The standard advice to shift workers is to cut down on caffeine. Expert consensus says close to the opposite: used deliberately, it is one of the few countermeasures that reliably works on a night shift. What matters is when, not whether.
WHAT THIS PAGE WILL NOT TELL YOU
This page explains how the timing works and why. It does not print your six times, because they are not printable: they move with your finish time, your commute and the hour you wake with no alarm. Four questions, about forty seconds, no account.
- Your crash window
- Bright light: start and stop
- Sunglasses on: start and stop
- Main sleep: in bed and up
- Pre-shift nap: and when to set the alarm
- Last caffeine
FREE TO SEE YOUR CRASH WINDOW · NO ACCOUNT · 40 SECONDS
The half-life is the whole calculation
Caffeine has a half-life of about five hours. So half of a 5am coffee is still in you at 10am, when you are trying to sleep. That is why the cutoff is not a fixed time of day. You set it backwards from when you actually go to bed, and your bedtime is not a day worker's.
Everything below is the mechanism. The six clock times it produces depend on your finish time, your commute and how early you wake unaided, so this page cannot print them. Get yours in about forty seconds.
The first dose is worth more than the last
Caffeine early in a shift buys alertness while you can still use it. Caffeine at the end is borrowed against sleep you will not get. It also arrives when your worst hour is already dragging you down anyway. If you are reaching for a coffee in the last hours, the real fix is usually the sleep before the shift, or a nap. Not the cup.
Working out your own cutoff
Take the time you intend to be asleep and work back about six hours. That is your last dose. The result surprises most people, because on a night roster it usually lands in the middle of the shift rather than near the end of it. Working it out needs your finish time and your commute, since those two are what decide when you are actually asleep, and they are the pair the tool starts from.
What it cannot do
Caffeine masks sleepiness, it does not replace sleep, and it does nothing to move your body clock. The timing that actually shifts your clock is light, and no amount of coffee substitutes for getting that part right. Use it as a countermeasure inside a plan, not as the plan.
Common questions
+ − When should I stop drinking coffee on a night shift?
About six hours before you plan to be asleep. Caffeine has a half life of roughly five hours, so half of a 2am coffee is still in you at 7am. If you sleep at 8am, the last dose wants to land near 2am, not at 5am when the last stretch of the shift is hardest.
+ − Should shift workers avoid caffeine?
No, and the standard advice to avoid it is one of the things expert consensus specifically rejects for shift workers. Caffeine used deliberately before and during the shift is a countermeasure. The problem is not caffeine, it is caffeine at 5am.
+ − Is coffee at the start or the end of the shift better?
The start. A dose early in the shift is working during the hours you need it and is mostly cleared by the time you sleep. A dose at the end arrives after your worst hour has already passed and is still in your system when you get into bed.
+ − Can caffeine replace sleep?
No. It masks how tired you are without fixing it, which is a specific hazard on a night shift because the thing it hides is the thing telling you to stop. Use it to hold a line you planned for, not to extend past one.
+ − What is the 10 5 3 2 1 rule for sleep?
A wind-down countdown, usually written 10-3-2-1-0: no caffeine ten hours before bed, no heavy food or alcohol three hours before, no work two hours before, no screens one hour before, and no hitting snooze. Nothing in it is wrong. The problem for a shift worker is that every number counts backwards from bedtime, and bedtime is the thing you do not know. A day worker can assume eleven at night. You cannot. Work out your sleep window first and the countdown has something to count back from. The caffeine number is also the weakest one: ten hours is a blunt default, and a half life of about five hours puts the useful cutoff nearer six hours before you sleep.
What this is based on
Every rule the plan runs on, and where each one comes fromRelated
ShiftDawn is a scheduling and education tool built on published circadian research. Not medical advice, not a diagnosis. If you suspect a sleep disorder, see a clinician.