.

Many timesheet systems use decimal hours: $1\text{ h }45\text{ m} = 1 + \frac{45}{60} = 1.75\text{ hours}$. Billing 1h 45m as 1.45 would underpay; 1.75 is correct. This calculator outputs Total Hours (Decimal) and Total Days (Decimal) so you can verify payroll or project billing.