Tell us when you woke up and what you have had to drink. We will tell you if a nap is a good idea, and whether there is still time for coffee.
Your day
How fast do you clear caffeine?
What I have had todayNew drinks are added at the time set above.
The verdict
The alarm leaves about 10 minutes to drop off.
Caffeine in you now
Left at bedtime
Last coffee by
Caffeine in your body today
Estimate. Green band is the easiest nap window.
Coffee nap
Tonight
How it works
Caffeine fades slowly
The half-life averages about 5 hours but varies a lot between people. Half of a 3 pm coffee is still with you at 8 pm, which is why the curve above matters.
Nap early, nap short
The easiest window is the early-afternoon dip, roughly 6 to 8 hours after you wake. Short naps lower the risk of grogginess, so we aim for about 20 minutes, with a full 90 as the long option.
The coffee nap
Caffeine is mostly absorbed within about 45 minutes. In one small study, coffee followed straight away by a nap of under 15 minutes beat coffee alone for staying alert.
The science, and what we made up
The caffeine curve and the nap basics rest on research. The exact cutoffs are our own rules of thumb, and we say which is which.
Backed by research
Caffeine has a half-life of about 5 hours, and it varies a lot. An Institute of Medicine report gives a mean of about 5 hours with a range of 1.5 to 9.5, shifted by pregnancy, obesity, the pill, smoking and altitude. It also says 99% is absorbed within 45 minutes. Source
Late caffeine costs sleep. In a small study of 12 healthy sleepers, 400 mg of caffeine six hours before bed cut measured sleep by more than an hour. Drake et al., 2013
A coffee nap can beat coffee alone. In a driving simulator, 12 sleepy adults had far fewer incidents after 200 mg of caffeine plus a nap of under 15 minutes (9% of the placebo level) than after caffeine alone (34%). Reyner and Horne, 1997
A planned short nap helps. On long-haul flights, crew given a 40-minute rest opportunity slept about 26 minutes on average and showed better alertness and performance than crew who did not. NASA, Rosekind et al.
Two things make you sleepy. Sleep pressure builds the longer you are awake, and the body clock lowers alertness in the early afternoon. Borbély, two-process model
Our rules of thumb
The 50 mg bedtime line. The sleep study above used 400 mg, so it does not tell us where a safe level is. We picked 50 mg as a simple cutoff.
The nap window of 6 to 8.5 hours after waking. It approximates the early-afternoon dip, which follows your body clock more than your wake time.
“Not yet” under 4.5 hours awake, “Not now” with under 6 hours to bedtime. Reasonable guesses, not research cutoffs.
20-minute and 90-minute naps. Short naps are widely advised, but a 2017 review found the evidence that they avoid grogginess is mixed and depends on time of day and prior sleep. Hilditch et al.
Drink strengths and the absorption curve. Typical values and a simple curve. Real cups and real bodies vary.
Estimates for planning, not medical advice. If you have a heart condition, are pregnant, or take medication, ask your doctor about caffeine.