A four-week cycle of twelve-hour shifts: four nights, three days off, three days, one day off, three nights, three days off, four days, then seven days off. Two things follow from that structure. Every work run is short — three or four shifts — and the cycle turns you from nights to days and back inside a single month, with as little as one day off in between.
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 9:00 AM on a rest day. A 3:00 PM wake puts the 12-hour night starting at 1800, which is the harder half of the cycle to hold. The 9:00 AM rest anchor is for the breaks. 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.
The four nights of the cycle. 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 |
Nights into days, or the last night into the break.
| 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 |
The three- and seven-day breaks.
| Wake anchor | 9:00 AM |
|---|---|
| Bright light | 9:00 AM to 10:30 AM |
| Caffeine | 10:00 AM to 10:30 AM (first cup), stop by 5:00 PM |
| Last real meal | by 8:30 PM |
| Wind-down | 11:30 PM to 12:00 AM |
| Sleep target | 1:00 AM |
Two features of the cycle do most of the damage, and both are structural. The first is the single day off between the three-day run and the three nights that follow it. One day is not enough time to move a body clock across twelve hours, so that turnaround is a night worked on a day schedule no matter what you do; the plan can only make it shorter, not painless. The engine gives it its own turnaround day-type for exactly that reason — a short deliberate sleep aligned to where you are going rather than a full sleep aligned to where you have been. The second is the seven days off at the end. That is long enough to fully return to daylight, which feels like a reward and means the four nights that open the next cycle start from zero.
The four-night run works like any night block: one time zone, sleep the days, do not flip mid-block. The turnaround out of nights is the dangerous part. Take a short, deliberate sleep after the last night rather than a full day sleep, get bright light after you wake from it, and go to bed early that evening. That is what moves you back in one day instead of three.
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 9:00 AM anchor gives a 1:00 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.
Turnaround 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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