Time Calculator

A night shift is eight hours, and the arithmetic says minus sixteen

A shift from 22:00 to 06:00 is 8 hours 0 minutes — 480 minutes. Subtract the times directly and you get 6 − 22 = −16 hours, which is the single most common error in any duration calculation.

The problem is that clock time is modular: it wraps at 24 and starts again. Any interval crossing midnight needs 24 hours added back, and this calculator handles that with an explicit "crosses midnight" setting rather than guessing — because 22:00 to 06:00 is a legitimate 8-hour night shift and *also* a legitimate way to express a negative interval, and only you know which you meant.

The two modes

Duration — the gap between two clock times:

Duration = end − start, and if negative, add 24 hours

For the example: 06:00 − 22:00 = −16 hours. Add 24: 8 hours. In minutes, (6 × 60) − (22 × 60) + 1,440 = 360 − 1,320 + 1,440 = 480.

Shift — moving a time forward or backward by an amount, wrapping at midnight. Adding 90 minutes to 23:00 gives 00:30 the following day.

Working in minutes

The reliable way to do any time arithmetic by hand is to convert everything to minutes since midnight first, operate, then convert back:

• 22:00 → 22 × 60 = 1,320
• 06:00 → 6 × 60 = 360
• 360 − 1,320 = −960, add 1,440 → 480 minutes
• 480 ÷ 60 = 8 hours 0 minutes

This avoids the borrow-from-60 mistakes that make manual time subtraction unreliable, and it is exactly what the calculator does internally.

Where it is used

Payroll and shift work — computing hours worked, particularly night shifts and split shifts.

Overtime calculation, where the hours beyond a standard day must be isolated before a multiplier is applied.

Billable time for consultants, lawyers and agencies working to the six-minute or fifteen-minute unit.

Broadcast and production scheduling, where running times must sum exactly.

Travel planning — journey durations, layovers, and connection feasibility.

Cooking, workouts and processes timed to the minute.

Decimal hours, and the conversion that catches people

Payroll systems almost always want decimal hours, not hours and minutes. The conversion is division by 60, not a decimal point shift:

• 8 hours 30 minutes = 8 + (30 ÷ 60) = 8.5
• 8 hours 15 minutes = 8.25
• 8 hours 20 minutes = 8.333, not 8.20
• 8 hours 45 minutes = 8.75

Writing 8 hours 20 minutes as "8.20" in a timesheet underpays by 8 minutes on that entry alone, and the error is invisible because the number looks plausible.

Reading the result

The duration is a clock interval, not paid time. A 22:00 to 06:00 shift is eight hours on the clock and may be seven and a half paid hours once an unpaid break is deducted, or more than eight in pay terms once a night-shift premium is applied.

Note too that this measures wall-clock time, which is not always elapsed real time. A shift spanning a daylight saving transition is 23 or 25 real hours despite the clock showing the usual span — relevant for shift workers in zones observing DST, and for anything billed by actual elapsed time.

Common mistakes

Subtracting without wrapping. Any interval crossing midnight comes out 24 hours short.

Writing minutes as decimals. 8.20 is not 8 hours 20 minutes.

Forgetting unpaid breaks. Clock duration and paid duration differ.

Mixing 12-hour and 24-hour notation. 12:00 AM is midnight and 12:00 PM is noon, which is the reverse of most people's intuition — a large share of scheduling errors trace to exactly this.

Assuming a DST-spanning shift is the usual length. It is an hour longer or shorter in real time.