Sleepytime

A rough sleep cycle calculator. Real cycles vary between 70 and 120 minutes (between people and across a single night), so treat these as gentle suggestions, not commandments. The single strongest rule is just to get seven to nine hours total.

NOTES

⋆ Most adults feel best on five full cycles (~7.5h), highlighted above. Four cycles (~6h) is the floor; less than that is sleep debt you'll repay later.
⋆ To find your real cycle length: on a free weekend, sleep until you wake naturally and divide hours slept by five. Most people land between 80 and 100 minutes.
⋆ Caffeine has a half-life of around five hours. A 2pm coffee is still a quarter-strength at midnight. Eight hours before bed is a safe-ish cutoff.
⋆ Cycles lengthen through the night. The first is often only ~80 minutes, the last closer to 100. Most of your dreaming happens in the final cycle.