Sleep Time Calculator
Enter a wake-up or bedtime to get optimal sleep recommendations based on 90-minute sleep cycles.
Sleep Cycle Guide
Sleep consists of roughly 90-minute cycles. Waking at the end of a cycle helps you feel more refreshed. Adults are recommended 7–9 hours (5–6 cycles).
Worked Examples
To wake at 07:00 after five cycles you should fall asleep around 23:30, allowing 15 minutes to nod off.
Sleeping at 01:00 with six cycles ends around 08:45, which is why the same duration can feel very different depending on where it stops.
What the Cycle Model Assumes
Cycles average 90 minutes but vary between 70 and 120 minutes per person and per night, and the first cycles carry more deep sleep. The tool assumes 15 minutes to fall asleep and does not account for sleep apnoea, shift work, caffeine or alcohol, which change both duration and quality.
Frequently Asked Questions
- How many cycles do I need?
- Most adults need five to six cycles, roughly 7.5 to 9 hours. Teenagers need eight to ten hours and young children considerably more.
- Why do I wake up tired after eight hours?
- Waking in the middle of deep sleep causes sleep inertia. Timing the alarm to the end of a cycle usually feels lighter even with slightly less total sleep.
- Does the calculator replace a sleep study?
- No. Loud snoring, gasping, daytime sleepiness or insomnia lasting more than a month need medical assessment, not a schedule.