Why does the calculator use 90-minute cycles?

Sleep happens in 90-minute cycles consisting of REM and non-REM stages. Waking up at the end of a cycle helps improve energy and alertness.

How many sleep cycles do I need?

Most adults need between 4 and 6 sleep cycles, equal to roughly 6 to 9 hours of sleep.

Does this tool store my information?

No. All calculations happen locally in your browser without storing or sending any personal data.

Sleep Calculator

Calculate the best time to sleep or wake up based on healthy 90-minute sleep cycles.

Enter wake-up time or bedtime (choose only one)

I want to wake up at:

I want to sleep at:

How This Sleep Calculator Works

Healthy sleep happens in 90-minute cycles. Waking up at the end of a cycle makes you feel refreshed, while waking up in the middle of a cycle can cause tiredness or grogginess. This calculator recommends the best times to sleep or wake up based on these cycles.

When you choose a wake-up time, the tool calculates backwards in 90-minute cycles to find ideal sleep times. If you choose a bedtime, it calculates forward to find the best wake-up times. All calculations happen instantly in your browser.

This tool does not save any data and works completely offline in your device for fast and private results.

Frequently Asked Questions

Why 90-minute sleep cycles?

Your brain moves through stages of light sleep, deep sleep, and REM sleep. Each full cycle takes about 90 minutes. Waking up at the end of a cycle helps you feel more energetic.

How many cycles should I sleep?

Most adults feel best with 4 to 6 sleep cycles, equal to 6 to 9 hours of sleep.

Does this replace medical advice?

No. This is a general lifestyle tool, not a medical diagnosis. Sleep needs vary for each person.

Is my data saved?

No. Your inputs never leave your browser. Nothing is stored or shared.