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Sleep smarter.
Wake up refreshed.

Calculate the perfect bedtime or wake-up time based on your natural 90-minute sleep cycles. Plus: track sleep debt and plan the ideal nap.

When should I go to sleep?

Enter your wake-up time and we'll calculate the ideal bedtimes based on 90-minute sleep cycles. You need about 15 minutes to fall asleep — we've already factored that in.

What time should I set my alarm?

Going to bed now or at a set time? Enter when you'll fall asleep and we'll show you the best wake-up times to feel rested.

How much sleep do you owe yourself?

Enter how many hours you slept each night this week. Most adults need 8 hours. We'll calculate how much sleep debt you've accumulated.

Plan the perfect nap

Not all naps are equal. Waking mid-cycle leaves you groggy. Choose a nap length below, enter when you're starting, and we'll tell you exactly when to set your alarm.

20 min
Power nap
Stays in light sleep. Wake up alert and energized. Best for a quick afternoon boost.
90 min
Full cycle nap
Completes one full sleep cycle. Includes REM sleep. Wake up refreshed, not groggy.
Avoid
30–60 min nap
Wakes you mid-cycle. You'll likely feel worse than before. The "sleep hangover" zone.
Set your alarm for
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How sleep cycles work

Your brain cycles through five stages of sleep roughly every 90 minutes. Waking up between cycles — when your sleep is naturally lightest — leaves you feeling alert. Waking mid-cycle triggers "sleep inertia," that foggy, groggy feeling that can last for hours.

This calculator always suggests times that land at the end of a complete cycle, so your alarm wakes you at the lightest point in your sleep.

Why 90 minutes?

A full sleep cycle moves through: light sleep (stage 1 and 2), deep sleep (stage 3, also called slow-wave sleep), and REM sleep (rapid eye movement, where most dreaming happens). Each full cycle takes approximately 90 minutes, though this can vary slightly between individuals and across the night.

How many cycles do I need?

Most adults function best with 5–6 complete cycles per night (7.5–9 hours). Teenagers and younger adults often benefit from 6 or more. The "I only need 5 hours" camp is a very small percentage of the population — for most people, consistently short sleep accumulates as debt.

What is sleep debt?

Sleep debt is the cumulative shortfall between how much sleep you need and how much you actually get. Miss one hour of sleep for six nights and you've accumulated six hours of sleep debt. Research shows this impairs cognitive performance as significantly as pulling an all-nighter — even if you don't feel tired. The good news: sleep debt can be recovered, though it takes longer than a single weekend "catch-up."

The science of napping

A 20-minute nap keeps you in the lightest stages of sleep, so waking is easy and you feel immediately sharper. A 90-minute nap completes a full cycle, giving you REM sleep and leaving you genuinely restored. Anything between 30–60 minutes tends to end mid-cycle in deep sleep — waking from this stage triggers sleep inertia and leaves most people feeling worse than before the nap.

Frequently asked questions

What time should I go to sleep to wake up at 6am?
To wake at 6:00am feeling refreshed, aim to fall asleep at 10:45pm (5 cycles, 7.5 hrs), 9:15pm (6 cycles, 9 hrs), or 12:15am (4 cycles, 6 hrs) as a minimum. The calculator above factors in 15 minutes to fall asleep.
Is 6 hours of sleep enough?
For most adults, 6 hours (4 cycles) is consistently below the recommended amount and will accumulate sleep debt over time. A small percentage of people — sometimes called "short sleepers" — genuinely function well on 6 hours due to a genetic variant, but this is rare. If you feel fine on 6 hours, you may be one of them. If you need an alarm to wake up, you probably aren't.
How long does it take to recover from sleep debt?
Short-term sleep debt (a few days) can largely be recovered within a week or two of proper sleep. Chronic sleep debt (months or years of insufficient sleep) is more complicated — some cognitive effects may persist even after extended recovery sleep. The best approach is prevention: consistent 7.5–9 hour nights.
What is the best time to take a nap?
The ideal nap window for most people is between 1pm and 3pm, which aligns with a natural dip in the circadian rhythm. Napping later than 3–4pm can make it harder to fall asleep at your regular bedtime, disrupting your nightly sleep.
Why do I feel worse after a 45-minute nap?
A 45-minute nap typically ends in the middle of deep sleep (slow-wave sleep), the hardest stage to wake from. This causes sleep inertia — grogginess that can last 30–60 minutes. Stick to 20 minutes (before deep sleep begins) or 90 minutes (a full cycle) to avoid this.