health100% Browser-Based

Sleep Calculator

A smart Sleep Calculator that uses the science of 90-minute sleep cycles to find your ideal bedtime or wake-up time. Enter when you need to wake up and we'll suggest bedtimes that let you complete 4–6 full sleep cycles (plus time to fall asleep). Or enter your bedtime to find the best times to wake. All calculations happen in your browser — private and mobile-friendly.

What do you want to calculate?

Wake Time (24h)

Target Sleep Cycles5 × 90 min

3 (4.5h)5 (7.5h)7 (10.5h)

To wake at 7:00 AM

2:16 AM

3 cycles · 4.5 hours

12:46 AM

4 cycles · 6 hours

11:16 PMRecommended

5 cycles · 7.5 hours

9:46 PMRecommended

6 cycles · 9 hours

Waking at the end of a full 90-minute cycle leaves you more refreshed. Sleep needs vary by age and lifestyle — 5–6 cycles (7.5–9h) suits most adults. This is guidance, not a medical recommendation.

Frequently Asked Questions

Everything you need to know about sleep cycles and timing

How does the sleep calculator work?

Sleep follows cycles of about 90 minutes. Waking up at the end of a full cycle (rather than mid-cycle) leaves you feeling more refreshed. We work backward from your wake time (subtracting 90-minute cycles plus ~14 minutes to fall asleep) or forward from your bedtime.

How many sleep cycles do I need?

Most adults function best on 4–6 cycles (6–9 hours of sleep). We recommend aiming for 5–6 cycles. Consistently getting fewer than 4 cycles (under 6 hours) is linked to health risks over time.

What's the best bedtime?

It depends on your wake time and chronotype. The calculator suggests bedtimes that let you complete full cycles before your wake time. Pick one that fits your schedule and stick to a consistent routine — consistency matters as much as the exact time.

Is my data private?

Yes. Everything runs in your browser. Your sleep schedule never leaves your device.

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Runs in your browser100% privateNo data uploaded