Work out bedtimes and wake times in complete 90-minute sleep cycles, with an adjustable allowance for the time taken to fall asleep. Runs entirely in your browser — your numbers never leave this device.
| Cycles | Sleep time | Wake up |
|---|---|---|
| 3 | 4.5 h | 03:45 |
| 4 | 6 h | 05:15 |
| 5 | 7.5 h | 06:45 |
| 6 | 9 h | 08:15 |
The calculation counts sleep in 90-minute cycles. 90 minutes is an average — individual sleep cycles vary in length.
Informational only. This calculator applies a published formula to the numbers you enter — it is not medical advice, a diagnosis, or a substitute for a clinician. Talk to a qualified professional about decisions concerning your health.
| Cycles | Total sleep |
|---|---|
| 3 | 4.5 hours |
| 4 | 6 hours |
| 5 | 7.5 hours |
| 6 | 9 hours |
This calculator is built on the 90-minute sleep-cycle model: sleep is counted in complete cycles of 90 minutes, and a wake time is placed at a cycle boundary rather than mid-cycle. Counting forward from a bedtime adds the latency — the time taken to fall asleep, set at 15 minutes by default and adjustable — then whole multiples of 90 minutes. Counting backward from a required wake time subtracts the same two quantities. Both directions are the same arithmetic with the sign reversed.
The cycle table states what each count means in total sleep: 3 cycles is 4.5 hours, 4 is 6 hours, 5 is 7.5 hours and 6 is 9 hours, before latency is added to the time in bed. The worked examples list times for several cycle counts at once, because the practical question the model answers is comparative — which cycle boundary falls at a workable clock time.
The 90-minute figure is the model's standard average cycle length; individual cycles vary in length across a night and between people, so the times are the model's arithmetic, presented for information and planning. Latency is an input precisely because time to fall asleep varies, and changing it shifts every suggested time by the same amount.
90 minutes is the standard average cycle length used by the sleep-cycle model this calculator implements. Individual cycles vary, so the model gives boundary times based on the average, and the table shows the total sleep each cycle count represents.
The allowance for time taken to fall asleep, added between getting into bed and the first cycle starting. It defaults to 15 minutes and can be changed; every result shifts by exactly the change made.
No, and the page keeps them separate: the cycle table counts sleep only, while the clock times include latency. In bed at 23:00 with 15 minutes latency and 5 cycles means 7.5 hours of sleep ending at 06:45, after 7 hours 45 minutes in bed.
No. The page applies the 90-minute cycle model to clock times for information and planning. It does not assess sleep or advise any person; persistent sleep concerns belong with a clinician.
No. The calculation runs entirely in the browser and nothing entered is uploaded, stored or tracked.
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