What time should I go to bed to feel rested?

Choose your wake time — the calculator suggests bedtimes in whole 90-minute cycles (usually 6, 7.5 or 9 hours of sleep) plus time to fall asleep. Waking at the end of a cycle feels easier than mid-cycle.

What is a sleep cycle?

A period of about 90 minutes through light and deep stages and REM. There are usually 4–6 a night. Waking at the end of a cycle feels easier than during deep sleep.

How many hours should I sleep?

Adults 7–9 hours, teens 8–10, older adults 7–8, children more. The calculator shows the norm for your age and marks the optimal options (5–6 cycles).

Why don’t I feel rested after 8 hours?

It could be the waking stage (you woke in deep sleep), an irregular schedule, sleep quality (apnea, screens, caffeine) or your individual cycle length. If it’s persistent, it’s worth checking the causes.

Is the cycle calculation accurate?

It’s a guide: cycle length varies (80–100 minutes). A regular schedule and enough total sleep matter more than a to-the-minute calculation.

Sleep calculator: when to go to bed or wake up

Choose what to calculate — when to go to bed to wake at a set time, or when to wake up if you go to bed now. The calculator suggests times based on ~90-minute sleep cycles plus time to fall asleep. Enter your age to see the recommended sleep duration.

Calculate sleep times by cycles

Enter a time (or age) — the result appears instantly.

Recommended sleep by age (NSF)

Recommended daily sleep duration per the National Sleep Foundation.

Age	Sleep
1–2 years	11–14 hours
3–5 years	10–13 hours
6–13 years	9–11 hours
14–17 years	8–10 hours
18–64 years	7–9 hours
65+ years	7–8 hours

How sleep cycles work

Sleep runs in cycles of about 90 minutes: each cycle takes you through light and deep stages and REM sleep. It’s easier to wake at the end of a cycle, in a light stage, than mid-deep-sleep — so you feel fresher even after less sleep.

That’s why the calculator suggests times that are whole cycles: 4, 5 or 6 cycles — roughly 6, 7.5 and 9 hours of sleep. About 15 minutes to fall asleep is added.

How much to sleep

Adults usually need 7–9 hours, teens more, older adults a little less. 5–6 full cycles (7.5–9 hours) are optimal — the calculator marks those options. Regular sleep loss raises the risk of metabolic, blood-pressure and mood problems.

Cycle length varies a little between people (80–100 minutes), so the calculation is a guide. Going to bed and waking at roughly the same time each day matters more than the exact minute.

Frequently asked questions

Choose your wake time — the calculator suggests bedtimes in whole 90-minute cycles (usually 6, 7.5 or 9 hours of sleep) plus time to fall asleep. Waking at the end of a cycle feels easier than mid-cycle.
A period of about 90 minutes through light and deep stages and REM. There are usually 4–6 a night. Waking at the end of a cycle feels easier than during deep sleep.
Adults 7–9 hours, teens 8–10, older adults 7–8, children more. The calculator shows the norm for your age and marks the optimal options (5–6 cycles).
It could be the waking stage (you woke in deep sleep), an irregular schedule, sleep quality (apnea, screens, caffeine) or your individual cycle length. If it’s persistent, it’s worth checking the causes.
It’s a guide: cycle length varies (80–100 minutes). A regular schedule and enough total sleep matter more than a to-the-minute calculation.

Poor sleep? The cause may be in your labs

Upload your tests — AI checks iron, vitamin D, thyroid hormones and other values that affect sleep.

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This calculator is for reference and information only. For persistent insomnia, snoring or daytime sleepiness, see a doctor — sleep disorders are possible.