Key answer

Choose “Take a nap,” enter your local nap start time, select a nap length, and adjust “Time to fall asleep” under Advanced settings. The calculator adds settling time and nap duration to show an estimated alarm time. It does not start a timer, ring an alarm, or detect when you fall asleep.

1. Enter when you plan to start

Open the Nap Calculator. The “Take a nap” mode is selected on that page. The “Nap start time” is when you plan to lie down, before the settling allowance. Check the local time rather than assuming the prefilled time matches your plan.

2. Choose a nap length

The current options are 20, 30, 60, 90 and 120 minutes. The default is 90 minutes. That default is an arithmetic starting point, not advice that everyone needs a 90-minute nap or that it will complete a biological cycle.

For a short daytime rest, the 20-minute option may be more appropriate than a long cycle-based plan. NHLBI recommends short adult naps, and NIOSH discusses short naps for alertness. The power-nap guide explains the practical tradeoffs.

3. Review Advanced settings

  • Time to fall asleep: the default is 15 minutes. Choose an available allowance that is realistic for you; it is added before the selected nap duration.
  • Date: optional. Use it when the date matters, such as a calculation around a daylight-saving change. Confirm the result's displayed date and time.
  • Use 24-hour results: changes the time display, not the calculation.

The cycle-length slider is hidden in nap mode because this mode uses your selected duration directly. It does not measure or optimize the stages inside that duration.

4. Read the result, then set your alarm

With a 1:00 PM start, 10 minutes to fall asleep and a 20-minute nap, the estimated alarm time is 1:30 PM. The summary distinguishes the settling allowance from the time planned for sleep. The displayed date helps when a calculation crosses midnight.

The formula is start time + settling allowance + nap length. If you have only 20 minutes total, adding a settling allowance to a 20-minute nap will exceed that break. Use a simple device alarm within your actual time limit rather than treating estimated sleep as guaranteed.

Try a 20-minute nap estimate

This opens the short-nap option with a 10-minute settling allowance. Enter your own start time before calculating.

Plan a short nap

What the controls do after calculating

“Copy share link” copies a URL containing the chosen timing inputs when clipboard access is available. Reset clears the result and returns the nap duration and settling allowance to their defaults. Neither action sets an alarm or sends a wake-up notification. A fresh calculation is needed after changing inputs.

What the result cannot tell you

A duration labelled as estimated cycles is not a stage reading. Sleep inertia can still occur, so allow time to become alert before demanding tasks. Keep adequate nighttime sleep in view with adult sleep-duration guidance; the tool is a planning aid for adult-style schedules, not infant or child sleep guidance.

Related reading

How long should a power nap be?What are sleep cycles?What is sleep debt, and can you recover it?

Sources

  1. NIH / NHLBI: Sleep Deprivation and Deficiency: Healthy Sleep Habits. Accessed September 8, 2026.
  2. CDC / NIOSH: Napping, an Important Fatigue Countermeasure: Nap Duration. Accessed September 8, 2026.
  3. CDC / NIOSH: Napping, an Important Fatigue Countermeasure: Sleep Inertia. Accessed September 8, 2026.

Editorial review by SnoozeCalc; not medical review. Sources and calculator assumptions were checked on September 8, 2026. Read our editorial policy and medical disclaimer.