Sleep Calculator

Written byOleh Soloninupdated 5 October 2026

Calculate

Wake-up or bedtime

Time to fall asleep, min

Result

Best option21:45 (6 cycles)
Option 223:15 (5 cycles)
Option 300:45 (4 cycles)
Short option: 3 cycles02:15 (3 cycles)

This result is informational only and is not professional advice.

Sleep in whole 90-minute cycles

Find a bedtime or wake-up time in whole 90-minute sleep cycles, allowing for the time it takes to fall asleep. It does not measure your sleep stages, so it cannot promise the alarm lands in light sleep.

Sleep runs in cycles of roughly 90 minutes, from light through deep sleep to REM. The idea here is to set the alarm at the boundary between cycles: waking from light sleep is easier than waking from deep sleep.

The calculation also allows for the time it takes you to fall asleep. Without that, an alarm set for 'six cycles' quietly takes fifteen minutes off your night.

How to use

Choose a mode: if you know when you must get up, the calculator suggests bedtimes; if you know when you go to bed, it suggests wake-up times.
Enter the time as HH:MM.
Enter how many minutes you usually take to fall asleep.
Pick the option with the number of cycles you want: six is nine hours of sleep, five is seven and a half.

When to go to bed to wake up on time

The calculator takes whole 90-minute cycles and your time to fall asleep off the wake-up time. To wake at 07:00 after five cycles, go to bed at 23:15; after six, at 21:45.

15 minutes to fall asleep. Every row comes from the calculator on this page.
Wake up	6 cycles (9 h)	5 cycles (7.5 h)	4 cycles (6 h)
06:00	20:45	22:15	23:45
06:30	21:15	22:45	00:15
07:00	21:45	23:15	00:45
07:30	22:15	23:45	01:15
08:00	22:45	00:15	01:45

When to get up after going to bed at 23:00

In the other direction the calculator adds the time to fall asleep and the cycles to your bedtime. If you take half an hour to drop off rather than fifteen minutes, every option moves fifteen minutes later.

Bed at 23:00, 15 minutes to fall asleep. Every row comes from the calculator on this page.
Cycles	Sleep, h	Wake up
6	9	08:15
5	7.5	06:45
4	6	05:15
3	4.5	03:45

What this calculator shows

Four bedtime or wake-up options, each a whole number of cycles
Options ordered from six cycles down to three
Your fall-asleep time built into the calculation

What to keep in mind

Assumes a 90-minute cycle, which is an average — real cycles run 70 to 120 minutes.
Total sleep matters more than cycle alignment. Five well-timed cycles do not beat eight hours if you need eight.

FAQs

What time should I go to bed to wake up at 7am?

At 21:45 for six cycles, 23:15 for five or 00:45 for four — if you take 15 minutes to fall asleep.

How much sleep does an adult need?

The American Academy of Sleep Medicine and the Sleep Research Society recommend at least 7 hours on a regular basis. Five cycles — 7.5 hours — meets that; four does not.

Do sleep cycles really last 90 minutes?

On average. Individual cycles range from about 70 to 120 minutes and change through the night, with deep sleep dominating early and REM later.

Which matters more: hitting a cycle or sleeping enough?

Sleeping enough. Cycle timing is a refinement that may make waking easier, not a way to need less sleep: five well-timed cycles do not replace eight hours if you need eight.

Why do I feel worse after a long lie-in?

If the alarm cuts into deep sleep, the grogginess lasts longer. A shifted weekend schedule also confuses your body clock — a consistent wake-up time helps more than extra hours on Saturday.

Does the snooze button help?

Snoozed minutes are broken, light sleep — not enough time for a full cycle. If you snooze every morning, it is more honest to set the alarm for the last press to begin with.

Worked example

A 07:00 alarm

Input: Wake at 07:00, 15 minutes to fall asleep

Output: Bed at about 21:45 for six cycles, or 23:15 for five

Note: Six cycles is nine hours of sleep, five is seven and a half — pick by how much sleep you actually need, then use the timing to fine-tune.

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