Sleep Calculator

Works out when to go to bed for a chosen wake-up time, or when to wake up if you go to bed now or at a set time, counting in whole sleep cycles. Use it to decide what time to go to sleep.

How to use

1. Under "Calculate", choose "Bedtime for a wake-up time" or "Wake-up time for a bedtime".
2. Enter the "Wake-up time" or the "Time you go to bed". To start now, tick "I am going to bed now".
3. If needed, change "Time to fall asleep" and "Sleep cycle length" to suit you.
4. Read the time cards for 4 to 6 sleep cycles, each with the total sleep and the time in bed.

How it works

• Bedtime = wake-up time − time to fall asleep − number of cycles × cycle length. The defaults are 15 minutes to fall asleep and 90-minute cycles; the cycle can be set from 80 to 110 minutes.
• Cycle length and the time it takes to fall asleep are averages that differ between people and from night to night. Use the result as a guide only, and see a doctor if sleep problems continue.
• Open "Recommended sleep by age" to see the National Sleep Foundation's 2015 recommendations.

Questions and answers

What time should I go to bed to wake up at 7 am?

With the default settings, go to bed at 9:45 pm (6 cycles), 11:15 pm (5 cycles) or 12:45 am (4 cycles).

If I go to bed at 11 pm, when should I wake up?

With the default settings, at 5:15 am, 6:45 am or 8:15 am. These are the ends of 4, 5 and 6 sleep cycles.

Why does it count in 90-minute steps?

One sleep cycle lasts about 90 minutes on average, which is the common textbook figure. Cycles differ between people, so the length can be changed between 80 and 110 minutes.

How many hours of sleep does an adult need?

The National Sleep Foundation table on the page gives 7–9 hours for ages 18–64, 7–8 hours for 65 and older, and 8–10 hours for ages 14–17.