Sleep Calculator

The sleep calculator picks your bedtime and wake-up time based on sleep cycles. One cycle lasts about 90 minutes and falling asleep takes about 15 minutes on average. If you wake up between cycles rather than in the middle of one, there is no morning grogginess – even after a short night. Tell it when you need to wake up and it shows the best time to go to bed – or the other way around: when to go to bed to wake up refreshed.

How the calculation works

Sleep runs in cycles: how easy it is to wake depends on the phase you wake up in. Waking at the end of a cycle is easy – the body is almost awake already. Waking from deep sleep is hard: grogginess can last 1–2 hours. So it is easier to plan sleep in cycles than in hours: 4 cycles ≈ 6 hours, 5 cycles ≈ 7.5 hours, 6 cycles ≈ 9 hours. The calculator adds 15 minutes to fall asleep and offers full-cycle options.

How to use the calculator

Choose a mode. "I wake up at a set time" – enter your wake-up time and the calculator shows when to go to bed (6, 5, 4 or 3 cycles). "I go to bed" – enter your bedtime or tap "going to bed now" and the calculator shows wake-up options after 6, 5 and 4 cycles. Options with 5–6 cycles (7.5–9 hours) are highlighted as recommended – the adult sleep norm.

How much sleep do you need

For most adults the norm is 7–9 hours, which is 5–6 cycles. Regularly sleeping less than 6 hours reduces concentration and immunity; regularly more than 9 hours usually signals a weekly sleep debt or poor sleep quality. Individual variation exists: if you wake up refreshed after 6 hours, that is your norm. Judge by how you feel during the day and keep bed and wake times consistent at weekends – "catching up" on Saturday disrupts the rhythm as much as sleep loss.

How to fall asleep faster

15 minutes to fall asleep is an average; an alert brain takes longer. What helps: no screens (or night mode) 30–60 minutes before bed, a cool bedroom (18–20 °C), no caffeine after 3 p.m., a light dinner 2–3 hours before bed. If you are not asleep in 20 minutes, it is better to get up and read in dim light than to toss and turn – that way the brain does not associate the bed with being awake.

This calculation is for information only and is not medical advice. If you have persistent sleep problems, see a doctor.