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Deep Sleep Estimate Calculator

Enter your sleep hours and age to estimate your deep sleep.

How it is calculated

The tool does not read any sleep data. It assumes that deep sleep is 20% of a night at age 20 and changes by 0.3 percentage points for every year of age: share % = 20 − (age − 20) × 0.3. That share is kept between 5% (reached at age 70) and 25% (reached only below about age 3½), and then deep sleep = hours × share ÷ 100, shown in hours and in whole minutes. Hours of sleep must be above 0 and at most 14, and age above 0 and at most 100; other values give no result. The percentage is a straight-line population average, so it ignores how well you slept, alcohol, illness and individual differences. Compare it with a tracker's stage report only as a rough guide: it is not a measurement and not a diagnosis.

Worked example

A 45-year-old sleeps 7.5 hours. Share of deep sleep: 20 − (45 − 20) × 0.3 = 20 − 7.5 = 12.5%. Deep sleep: 7.5 × 12.5 ÷ 100 = 0.94 h, which is 56 min. The same person at 20 would be estimated at 20.0% of 7.5 hours, or 90 min, and at 80 the share sits at the 5.0% floor, about 23 min for the same 7.5 hours. If a tracker shows far more or less than 56 minutes for you, that alone says little, since devices estimate stages with their own error.

Try this example →

Common mistakes

  • Entering time in bed instead of time asleep. The calculation applies the share to hours of sleep, so a long period lying awake inflates the answer.
  • Typing sleep time as 7:30. Use a decimal number, so 7 hours 30 minutes is 7.5; a total above 14 hours gives no result.
  • Comparing a single night with the estimate. The figure is an age-based average, and one night can differ a lot without meaning anything.
  • Treating the result as a diagnosis or a target to chase. It is a population-based estimate, not a measurement of your own sleep.
  • Expecting the share to keep falling forever. It stops at 5% from age 70, so an 80-year-old and a 95-year-old get the same percentage.

Sources

About this calculator

Deep sleep, also called slow-wave sleep or stage N3, is the stage of the sleep cycle marked by the slowest brain waves and the point where you are hardest to wake — it is when the body does most of its physical repair and immune maintenance. In healthy young adults it is often quoted at somewhere around 13 to 23% of total sleep time, but that share falls steadily with age, and by the senior years deep sleep can shrink to only a small fraction of what it was in youth.

This calculator assumes deep sleep is about 20% of your sleep at age 20 and falls by about 0.3 percentage points for each year of age, never going below 5% or above 25%, and applies that share to your reported total sleep hours to estimate how much of your night is likely spent in deep sleep, which is useful context for anyone reading a sleep tracker's stage breakdown and wondering whether their deep sleep percentage looks typical for their age rather than comparing themselves to a flat, one-size-fits-all target. It is an estimate based on population averages, not a diagnostic measurement — actual deep sleep varies with individual physiology, sleep quality, and can only be measured precisely with polysomnography.

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