Wake-Up Time Calculator

Free, no signup, runs in your browser.

Why this matters: waking in the middle of a deep-sleep stage causes the worst grogginess (sleep inertia). Waking at the end of a 90-minute cycle leaves you in light sleep, which is far easier to leave. 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 accounts for a 14-minute average time to fall asleep, then adds 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) is when you feel most rested. Waking mid-deep-sleep is when sleep inertia is at its worst.

Average sleep onset for healthy adults is about 14 minutes, so the calculator adds that buffer to your bedtime before counting cycles. The numbers are averages, not promises. Real cycles drift between 80 and 110 minutes depending on the person and the night.

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. Backed by the bulk of sleep research.
4 cycles (6 hours). The lower bound for short-term function. Sustainable for a few nights, not long term.
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 through the cycle you targeted. Snoozing back into deep sleep, then jolting yourself awake 15 minutes later, gives you the worst of both worlds (incomplete cycle plus deep sleep wake-up). That is the exact pattern snoozing creates.

ByeBed removes the snooze button at the system level using iOS AlarmKit. You wake when the calculator says you should, not 30 minutes later.