Sleep Calculator
Find the best times to go to sleep or wake up based on 90-minute sleep cycles. Waking between cycles leaves you feeling refreshed instead of groggy.
How to use
- Choose whether you want to calculate bedtime (given a wake time) or wake time (given a bedtime).
- Enter your target wake time or bedtime and select your age group.
- Click Calculate to see 3 optimal times based on 4, 5 and 6 complete sleep cycles.
Frequently asked questions
What is a sleep cycle?
A sleep cycle lasts about 90 minutes and includes light sleep, deep sleep and REM (dream) sleep. Most adults need 4–6 complete cycles (6–9 hours) per night. Waking at the end of a cycle feels more natural than waking mid-cycle.
Why does the calculator add 15 minutes?
The 15-minute buffer accounts for the average time it takes to fall asleep after lying down. If you fall asleep faster or slower, adjust the time accordingly.
How many hours of sleep do I need?
Adults need 7–9 hours (4–6 cycles). Teenagers need 8–10 hours. Children need more. The calculator shows options for 4, 5 and 6 cycles so you can choose based on your schedule.
Does napping count?
Short naps (20–30 minutes) improve alertness without entering deep sleep. A full 90-minute nap completes one cycle and can partially compensate for lost nighttime sleep.