Wake-Up Time Calculator

Free, no signup, runs in your browser.

Why this matters: waking from deep sleep generally brings the worst grogginess (sleep inertia). Waking near the end of a cycle makes it more likely you surface from lighter sleep, which tends to feel easier. Cycles vary, so treat the times as a guide. This tool computes both directions: when to sleep if you must wake at X, and when to wake if you sleep now.

If I must wake at...

Desired wake-up time

Go to bed at one of these times

Each option adds a 14-minute buffer to fall asleep, then full 90-minute cycles.

If I sleep now, when should I wake up?

How the calculator works

A complete sleep cycle averages 90 minutes and runs through light sleep, deep sleep, and REM. Waking at the end of a cycle (when you are back in light sleep) tends to feel easiest. Waking from deep sleep generally brings the most sleep inertia, although not every study finds this.

Healthy adults usually take 10 to 20 minutes to fall asleep, so the calculator adds a 14-minute buffer to your bedtime before counting cycles. The numbers are averages, not promises. Real cycles vary, roughly between 70 and 120 minutes, depending on the person, the night and how far into the night you are.

How many cycles do you actually need?

6 cycles (9 hours). Teenagers, athletes in heavy training, anyone recovering from sleep debt.
5 cycles (7.5 hours). The sweet spot for most adults, within the 7 hours or more recommended by the American Academy of Sleep Medicine.
4 cycles (6 hours). Below the 7 hours recommended for adults. Fine for an occasional night, not as a habit.
3 cycles (4.5 hours). Emergency mode. Expect impaired cognition the next day even if you wake cleanly.

Why an alarm matters more than the calculator

Computing the perfect bedtime does not matter if your alarm lets you snooze past the time you targeted. Each snooze trades a clean wake-up at the end of a cycle for lighter, broken sleep and a later start. That is the exact pattern snoozing creates.

ByeBed has no snooze button: its alarms are system alarms created with iOS AlarmKit, and if you stop one without finishing your mission, it rings again, up to 10 times over 15 minutes. That makes it much harder to snooze half an hour past the time the calculator gave you.