Calculate the perfect bedtime using your natural 90-minute sleep cycles. Trusted by over 50,000 people worldwide.
Calculate My Sleep โThe science of 90-minute sleep cycles explained
Tell us when you need to be awake โ for work, school, or your morning routine.
Sleep occurs in 90-minute cycles. Waking in the middle of a cycle causes grogginess. We find exact safe windows.
Go to bed at the right time and your body surfaces from light sleep โ feeling refreshed without an alarm jolt.
Based on research by Dr. Matthew Walker (Why We Sleep, 2017) and the National Sleep Foundation guidelines.
Based on 90-minute cycles + 15 minutes to fall asleep
A complete sleep cycle lasts approximately 90 minutes and moves through 4 stages: N1 (light sleep), N2 (deeper light sleep), N3 (deep/slow-wave sleep), and REM (rapid eye movement). Waking up at the end of a cycle โ during the lightest stage โ is when you feel most naturally alert. Interrupting deep sleep or REM causes the foggy, groggy feeling known as sleep inertia.
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Find out how much sleep you're actually missing this week
Sleep debt is the cumulative difference between the sleep your body needs and the sleep you actually get. Unlike financial debt, you can't fully "pay it back" all at once โ chronic sleep deprivation has lasting effects on cognition, mood, and immune function. The best recovery strategy is to gradually increase your sleep time by 30โ60 minutes per night over 1โ2 weeks while maintaining a consistent wake time.
Backed by sleep science research
Blue light (400โ490 nm wavelength) from phones and laptops suppresses melatonin production by up to 50%, delaying the onset of sleep by up to 3 hours.
Your core body temperature needs to drop 1โ2ยฐF to initiate sleep. The ideal bedroom temperature is 65โ68ยฐF (18โ20ยฐC). A cooler room accelerates this process.
A consistent wake time โ even on weekends โ is the single most powerful anchor for your circadian rhythm. It stabilizes sleep pressure and makes falling asleep easier.
A coffee at 3 PM still has half its caffeine in your system at 10 PM. For good sleep, most adults should cut off caffeine intake by 2 PM, or 3 PM at the latest.
A nap under 20 minutes boosts alertness without entering deep sleep โ so you wake refreshed. Napping past 30 minutes triggers deep sleep, causing grogginess and disrupting your night.
10โ30 minutes of natural light within 1 hour of waking powerfully sets your circadian clock, improves mood, and makes it easier to fall asleep at night. It's free and one of the most effective interventions.
Human sleep occurs in approximately 90-minute cycles that repeat throughout the night. Each cycle moves through 4 stages: N1 (light sleep onset), N2 (consolidated light sleep), N3 (deep slow-wave sleep), and REM. Waking at the end of a cycle โ during the lightest stage โ means you surface naturally and feel alert. Waking mid-cycle, especially during N3 or REM, causes grogginess known as sleep inertia. We calculate the ideal bedtime by counting backward from your wake time in 90-minute blocks, adding 15 minutes to fall asleep.
No. All calculations on SleepScore happen entirely within your browser. We do not collect, store, transmit, or sell any personal data you enter. Your sleep times and quiz answers never leave your device. See our Privacy Policy for full details.
Yes, 100% free. All features โ the sleep cycle calculator, sleep quality quiz, sleep debt calculator, and all tips โ are fully available at no cost and require no account or sign-up. The site is supported by advertising.
The 90-minute average is well-established in sleep research and applies to most healthy adults. However, individual cycles vary from about 80โ110 minutes and shift throughout the night (early cycles have more deep sleep; later ones more REM). Use the calculator as a helpful guideline โ over a few nights, you'll find the timing that works best for your body.
The National Sleep Foundation recommends 7โ9 hours per night for adults (18โ64 years). This corresponds to 5โ6 complete 90-minute cycles. Older adults (65+) typically need 7โ8 hours. Consistently sleeping less than 7 hours is associated with increased risk of obesity, heart disease, and cognitive decline. The calculator's "Recommended" option targets 7.5 hours โ 5 complete cycles โ as the sweet spot for most people.