Health & Fitness · Free tool
Sleep Calculator
Aligns wake or bedtime to 90-min sleep cycles so you wake during light sleep. Based on Hirshkowitz NSF data.
Aim for one of these bedtimes:
12:46 AM
4 cycles · 6.0h sleep
Minimum — survivable but not ideal long-term
11:16 PM
5 cycles · 7.5h sleep
Good — typical adult target
9:46 PM
6 cycles · 9.0h sleep
Ideal — full restorative sleep
Assumes 90-minute sleep cycles (population average; yours may run 80–110 min) and 14 minutes to fall asleep (Hirshkowitz et al. 2015, National Sleep Foundation). Track your own sleep for a week to calibrate — if you wake naturally at 7:00 most days, your cycle is probably aligned with that schedule.
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What it does
Aligns wake-up time to the end of a 90-minute REM cycle so you wake during light sleep, not deep sleep. Two modes: target wake-up → suggested bedtimes; target bedtime → predicted wake times. Defaults assume ~14 minutes to fall asleep (Hirshkowitz et al. 2015 NSF data).
Embed this tool on your siteShow snippetHide
Paste this snippet into any page. Loads on-demand (lazy), no tracking scripts, and sized to most dashboards. Replace the height to fit your layout.
<iframe src="https://freetoolarena.com/embed/sleep-calculator" width="100%" height="720" frameborder="0" loading="lazy" title="Sleep Calculator" style="border:1px solid #e2e8f0;border-radius:12px;max-width:720px;"></iframe>How to use it
- Pick whether you're solving for wake-up or bedtime.
- Enter the time.
- See 4, 5, and 6-cycle options (6 = ideal, 4 = minimum).
Frequently asked questions
- Are sleep cycles really 90 minutes?
- Population average is 90, but individual cycles range 80–110 minutes. Track your wake-up patterns for a week — if you naturally wake at 7:00 most days from a 11:00pm bedtime, your cycles probably fit that 8-hour span (5.3 cycles ≈ ~91 min average).
- Does this work for naps?
- For naps, aim for either 20 minutes (caffeine-nap territory, no REM) or 90 minutes (one full cycle). 30–60 minute naps wake you mid-cycle and tend to feel groggy.
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Learn more
Guides about this topic
- How-To & Life · GuideHow to Sleep BetterSleep better tonight: ten habits that move the needle on sleep quality, without melatonin marketing.
- How-To & Life · GuideHow to Drink More WaterDrink more water without thinking about it: habit stacks, bottle tricks, and signals to watch for.
- How-To & Life · GuideBeginner Workout Plan at HomeA 4-week home workout for complete beginners. Bodyweight only, 20-30 minutes, three days a week.
- How-To & Life · GuideHow to Start RunningStart running without hating it. A walk-run plan to your first 5K in 8 weeks, plus injury avoidance.
- How-To & Life · GuideHow to Lose Belly FatYou can't spot-reduce. What actually works: calorie deficit, strength, sleep, stress. Honest and boring.
- How-To & Life · GuideIntermittent Fasting for BeginnersIF explained simply: 16:8, what to eat, common mistakes, and who should skip it. No hype.
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