Sleep Calculator
Choose when you need to wake up — or when you are going to bed — and get times that fit whole sleep cycles, so you are more likely to wake refreshed.
Result
Choose when you want to wake up or go to sleep.
How to use this calculator
- Choose “Wake up at” or “Go to bed at” and enter the time.
- Adjust how long you take to fall asleep and your cycle length.
Formula
Bedtime = wake time − (cycles × cycle length) − time to fall asleep. Options for 6, 5, 4 and 3 cycles are shown.
Worked example
Waking at 7:00
With 15 minutes to fall asleep, go to bed at 21:45 for 6 cycles (9 hours) or 23:15 for 5 cycles (7.5 hours).
Assumptions and limitations
- Everything runs in your browser; nothing you enter is uploaded or stored.
- Cycle lengths vary between people and through the night; 90 minutes is an average.
Frequently asked questions
How much sleep do adults need?
Most adults need 7–9 hours — about 5 to 6 cycles.
Why do I feel groggy after a long sleep?
Waking during deep sleep causes sleep inertia. Waking at the end of a cycle can help.