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Nap Calculator

Best nap wake-up times (or lie-down times) across common nap lengths, adding the time to fall asleep.

Related tools

All Sleep & alertness tools →
Coffee vs. Sleep CalculatorA transparent heuristic that scores a coffee against a nap for the alertness you need right now.Caffeine intake calculatorEstimate a safe daily caffeine limit for a healthy adult.Sleep cycle calculatorFind the best bedtimes to wake up refreshed, based on 90-minute sleep cycles.Alcohol Calorie CalculatorAdd up the calories of a drinking session from a library of beers, wines, spirits and cocktails, with a custom-drink option.Am I Overweight? CalculatorFind out if you're overweight from your BMI, with your healthy weight range and kg to reach it.Am I Underweight? CalculatorFind out if you're underweight from your BMI, with your healthy weight range and kg to reach it.Baby Growth Percentile CalculatorWeight, length and head circumference percentiles from the WHO Child Growth Standards, 0-24 months.Baby Milk Intake CalculatorBottle volumes per feed and per day by your baby's weight and age, with the feeding interval.

Open Nap Calculator and you get an answer straight away, with no account to create. It sits under Sleep & alertness in our catalogue, alongside Coffee vs. Sleep Calculator and Caffeine intake calculator.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What is Nap Calculator?

Best nap wake-up times (or lie-down times) across common nap lengths, adding the time to fall asleep.

When would I actually use this?

Working backwards from the hour you have to be up: when to go to bed so an alarm does not land in the middle of deep sleep, how long a nap can run before it starts costing more than it gives, and how late a coffee still counts.

What is the most common mistake?

Treating the cycle length as a fact about you. Ninety minutes is an average, and a real cycle runs anywhere from about seventy to a hundred and ten minutes and changes across the night — so a bedtime computed here is a better guess than the round hour, not a wake-up guarantee. The time it takes to fall asleep is the other half, and it is the part people leave out.

How is Nap Calculator different from Coffee vs. Sleep Calculator?

They sit next to each other but answer different questions: Coffee vs. Sleep Calculator is the one to open when you need it to a transparent heuristic that scores a coffee against a nap for the alertness you need right now. Pick whichever matches what you're starting from — both are free.

Where do the figures come from?

Sleep architecture — the ninety-minute cycle, the share of deep sleep early in the night and of REM towards morning — is textbook sleep medicine, and the tools apply it as arithmetic on the hour you give them. Caffeine is modelled on its half-life, around five to six hours in a typical adult, which is why an afternoon cup is still measurably present at bedtime; that half-life varies with genetics, pregnancy, liver function and some medicines, by a factor no calculator can guess. None of this diagnoses insomnia or any other sleep disorder — persistent trouble sleeping is worth a clinician, not an arithmetic.

Further reading

All guides →
ExplainerNap Length Decides What You Get — Not How Tired You WereA nap's effect depends on which sleep stage the alarm interrupts, and length is the only part of that you control. What 10, 20, 30 and 90 minutes actually do, with the arithmetic for the alarm.ExplainerCaffeine Against Sleep Pressure: What It Blocks, and What It CannotSleep is regulated by two processes: a pressure that builds with every waking hour, and a clock. Caffeine acts on neither directly — it blocks the receptors that report the pressure. The pressure keeps building behind the block, which is why the crash arrives and why an afternoon dose costs that night's sleep even when you do not feel it.ExplainerCaffeine Half-Life: Why Your Afternoon Coffee Is Still There at MidnightCaffeine leaves by first-order kinetics, so what remains is the dose times one half to the power of elapsed time over half-life. The half-life is not a constant — it varies by multiples between people, and that is the whole story.ExplainerHow Much Milk Does a Baby Need? The Rule of Thumb and Its LimitsA formula-fed baby takes roughly 2.3 fl oz per pound of body weight per day in the first months, split across the day's feeds. Here is the table by age and weight, why breastfed babies are not measured this way, and the signs that outrank any number.ExplainerAm I Overweight? Why One Number Cannot SayBMI reads muscular bodies as heavy and cannot see where fat sits at all — which is exactly why the waist measures exist. Here are the published waist and waist-to-height thresholds, a worked case where BMI and waist give opposite answers, an honest account of the contested mortality curves, and the 2025 shift toward defining obesity by adiposity and organ function rather than by a ratio.ExplainerAm I Underweight? What the Question Is Really AskingThe 18.5 cut-off is a population screening line, not a diagnosis. Here is where it comes from, what the mortality data below it actually show, and the three things it cannot see: body composition, recent change — which is far more informative than the level — and the fact that the same line does not fit every age or every population.