Time Duration Calculator

Both modes work in plain minutes-since-midnight rather than full calendar dates, which keeps the math simple and avoids time-zone or daylight-saving glitches that can creep in when clock times are converted through Date objects.

Time Difference example: if you clock in at 9:15 AM and clock out at 5:45 PM the same day, the calculator converts both to minutes since midnight (555 and 1065), takes the difference (510 minutes), and displays it as 8 hours 30 minutes.

Crossing midnight: if a shift starts at 10:00 PM and ends at 6:00 AM, the end time is technically earlier in the day than the start time. Ticking “End Time is Next Day” tells the calculator to add a full 24 hours (1,440 minutes) to the end time before subtracting, correctly producing an 8-hour duration instead of a negative or nonsensical result.

Add/Subtract example: starting at 11:30 PM and adding 3 hours 15 minutes rolls past midnight to 2:45 AM, and the tool flags that the result lands on the next day.

This tool is distinct from the Date Calculator, which works in whole calendar days between two dates. This Time Duration Calculator works entirely in clock time — hours and minutes within or across a day — rather than calendar days, months or years.