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● Pregnancy & wellness

Find your perfect bedtime by sleep cycles.

Wake up refreshed — not groggy — by timing your sleep to end at the right point in a 90-minute cycle. Enter your desired wake time or bedtime and get 4–6 color-coded options.

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Sleep Calculator — Optimal Bedtime & Wake Time
90-minute cycle timing · NSF age recommendations · Night timeline
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Your sleep parameters

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Recommended times

NSF recommended sleep for your age
7–9 hours
Equivalent to 5–6 complete 90-min cycles
Ideal bedtimes to wake at 07:00:
Enter a time above to see options
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How it's calculated

Sleep cycles, not just hours

The Sleep Calculator finds the ideal bedtime or wake time by counting backwards or forwards in 90-minute sleep cycle increments. A 14-minute sleep onset latency is added to each option to account for the average time it takes a healthy adult to fall asleep. For example, to wake at 7:00 AM after 5 cycles (7.5 h) you should be in bed by 11:16 PM. Green options fall within the NSF-recommended range for your age group.

Every night your brain passes through alternating NREM (N1→N2→N3) and REM stages in roughly 90-minute blocks. Waking mid-cycle — especially during deep N3 — triggers sleep inertia, the groggy, disoriented feeling that can last 30–60 minutes. Waking at the end of a cycle, when you naturally surface to light N1 sleep, dramatically reduces this.

Bedtime = Wake time − (Cycles × 90 min) − 14 min onset
Wake time = Bedtime + 14 min onset + (Cycles × 90 min)
  1. 1
    Take your target time (wake or bed)
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  2. 2
    Add 14 min sleep onset latency (SOL)
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  3. 3
    Step back/forward in 90-min increments (3–6 cycles)
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  4. 4
    Color-code by NSF recommendation for your age
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Understand the terms

Sleep cycle
One complete pass through NREM (N1, N2, N3) and REM stages, lasting approximately 90 minutes. Adults complete 4–6 cycles per night.
REM (Rapid Eye Movement)
The stage associated with vivid dreaming, memory consolidation and emotional processing. REM periods lengthen toward morning.
NREM (Non-REM)
Three stages: N1 (light, transition), N2 (body temperature drops, heart rate slows), N3 (deep slow-wave — the most restorative stage).
Circadian rhythm
The internal ~24-hour biological clock that regulates sleepiness and alertness, driven by light exposure and core body temperature.
Sleep debt
The cumulative shortfall between sleep needed and sleep obtained. Cannot be fully recovered in one night and impairs cognition, metabolism and immunity.
See the full glossary →
Disclaimer: estimation tool for informational and planning purposes. The 90-minute cycle and 14-minute SOL are population averages — individual cycle length (70–120 min) and onset latency vary significantly. Sleep recommendations follow NSF 2015/2023 guidelines. This tool does not replace evaluation by a physician or sleep specialist.
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Frequently asked questions — Sleep Calculator

How does the Sleep Calculator work?
The calculator works backwards (or forwards) from your chosen time in 90-minute increments — the average duration of one complete sleep cycle. It adds 14 minutes to account for the time it typically takes to fall asleep (sleep onset latency). Completing full cycles means you wake at the lightest stage, reducing grogginess.
How many hours of sleep do adults need?
The National Sleep Foundation recommends 7–9 hours for adults (18–64 years), 7–8 hours for older adults (65+), 8–10 hours for teenagers (14–17), and 9–11 hours for school-age children (6–13). Individual needs vary, and consistently waking refreshed is the best indicator.
What is a sleep cycle?
A sleep cycle lasts approximately 90 minutes and includes four stages: three NREM stages (N1 light, N2 intermediate, N3 deep/slow-wave) followed by REM (rapid eye movement) sleep. Each cycle progressively shifts toward more REM sleep in the second half of the night.
Why do I feel groggy even after 8 hours of sleep?
Grogginess — called sleep inertia — typically occurs when you wake mid-cycle during deep (N3) sleep. By timing your alarm to fall at the end of a complete 90-minute cycle, you wake during lighter N1 or N2 sleep, which dramatically reduces morning grogginess.
What is sleep debt and how do I calculate it?
Sleep debt is the cumulative difference between the sleep you need and the sleep you get. For example, getting 6 hours when you need 8 creates 2 hours of sleep debt per night. Chronic sleep debt is associated with impaired cognition, weakened immunity and increased metabolic risk. The only way to repay it is by sleeping more over subsequent nights.

📚 Learn more — official sources

🏛️ Organization National Sleep Foundation — Sleep recommendations by age The NSF publishes evidence-based sleep duration recommendations for each age group, from infants to older adults, updated annually. See official source → 🏛️ Organization AASM — Recommended amount of sleep for a healthy adult American Academy of Sleep Medicine consensus statement recommending at least 7 hours of sleep per night for adults to promote optimal health. See official source → 🏛️ Organization CDC — How much sleep do I need? Centers for Disease Control and Prevention guide on recommended sleep hours by age group and the health consequences of insufficient sleep. See official source → 🔬 Study NIH — Sleep, sleep disorders and biological rhythms Comprehensive NIH science education module covering sleep stages, circadian rhythms and the biological mechanisms that regulate the sleep-wake cycle. See on NIH →

About the Sleep Calculator

The Sleep Calculator uses the science of sleep cycles to help you time your rest for maximum refreshment. Rather than simply counting hours, it calculates bedtimes or wake times that land at the natural end of a 90-minute cycle — the point where your brain transitions back to light sleep and waking is easiest.

The 14-minute sleep onset figure comes from population studies of healthy adults (Walker, 2017; NSF data). Color coding is based on the National Sleep Foundation's age-specific guidelines: green options fall within the recommended range, yellow are slightly below or above, and red options represent fewer than 4 cycles or chronically insufficient sleep.

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