How long is a sleep cycle?

A full sleep cycle takes about 90 minutes on average and includes light sleep, deep sleep, and REM sleep. Most adults go through 4-6 cycles per night. Waking at the end of a cycle (rather than in the middle) is what makes you feel refreshed.

How many hours of sleep do I need?

Most adults need 7-9 hours per night. Teenagers need 8-10, school-age children 9-12, and adults over 65 often need 7-8. The exact need varies by individual; some function well on 6.5, others need 9.

What time should I go to bed?

Work backward from your wake time in 90-minute increments. If you need to wake at 7am and fall asleep in 15 minutes, going to bed at 9:45pm gives you 6 full cycles (9 hours). Our calculator accounts for sleep onset time automatically.

How accurate is the 90-minute sleep cycle theory?

The 90-minute cycle is an average; actual cycles vary from 70-120 minutes and shift throughout the night. The first half of the night has more deep sleep, the second half more REM. Despite variations, the 90-minute rule is useful for planning bedtimes.

Sleep Calculator - Optimal Sleep Cycles

Choose a wake time or bedtime

Type your desired wake time (e.g. 7 AM) or bedtime (e.g. 11 PM). The calculator will suggest the optimal other end of your sleep window.

We apply 90-minute sleep cycles

A full sleep cycle is about 90 minutes, moving through light, deep, and REM sleep. Waking between cycles feels more refreshed than waking mid-cycle.

Pick your cycle count

Choose 4, 5, or 6 cycles (6h, 7.5h, 9h). We suggest wake times that align with cycle ends and add 15 minutes for falling asleep.

Key things to know about our sleep calculator:

Most adults need: 7-9 hours of sleep per night. The 7.5h and 9h options are usually best for full rest. The 6h option is the minimum for one night.
Sleep cycles vary: First cycles have more deep sleep, later cycles have more REM. Personal variation is normal; the calculator is a starting point, not a strict rule.
Pair with consistency: Going to bed and waking at the same time every day, even weekends, leads to better long-term sleep than varying bedtimes.

For related calculations, try our time calculator.

Frequently asked questions

Everything you need to know about this calculator. Can't find what you're looking for? Email our team.

A sleep calculator is a free tool that finds the best bedtime or wake time based on 90-minute sleep cycles. Our sleep calculator works backward from a desired wake time, or forward from a chosen bedtime, to suggest 4, 5, or 6 cycle options. The sleep calculator helps you wake up between cycles for better rest and easier mornings.

How to find the best bedtime or wake time

Our sleep calculator lets you use 90-minute sleep cycles to plan a bedtime or wake time that leaves you refreshed, in three steps.

1
Pick the direction
Choose 'I want to fall asleep at X' or 'I need to wake up at X'. The calculator works the math backward or forward from your target time.
2
Enter your target time
Type the time you want to fall asleep or wake up. The calculator adds or subtracts 15 minutes for average sleep onset time automatically.
3
Read the result
The result lists 4-6 suggested times based on full sleep cycles. Each option is 90 minutes apart, and waking at the end of a cycle is what makes you feel most refreshed.

Sleep Calculator

title

How our sleep calculator works

Choose a wake time or bedtime

We apply 90-minute sleep cycles

Pick your cycle count

Key things to know about our sleep calculator:

Verified accuracy

Instant results

Your data stays private

Learn as you calculate

Frequently asked questions

How to find the best bedtime or wake time

Pick the direction

Enter your target time

Read the result

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