Sleep calculator: when should I go to bed?

By Kevin Buhl Jakobsen · Everything is worked out in your browser; nothing is saved or sent · Updated 7. Nov 2026

How the calculator works

Sleep isn't the same all night. We move through cycles of light sleep, deep sleep and dream sleep (REM), and in adults one cycle usually lasts around 90 minutes, though it can vary from roughly 70 to 120. Waking is easiest at the end of a cycle, when sleep is light. If the alarm drags you out of deep sleep, you get the heavy, foggy feeling researchers call sleep inertia.

So the calculator adds up whole 90-minute cycles and allows 15 minutes to fall asleep, which is typical for healthy adults. For a nap, it allows 10 minutes to drift off.

Five or six cycles (7½ or 9 hours) are marked as recommended, because the sleep experts at the US National Sleep Foundation recommend 7–9 hours for adults. Four cycles (6 hours) beats waking mid-cycle, but is too little as a habit.

What it can't do

Your own cycle might be a little shorter or longer than 90 minutes, and it changes over the night: deep sleep comes mostly early on, dream sleep mostly towards morning. Use the times as a good starting point, and adjust by 10–15 minutes if you still wake up groggy. If you can't fall asleep, staring at the clock won't help: read our article on what helps when you're awake at 3 a.m.

About naps: 10–20 minutes gives the most fresh energy with the least fog afterwards. Around 90 minutes gives a full cycle, for example before a night shift. Between 30 and 60 minutes is when you're most likely to wake from deep sleep. Read more in our guide to power naps.

General information, not medical advice. If you're tired all the time despite enough sleep, talk to a doctor.