The Bedtime Calculator

Wake up refreshed,
not groggy.

Sleep tends to run in cycles of about 90 minutes. Wake near the end of one and you're more likely to feel refreshed; wake mid-cycle and grogginess can linger. Tell us when you need to be up and we'll suggest bedtimes that line up with the math.

AASM & NSF guideline-aligned Free, no signup
7:00 AM

Based on natural 90-minute sleep cycles + 15-min fall-asleep buffer

The science · 2 min read

Why when you wake up matters — not just how long you sleep.

Each night you cycle through light sleep, deep sleep, and REM in roughly 90-minute loops. Wake near the top of a cycle — when sleep is lightest — and getting up tends to feel easier. Get jolted awake mid-deep-sleep and you can fight grogginess (sleep inertia) for anywhere from a few minutes to an hour or more.

Most adults need 5–6 complete cycles — about 7.5 to 9 hours. Our calculator picks bedtimes that land you at the natural end of one, with a 15-minute buffer for falling asleep.

6h
4 cycles · Short night, not a target
7.5h
5 cycles · Sweet spot · most adults
9h
6 cycles · Recovery & catch-up nights
4.5h
3 cycles · Power-through nights
Recommended sleep · by age

How much sleep do you actually need? It depends on your age.

See all age guides
0–3 months
Newborns
14–17h
Calculate
4–11 months
Infants
12–15h
Calculate
1–2 years
Toddlers
11–14h
Calculate
3–5 years
Preschool
10–13h
Calculate
6–13 years
School age
9–11h
Calculate
14–17 years
Teens
8–10h
Calculate
Popular wake-up times

Pick a wake-up time and get the bedtime that lands you on the cycle.

Wake at
5:00 AM
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Wake at
5:30 AM
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Wake at
6:00 AM
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Wake at
6:30 AM
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Wake at
7:00 AM
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Wake at
7:30 AM
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Wake at
8:00 AM
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Wake at
9:00 AM
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Frequently asked

Common bedtime questions, answered.

How does the bedtime calculator work?
We use the standard 90-minute sleep cycle model: most people complete a full cycle of light, deep, and REM sleep every 90 minutes. We add a 15-minute buffer to fall asleep, then count backwards from your wake-up time to find bedtimes that land you at the natural end of a cycle.
What time should I go to bed if I want to wake up at 6 AM?
For a 6 AM wake-up, the calculator recommends bedtimes of 8:45 PM (6 cycles / 9h), 10:15 PM (5 cycles / 7.5h), or 11:45 PM (4 cycles / 6h). Most adults feel best with 5 cycles.
Is 6 hours of sleep enough?
Six hours is roughly four 90-minute cycles — below the 7+ hours most adults need. You'll function, but research consistently shows cognitive and immune trade-offs versus 7–9 hours. Treat 6h as a short-night fallback, not a target.
Why do I feel groggy when my alarm wakes me up?
That's sleep inertia — your alarm interrupted a deep-sleep stage. Waking near the end of a cycle can ease it for many people. Sunrise alarms also help, since they signal your brain to begin the wake-up process gradually.
Are sleep cycles really exactly 90 minutes?
It's an average. Cycles range 70–120 minutes between individuals and even within a single night (early cycles tend toward deep sleep, later ones toward REM). 90 minutes is a useful planning average — you may want to test ±15 min to find your personal length.
Does this work for night-shift workers?
Yes — the cycle math is the same regardless of clock time. The bigger issue for shift workers is light exposure. Pair the calculator with blackout curtains and consistent wake-up times, even on days off.
Sources The New York Times· Healthline· WebMD· Forbes Health· Mindbodygreen· Sleep Foundation