No fixed cycle. The shift type changes between blocks — days one week, nights the next, or a schedule posted a fortnight at a time with no pattern to it at all. What holds constant is the shape of a block: a run of shifts of one type, then time off, then a run of a different type.
These are example times, not your times. Everything below is computed from a single pair of wake anchors: 3:00 PM on a work day and 8:00 AM on a rest day. A 3:00 PM wake is the harder case — a night block — and the one worth working through. On a day block the same plan runs off an earlier anchor and every window moves with it. If your anchors are different, every window below shifts with them, which is what the plan builder does with your own numbers.
The plan works backward from the wake anchor rather than forward from bedtime, because bedtime is the part your schedule takes away from you. The sleep target on each day is the anchor minus the sleep opportunity; the caffeine cutoff is eight hours before that target; the last real meal is three hours before wind-down starts. So the anchor is the only number you set, and the rest falls out of it.
Every day inside a work block, whichever shift it is. 12 hours on duty, going on shift at 6:00 PM.
| Wake anchor | 3:00 PM |
|---|---|
| Bright light | 3:00 PM to 4:30 PM |
| Caffeine | 4:00 PM to 4:30 PM (first cup), stop by 11:00 PM |
| Planned nap | 7:00 PM to 8:30 PM |
| Last real meal | by 2:30 AM |
| Wind-down | 5:30 AM to 6:00 AM |
| Sleep target | 7:00 AM |
The day the shift type changes.
| Wake anchor | 3:00 PM |
|---|---|
| Bright light | 3:00 PM to 4:30 PM |
| Caffeine | 4:00 PM to 4:30 PM (first cup), stop by 1:00 AM |
| Planned nap | 7:00 PM to 8:30 PM |
| Last real meal | by 4:30 AM |
| Wind-down | 7:30 AM to 8:00 AM |
| Sleep target | 9:00 AM |
Days outside any work block.
| Wake anchor | 8:00 AM |
|---|---|
| Bright light | 8:00 AM to 9:30 AM |
| Caffeine | 9:00 AM to 9:30 AM (first cup), stop by 4:00 PM |
| Last real meal | by 7:30 PM |
| Wind-down | 10:30 PM to 11:00 PM |
| Sleep target | 12:00 AM |
A fixed pattern gives you one thing an irregular one does not: a wake anchor that means the same thing next week. Without that, the anchor has to move, and the only structure left to attach it to is the block itself rather than the days of the week. So the plan sets the anchor when the block is posted, holds it for every day inside the block, and changes it only on the changeover. The changeover is where the pattern costs you — it is a sleep aligned to the block you are leaving, followed immediately by a shift belonging to the block you are entering. The engine builds that day as its own type: a shorter sleep aligned to where you are going, with the light window right after it doing the work of pulling the clock along.
When the schedule changes constantly, the anchor moves with the work block instead of with the days of the week. Set it as soon as you know the block, hold it for every day inside the block, and change it only on the changeover day. On the changeover, take a shorter sleep aligned to the new block rather than a full sleep aligned to the old one, and get bright light immediately after waking to pull the clock with you.
Eight hours before the sleep opportunity you are protecting. In the worked example on this page, a 3:00 PM wake anchor on a work day puts the sleep target at 7:00 AM, so the last caffeine of any kind lands at 11:00 PM. Move the anchor and the cutoff moves with it — the eight hours is the rule, not the clock time.
The plan sets the sleep target backward from the wake anchor rather than forward from the end of a shift. In the example here, a 3:00 PM work-day anchor gives a 7:00 AM sleep target, with wind-down starting at 5:30 AM. On a rest day the 8:00 AM anchor gives a 12:00 AM target.
Within 90 minutes of waking, whatever the sun is doing. In the worked example that is 3:00 PM to 4:30 PM on a work day. Ten to fifteen minutes is enough. Then keep bright light off you in the three hours before the sleep target.
One nap, taken on purpose, four to five and a half hours after waking — 7:00 PM to 8:30 PM in the worked example on this page. Twenty to thirty minutes, or a full ninety. Anything in between leaves you groggy.
Rotation change is planned as its own kind of day rather than a normal one. In the example, it runs on a shorter sleep opportunity ending at 3:00 PM, with the caffeine cutoff at 1:00 AM and the last real meal by 4:30 AM.
The plan builder takes six questions — your pattern, your two wake times, your last cup of coffee — and computes the same windows against the schedule you actually work, as a visual timeline for each kind of day. Free, printable, no account.
Build my free sleep planEvery window on this page comes from one of a handful of rules, and the Shift Worker's Field Manual is where those rules are laid out with their sources: why the wake anchor is the lever rather than bedtime, what light does to the body clock and when, the eight-hour caffeine cutoff and where it comes from, and what to do when the problem is bigger than a schedule.
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