Sleep cycles

Updates automatically as you type.

Calculated in your browser; your inputs are not sent to us. Privacy

Results will appear here.

General estimate for planning only — not medical advice. Consult a doctor about your specific situation.

Calculation details

Every figure above is calculated locally in your browser from the assumptions shown. No inputs are sent anywhere. See the methodology section below for how this tool works.

Use this resultShare the current inputs, or ask ChatGPT to explain the calculation in context.

Ask an AI to explain this result

Review the generated output before relying on it.

This tool runs in your browser. Your calculator inputs and results are never transmitted to us or to ad/affiliate partners. Ads and sponsored links may set third-party cookies to serve and measure them, but they never receive your calculation values. If you explicitly save a scenario, its permitted fields stay in local browser storage until you clear them. See our Privacy Policy.

Use this result

Share the current inputs or ask ChatGPT to explain the calculation in context.

Include calculator values in URL

More options

Report a calculation issue

Bar chart of bedtime length in minutes by sleep cycles — 5 cycles plus 15 minutes adds up to 7h 45m in bed.

Method & verification

How This Tool Works

fact-checked against our calculation methodology

Calculation Method

Computes Sleep duration from Sleep cycles.

Site methodology

BoringToolsKit methodology and verification standard

No unrelated authority link is added merely to make this page look sourced. Tool-specific external sources are shown only when they directly support the method, rate, or rule.

Assumptions to Verify

These tools provide general estimates for planning and education only.
They are not medical advice and not a substitute for a qualified healthcare professional.
Always consult your doctor or another healthcare provider about your specific situation.

Privacy: The calculation runs in this browser. Shared links contain the page address only, not your inputs or results.

Worked example: 5 cycles

Set cycles to 5. The formula runs: 5 x 90 = 450 minutes of cycle sleep, plus the 15-minute sleep-onset allowance, so mins = 465. Split that into hours and minutes: 465 / 60 is 7 with a remainder of 45, so the result reads 7h 45m.

That 7h 45m is time in bed, not time asleep. Of it, 450 minutes (7h 30m) is counted sleep and 15 minutes is the assumed drift-off period. Five full cycles also means you wake at a cycle boundary, which is why the tool counts in whole cycles instead of free-form hours: waking mid-cycle, around minute 40 of 90, tends to feel worse than waking after the same total time.

Cross-check against common advice: the often-quoted 7.5 to 9 hours corresponds to 5 cycles (7h 45m here) and 6 cycles (6 x 90 + 15 = 555 minutes = 9h 15m).

Where the numbers break down

The 90-minute cycle length is an average, not a constant. Measured cycles commonly run roughly 80 to 120 minutes, and they lengthen in later sleep. For a true 105-minute cycle, 5 cycles is 525 minutes asleep; the tool would report 7h 45m in bed, about 75 minutes short.

The 15-minute sleep latency is likewise a fixed assumption. Healthy adults average around 10 to 20 minutes, but stress, caffeine, or screens can push latency past 30 minutes. If you take 45 minutes to fall asleep, a 5-cycle plan computed here lands you 30 minutes before your intended wake time, cutting the last cycle short near a bad waking point.

Practical use: pick a bedtime that lets you fall asleep at the planned time, count back in whole 90-minute blocks from your fixed wake time, and adjust after a few nights rather than trusting one night's arithmetic. If you consistently wake groggy at a predicted boundary, shift by 15 to 20 minutes instead of adding a full cycle.