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Sleep Cycle Calculator

Find a wake-up time that lands you at the end of a full 90-minute sleep cycle.

Inputs

5-6 cycles (7.5-9 hours) is typical for adults.

Saved Scenarios

— select 2+ to compare

Wake-Up Hour (24h)

6

Wake-Up Minute

45

Total Sleep (hours)

7.5

Spark says

How it's calculated

Formula

Wake Time=(Bedtime+Cycles×90 min+15 min) mod 24hWake\ Time = (Bedtime + Cycles \times 90\ min + 15\ min) \bmod 24h
90\ min
— Approximate length of one full sleep cycle
15\ min
— Typical time to fall asleep

What is the Sleep Cycle Calculator?

Sleep occurs in cycles of roughly 90 minutes each — waking up at the end of a complete cycle (rather than mid-cycle) is widely reported to feel less groggy than waking in the middle of deep sleep.

How to use it

  1. 1 Enter your bedtime.
  2. 2 Choose how many sleep cycles you want (5-6 is typical for adults).

Worked examples

Bedtime 23:00, 5 cycles

Wake up around 6:45 (24h), after 7.5 hours of sleep.

Try it

Limitations

  • •90 minutes is an average — actual cycle length varies by person and by night (roughly 70-120 minutes), so treat this as a helpful estimate rather than a precise prediction. Minutes are displayed without a leading zero (e.g. '5' rather than '05').

Frequently asked questions

Why 15 minutes to fall asleep?

This is a commonly used average sleep-onset time — if you know you typically fall asleep faster or slower, adjust your target bedtime accordingly.