How much sleep do adults actually need?

Most adults need 7 to 9 hours per night, equivalent to about 5 to 6 full sleep cycles.

Why does waking mid-cycle feel worse?

Waking during deep sleep can cause grogginess known as sleep inertia, while waking at a cycle boundary generally feels smoother.

Is this a substitute for treating a sleep disorder?

No, this tool is for general sleep timing guidance only. Consult a doctor for persistent sleep issues.

Sleep Calculator

Find the best bedtime or wake-up time based on sleep cycles

Wake-up Time

What is the Sleep Calculator?

The Sleep Calculator works out the best time to go to bed or wake up based on natural 90-minute sleep cycles. Waking up at the end of a full cycle — rather than in the middle of one — tends to leave you feeling more refreshed, even with the same total amount of sleep.

How to Use the Sleep Calculator

Choose a mode — "I want to wake up at..." or "I want to sleep at...".
Enter your target time.
Pick a result from the list of times, each showing a whole number of 90-minute sleep cycles.

Why Sleep Cycles Matter

A full sleep cycle lasts about 90 minutes and moves through light sleep, deep sleep and REM sleep. Most adults complete 5-6 cycles per night (7.5–9 hours). This calculator adds roughly 15 minutes to account for the time it typically takes to fall asleep.

Frequently Asked Questions

Most adults need 7-9 hours per night, equivalent to about 5-6 full sleep cycles. Individual needs vary, so use this as a general guide rather than a fixed rule.

Waking during deep sleep (part of the middle of a cycle) can cause grogginess known as sleep inertia. Waking at the boundary between cycles, when sleep is lighter, generally feels smoother.

No. This tool is for general sleep timing guidance only. If you have ongoing trouble sleeping, persistent fatigue, or suspect a sleep disorder, speak with a doctor.