Recovery

Sleep Calculator

Calculate the best times to sleep and wake up based on natural sleep cycles. Plan 4-6 complete cycles for better rest.

Best bed times

Sleep Duration Ladder

More cycles increase total sleep opportunity, with the strongest windows clustered at the top.

3 cycles

02:15 -> 07:00

4h 45m

4 cycles

00:45 -> 07:00

6h 15m

5 cycles

23:15 -> 07:00

7h 45m

6 cycles

21:45 -> 07:00

9h 15m

0h10h

3 cyclesShort

Bed

02:15

Sleep time

4h 45m

4 cyclesGood

Bed

00:45

Sleep time

6h 15m

5 cyclesIdeal

Bed

23:15

Sleep time

7h 45m

6 cyclesIdeal

Bed

21:45

Sleep time

9h 15m

💤 Disclaimer: This calculator is based on the 90-minute sleep cycle hypothesis. Individual sleep needs vary. Optimal sleep depends on age, health, activity level, and personal factors. Use this as a general guide and consult healthcare professionals for personalized advice.

How to use it

Enter your required wake time or target bedtime. The calculator outputs optimal sleep start times based on 90-minute sleep cycles — waking mid-cycle (not at cycle end) causes sleep inertia and prolonged morning grogginess.
Target 5–6 complete cycles (7.5–9 hours). Fewer than 4 cycles (<6 hours) consistently impairs muscle protein synthesis, growth hormone release, fat oxidation, and cognitive performance.
If you sleep the recommended hours but still wake tired, you likely have a sleep quality issue: alcohol within 3 hours of bed fragments deep sleep, screen light delays melatonin onset by 30–60 minutes, and inconsistent timing disrupts circadian rhythm.
Sleep schedule consistency matters as much as duration. Varying bedtime by more than 60 minutes across the week degrades sleep quality even at adequate total hours — prioritize a consistent wake time above all else.
During high-intensity training blocks, aim for 8–9 hours. Chronic short sleep (6 hours/night for 2 weeks) has been shown in research to reduce strength gains and muscle recovery equivalent to the effect of 24 hours of total sleep deprivation.

AI Integrations

Contract, discovery endpoints, and developer notes for agent use.

Always available for agents

Tool contract JSON

https://aifithub.io/contracts/sleep-calculator.json

Stable input and output contract for this exact tool.

Human review

People can use the browser page to sense-check outputs and charts, but agents should still execute against the contract and discovery endpoints.

/agent-tools.json - machine-readable tool index.
/llms.txt - human-readable model discovery guide.
/.well-known/webmcp.json - WebMCP capabilities manifest.
/.well-known/ai-plugin.json - plugin-style discovery manifest.

{
  "tool": "sleep_calculator",
  "wake_time": "06:30",
  "sleep_cycles": 5
}

Open tool contract JSON Open AI integrations guide

Expand developer notes

Agent playbook

Resolve Sleep Calculator from /agent-tools.json and open its contract before execution.
Validate inputs against the contract schema instead of scraping labels from the page UI.
Open the browser page only when a person wants to review charts, assumptions, or related tools.

Agent FAQ

Should ChatGPT, Claude, or another agent click through the UI?

No. Start with /agent-tools.json, then follow the tool's contract URL. The page UI is for human review, not parameter discovery.

When do tools show Quick and Advanced?

Every tool opens in Quick Start first. Advanced Controls keeps the same scenario, reveals more assumptions or diagnostics, and every tool keeps AI integrations inline below the instructions.

When should an agent still open the browser page?

Open it when a human wants to sense-check the output, review the chart, or keep exploring related tools after the calculation finishes.

Questions people usually ask

What is a sleep cycle?

A sleep cycle is approximately 90 minutes and includes different stages: light sleep, deep sleep, and REM sleep. Your body naturally completes cycles in roughly 90-minute intervals.

Why does 90 minutes matter?

Waking up at the end of a complete cycle (rather than in the middle) can help you feel more rested. 4-6 complete cycles typically results in 6-9 hours of sleep, which is the recommended range for most adults.

What do the ratings mean?

Ideal = 5-6 cycles (7.5-9+ hours), Good = 4 cycles (~6.5 hours), Short = 3 cycles (~5 hours). Aim for ideal when possible, but any complete cycle is better than waking mid-cycle.

How do I account for the time it takes to fall asleep?

This calculator includes a fall-asleep time (default 15 minutes). If you typically fall asleep faster or slower, adjust the slider to match your experience for more accurate results.

Can I use this if I work night shifts?

Yes! The calculator works for any 24-hour time. Just enter when you want to wake or sleep, regardless of whether it's day or night.

Is this medical advice?

No. This tool provides general sleep optimization guidance based on the 90-minute cycle hypothesis. Sleep needs vary by age, health, and lifestyle. Consult a healthcare provider for personalized sleep advice.

Is this tool free and private to use?

Yes. AI Fit Hub tools are free, no-signup browser tools. Inputs stay in your browser unless you choose to share a URL.

Do these tools replace medical guidance?

No. These outputs are general fitness estimates — not medical advice.

Can I switch between metric and imperial units?

Yes. Every tool supports both systems and remembers your preference in localStorage.

Related Resources

Learn the decision before you act

Every link here is tied directly to Sleep Calculator. Use the explanation, formula, examples, and benchmarks to pressure-test the calculator output from first principles.

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Guides · 3 Checklists · 5 Comparisons · 1 Tips · 14 Mistakes · 8

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