An overnight shift can produce a negative result if you subtract clock readings without their dates. For an ordinary night, split the shift at midnight or add 24 hours to the following day's finish time.
From 22:30 to midnight is 1 hour 30 minutes. Midnight to 06:15 adds 6 hours 15 minutes. The total is 7 hours 45 minutes. With a 30-minute unpaid break, the remaining duration is 7 hours 15 minutes, or 7.25 decimal hours.
Another approach is to treat 06:15 the next day as 30:15. Subtracting 22:30 gives the same 7:45 interval. This is an arithmetic aid, not a clock time you should put into a calendar invitation.
Record the start date, end date, and break duration beside each shift. This removes ambiguity when an entry spans more than one night. Subtract only breaks your records classify as unpaid; the calculator cannot decide workplace policy.
Use the standard calculator for minute totals: 7 × 60 + 45 − 30 = 435 minutes. Divide by 60 if a timesheet requests decimal hours.
A daylight-saving transition can make elapsed time differ from the apparent difference between local clock readings. For those nights, use timestamps with the applicable UTC offsets or your timekeeping system's recorded duration. The simple midnight split assumes the clock did not jump forward or backward during the shift.