Why standard calculators fail shift workers
Most salary tools make three assumptions without saying so: the day starts and ends on the same calendar date, a shift is eight hours, and a break sits in the middle of it. Shift work breaks all three.
The midnight crossover is the one that quietly ruins the maths. A 22:00–06:00 shift is eight hours long, but a naive calculator subtracts 22:00 from 06:00 and gets negative four. Some tools clamp that to zero. Some produce a daily rate of nothing. Either way, the number is wrong and nothing warns you.
This calculator detects the crossover from the times themselves: if the end is earlier than the start, the window wraps past midnight. Breaks get the same treatment, so a 02:00 lunch break is placed at hour four of the shift rather than at hour minus twenty.
The maths of a 12-hour rota
Take a typical 3-on-3-off pattern: twelve-hour shifts, three days on, three days off, which averages 3.5 shifts a week. With a 30-minute unpaid break each shift, that is 11.5 paid hours per shift.
| Pattern | Paid hours / shift | Shifts / week | Hours / year | Rate at $60,000 |
|---|---|---|---|---|
| 5 days · 8h paid | 8.0 | 5.0 | 2,080 | $28.85 |
| 3-on-3-off · 12h shift | 11.5 | 3.5 | 2,093 | $28.67 |
| 4-on-4-off · 12h shift | 11.5 | 3.5 | 2,093 | $28.67 |
| 5 days · 12h shift | 11.5 | 5.0 | 2,990 | $20.07 |
The last row is the one that matters. A 12-hour shift five days a week is 57.5 paid hours — a $60,000 salary on that schedule is $20.07 an hour, not $28.85. Same money, 30% less per hour of your life. If you are on that pattern, you are almost certainly underpaid relative to a standard contract, and the number proves it in a way an annual salary never can.
Getting a rota right
- Enter the shift as it runs, not as it is rostered. If you regularly stay 40 minutes for handover and it is unpaid, that is part of the picture — but it is unpaid, so it belongs in your head, not in the paid-hours total. Keep the timer honest.
- Add every unpaid break. Shift work tends to have several short ones rather than one long one. Two 15-minute breaks and a 30-minute meal break is an hour of unpaid time per shift — 3.5 hours a week on a 3.5-shift rota.
- Turn on overtime for night differentials. If your contract pays a premium after a certain hour, the overtime multiplier is the closest available approximation. For an exact figure, set your blended rate instead.
- Update the working days when the rota flips. This is the one field that changes the answer most, because it changes your annual hours.
What to watch on a long shift
On a twelve-hour shift the counter is not a novelty, it is a progress bar for the day. Two useful moments: halfway, which on an 11.5-hour paid shift arrives around hour six, and the last paid hour, which is when the finish line becomes visible and the temptation to stay late gets a price.
If you are comparing two rotas — say 3-on-3-off against a 5-day week at the same salary — run both through the hourly rate calculator before deciding. For the written overview, see the shift work guide, or start from the salary timer homepage.