Sleep Calculator

A bedtime or wake-up time — aligned to full 90-minute sleep cycles.

Based on 90-minute sleep cycles plus about 15 minutes to fall asleep — waking up at the end of a cycle (rather than mid-cycle) tends to feel less groggy.

Try waking up at
3:45 AM
3 cycles (~4.5h)
5:15 AM
4 cycles (~6.0h)
6:45 AM
5 cycles (~7.5h)
8:15 AM
6 cycles (~9.0h)

5-6 cycles (7.5-9 hours) covers the commonly recommended range for adults — individual sleep needs do vary, though.

Frequently asked questions

Why do sleep cycles matter for when I wake up?

Sleep moves through repeating stages roughly every 90 minutes, including lighter and deeper phases. Waking up during a deep stage tends to feel groggy and disorienting, while waking near the end of a cycle (in a lighter stage) generally feels easier.

Why does the calculator add 15 minutes before the first cycle?

It accounts for the typical time it takes to actually fall asleep after getting into bed — without that buffer, the cycle timing would assume you fall asleep instantly, which isn't realistic for most people.

Is 90 minutes exact for everyone?

No — it's a commonly cited average, but individual cycle length varies somewhat from person to person and night to night. Treat the suggested times as a useful starting point rather than an exact science.

This is a general wellness tool, not medical advice — if you're experiencing ongoing sleep difficulties, consider speaking with a healthcare provider.