Time Duration Calculator

You started a meeting at 10:42 AM and ended at 1:17 PM. How long was that? 2 hours 35 minutes — an annoying calculation across the hour boundary, especially when one time is AM and the other is PM. Type both, get the duration in hours, minutes, and decimal hours.

Spans across midnight work too: 11:30 PM to 2:15 AM correctly returns 2 hours 45 minutes, not negative 21 hours. Useful for shift workers, billable hours, sleep tracking, and 'how long was that flight, including the time zone change.'

Decimal hours output is what most invoicing and payroll software wants. Hours-and-minutes is what humans actually think in.

The calculation walks through unit conversion: convert both times to a single unit (typically minutes since midnight), subtract, then convert back. Crossing midnight requires the special case of adding 1440 minutes (24 hours) when the end time is numerically less than the start time. So 11:30 PM (1410 minutes) to 2:15 AM (135 minutes) is calculated as 135 + 1440 - 1410 = 165 minutes = 2 hours 45 minutes.

For mixing AM and PM correctly: 10:42 AM to 1:17 PM means 10:42 in the morning to 13:17 in 24-hour terms. 13:17 - 10:42 = 2 hours 35 minutes. The calculator handles AM/PM input automatically, but you can also enter 24-hour times directly to skip the conversion. Decimal hours conversion is then mechanical: 35 minutes / 60 = 0.583, so 2.583 hours decimal. Most invoicing systems want decimal hours, which is why both formats appear in the output.

A worked example for shift workers: you're scheduled 11:30 PM to 7:45 AM. That's 8 hours 15 minutes (11:30 PM to 7:30 AM is exactly 8 hours; add 15 more for 7:45). Decimal: 8.25. If you took a 30-minute meal break, your actual worked time is 7 hours 45 minutes, decimal 7.75. The calculator subtracts breaks if you enter them. Across midnight, across a meal break, with shift differential — these are exactly the calculations that get nuked by hand under fatigue, which is when you most need them right.

Where the calculator stops: anything that spans more than 24 hours. A 30-hour shift can't be expressed as 'start time to end time' on a single day; it's a date-aware question, not a time-aware one. For multi-day durations, you need a date-and-time calculator that handles full timestamps. The calculator pops a warning if the inferred duration approaches 24 hours, which is the threshold where ambiguity creeps in — is '11 PM to 10 PM' a 23-hour duration (next day) or 1-hour backward (impossible)? The calculator assumes forward and adds 24 hours; if you meant something else, switch to a date-aware tool.

A subtle issue with 12:00 AM and 12:00 PM: 12:00 AM is midnight (the start of the day), 12:00 PM is noon. Some people read '12:00 AM' as noon by analogy with PM, get the conversion wrong, and end up 12 hours off. If AM/PM is a regular source of confusion, switch to 24-hour time entry — it removes the ambiguity entirely.