3 on 3 off is a 6-day cycle: three 12-hour shifts, then three days off, repeat. The cycle is one day shorter than the week, so every block starts one weekday earlier than the last. A Monday start becomes a Sunday start, then a Saturday start, and the whole pattern walks backward through the week until it comes home six weeks later.
We make Lumical, an app that scans work rosters into your calendar, so read this with that in mind. Everything below is calendar math you can check on our free shift pattern visualizer.
How the 3 on 3 off shift pattern drifts
A 6-day cycle and a 7-day week only line up every 42 days. That window holds exactly seven work blocks, seven off blocks, and six weekends, then everything repeats. Whatever the pattern does to you in one six-week stretch, it does forever.
The backward walk surprises people coming from 4 on 4 off, which drifts the other way: its 8-day cycle starts each block one weekday later. Neither direction is better. Both just mean your days off never sit still, and no crew stays stuck with the bad weekends.
Where the weekends land
Lay out any 42-day round and the six weekends always split the same way:
- Two are fully off, and they arrive back to back.
- Two are fully worked.
- Two are split: you work Saturday or Sunday but not both.
So one weekend in three is clear, and roughly every third off block covers a full Saturday and Sunday. The rhythm is lumpy though: a pair of free weekends, then four weeks before the next pair. How many free weekends that adds up to in a given year depends on where your rotation sits in January, so the 3 on 3 off calendar for 2026 counts them for your exact starting position, and the 2027 calendar is there when your roster rolls over.
That is the day-shift picture. On nights it tightens. The first of your three off days is a recovery day (you get home in the morning and sleep through most of it), and a Friday night shift runs into Saturday morning, which spoils that weekend even though Saturday is off on paper. The visualizer marks both.
The 42 hour average week
Three 12-hour shifts per 6-day cycle is 36 hours. Scale that to a 7-day week and you get 42, which is the number contracts usually quote. No single week actually contains it. A calendar week holds either three of your shifts (36 hours) or four (48 hours), and the drift serves them in runs: three heavy weeks, then three light ones.
Across a year you work half of all days, which comes to 182 or 183 shifts and about 2,190 hours. That is the same annual load as 4 on 4 off. The hours just arrive in shorter bites. Whether those hours count as overtime or attract shift premiums varies by contract and country, so check yours rather than trusting a blog post.
3 on 3 off vs 2 on 2 off vs 4 on 4 off
All three patterns work half the days in 12-hour shifts, so all three average 42 hours a week. What changes is the texture.
| Pattern | Cycle | Longest run | Off block | Lines up with the week |
|---|---|---|---|---|
| 2 on 2 off | 4 days | two 12s | 2 days | every 4 weeks |
| 3 on 3 off | 6 days | three 12s | 3 days | every 6 weeks |
| 4 on 4 off | 8 days | four 12s | 4 days | every 8 weeks |
2 on 2 off never asks for more than two 12s in a row, but it never hands back more than two days either, and the first of those often goes on sleep and laundry. 4 on 4 off demands four straight shifts and pays for it with a four-day break you can plan something around. 3 on 3 off sits between them: one more shift in a row than 2 on 2 off, one fewer than 4 on 4 off, with a break to match. The math does not pick a winner here. It only tells you the price of each trade.
Putting a 3 on 3 off schedule in your calendar
A clean 3 on 3 off is easy to project forward. Mark out 42 days once and copy the block. Real rosters rarely stay clean: a swap, a training day mid-block, overtime on your first off day, all handed to you as a printed grid or a photo in the group chat. That gap between the pattern and the paper is where hand-typing goes wrong, usually on the overnights.
This is the part Lumical is built for. It reads the photo of your roster, understands the rotation, and files every shift on the correct days, overnights included. You review everything it found before it saves.
Working 3 on 3 off from a printed roster? Get Lumical on the App Store and put the whole rotation in your calendar from one photo.