Tell the calculator when you need to wake up, or when you are going to bed. It suggests times that fit whole 90-minute sleep cycles, so you are more likely to wake between cycles.
Results are estimates for planning. Check the figures before you make a financial or health decision.
How the Sleep calculator works
The tool counts back or forward in blocks of 90 minutes, which is the typical length of one sleep cycle. Cycles vary from person to person, so this is an approximation.
- If you know your wake time: it subtracts 6, 5, 4 or 3 cycles, plus the time you take to fall asleep, to give bedtimes.
- If you know your bedtime: it adds the time to fall asleep, then adds 3, 4, 5 or 6 cycles to give wake times.
Five cycles is 7 hours 30 minutes, marked as the best choice. Six cycles is 9 hours. The default allowance for falling asleep is 15 minutes, which you can change from 0 to 120.
Most adults need about 7 to 9 hours, so five or six cycles suits most people. Fewer than four cycles is shown for short nights but is not recommended regularly. The tool cannot allow for shift work, naps, illness or sleep disorders.
Tips and common mistakes
Pick a wake time you can keep every day, then count back. Set your alarm for the calculated time rather than a few minutes either side. Adjust the time to fall asleep if you usually take longer or shorter than 15 minutes. If you regularly feel tired after enough sleep, or have trouble sleeping, speak to a GP. This is a guide, not medical advice.
Frequently asked questions
How long is a sleep cycle?
About 90 minutes, though it varies between people and through the night. The calculator uses 90 minutes as a simple guide.
How much sleep do adults need?
About 7 to 9 hours for most adults, which is five or six cycles. Needs vary, so notice how you feel during the day.
Why does it add time to fall asleep?
You are not asleep the moment you get into bed. The allowance, 15 minutes by default, makes sure the cycles are counted from when you actually fall asleep.