Sleep calculator

Sleep calculator

How it works

1. 01

   A night is made of 4 to 6 cycles of about 90 minutes, each going from light sleep to deep sleep and dreams. Waking up during deep sleep leaves you groggy; waking up at the end of a cycle feels much easier.

2. 02

   Adults generally need 5 to 6 cycles, about 7 h 30 to 9 h. Cycles vary from one person to another: adjust by 10 to 15 minutes if you need to.

These tools give general information. They do not replace the advice of a doctor or a qualified professional.

Frequently asked questions

Why 90-minute cycles?

A sleep cycle moves from light to deep sleep and then to REM (dream) sleep in about 90 minutes, with variations of 70 to 120 minutes between people. Waking at the end of a cycle, in light sleep, is easier than in the middle of deep sleep.

Is a 6-hour night enough?

Rarely for an adult: 7 to 9 hours is the recommended range. Below that, attention, mood and immunity decline, even if you do not feel tired. Four cycles (6 h) is a floor for an occasional short night, not a routine.

I wake up at the right time but still feel groggy.

Sleep inertia can last 15 to 30 minutes even after a full night. Light, water and a little movement shorten it. If it persists every day, check the quality of your sleep (snoring, breaks, screens before bed).

How long should a nap be?

Either 10 to 20 minutes (no deep sleep, quick refresh) or a full 90-minute cycle. In between, you wake in deep sleep and feel worse. Before 3 pm, so as not to disturb the night.

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