How to calculate overtime hours on shift work
Short answer: overtime = hours actually worked − hours scheduled (or your contract limit) for the period. Log the extra time on the day it happens, not from memory at month end.
1. Get the scheduled hours from your rotation
Multiply shifts by length. On a 4 on 4 off rotation with 12-hour shifts you work about 15 shifts in a 30-day month: 15 × 12 = 180 scheduled hours.
2. Log the extra time each day
Stayed 1.5 hours for handover? Write +1.5h on that date. Half-hour steps are accurate enough for most rosters.
3. Separate swaps, leave and sick days
A traded shift moves hours, it doesn't add them. Vacation and sick days reduce worked hours. Keep them apart so the overtime number stays honest.
4. Compare with your contract
Some workplaces count overtime per day (over 8 or 12 hours), others per week (over 40) or per pay period. Apply your rule to the totals.
Doing it with Dutymark
Set your rotation once, then tap any date to add overtime in half-hour steps, record a swap or mark leave. The month summary shows hours worked and overtime side by side.
FAQ
How do I count overtime on 12-hour shifts?
Count scheduled hours from your rotation, add every extra half hour you stayed, and compare the total with your contract hours for the pay period.
Should a shift swap count as overtime?
Usually not. A straight trade moves hours between days. Only extra hours beyond your schedule are overtime, but check your employer's rules.
Is this the same as my payslip?
No. Overtime pay rules differ by employer and country. Use your own log to check the payslip, not to replace it.