Sleep calculator: what time should I go to bed?

A sleep cycle calculator that aims for the end of a cycle

This sleep calculator answers two late-evening questions: “what time should I go to bed to feel rested?” and, once you are under the covers, “what should I set the alarm for?”. It counts whole sleep cycles, adds the time you take to drift off and lists the times that land at the end of a cycle. A third mode works as a wake up time calculator for naps. Everything runs in your browser, in 12-hour time (9:45 PM), and crossing midnight is handled.

How to use it

1. Pick a mode: “I want to wake up at…”, “I'm going to bed at…” or “Nap”.
2. Enter the time. For bedtime and naps, the “Now” button fills in the current time.
3. Adjust “Cycle length (min)”, 90 by default, from 80 to 110, and “Time to fall asleep (min)”, 15 by default, from 0 to 60, if you like.
4. Read the “Suggested bedtimes” or “Suggested wake-up times”. The 5-cycle and 6-cycle options are tagged “Recommended”; a bedtime already behind you is marked “Already passed”.
5. Click a time: the timeline shows the night cycle by cycle, and you can “Copy time” or “Download a reminder (.ics)”. Nothing is sent.

Worked examples

With the default settings: wake-up time, minus 15 minutes, minus the number of cycles × 90 minutes. Say you need to be up at 6:00 AM to beat the commute:

The other way round: in bed at 11:00 PM, you get 3:45 AM (3 cycles), 5:15 AM (4), 6:45 AM (5) and 8:15 AM (6).

Sleep cycles in plain words

Each cycle moves through light sleep, deep sleep, when the body does most of its recovery, and REM sleep, the stage linked with vivid dreams. A cycle often lasts about 90 minutes, but this differs between people, which is why the length can be set from 80 to 110 minutes. Deep sleep fills more of the early night and REM grows towards morning, as the timeline shows in a simplified way.

Being woken from deep sleep tends to leave you groggy. Aiming for the end of a cycle, when sleep is lighter, may help you get up more easily. Treat it as a practical rule of thumb, not a scientific guarantee.

How much sleep you need by age

Widely cited public health guidelines give these general ranges: 9 to 12 hours for children aged 6 to 12, 8 to 10 hours for teenagers and 7 to 9 hours for adults. Individual needs vary.

Naps and healthy habits

The “Nap” mode shows two wake-up times: a “Short nap” of 10, 15 or 20 minutes keeps you in light sleep, the classic power nap, while a “Full cycle” helps after a short night. Lie down at 1:30 PM with 5 minutes to fall asleep and you wake at 1:55 PM after 20 minutes, or at 3:05 PM after a 90-minute cycle. Avoid late-afternoon naps.

To sleep better: keep regular hours, weekends included, get daylight in the morning, dim the lights in the evening, put screens away an hour before bed and skip caffeine later in the day. If sleep problems last for several weeks, see a doctor.

Frequently asked questions

Why does the calculator add 15 minutes?

Cycles only start once you are asleep. Set “Time to fall asleep (min)” to 0 to count from the moment you are sleeping.

Is 5 or 6 cycles better?

For an adult, 5 cycles (7 h 30 min) or 6 cycles (9 hours) both fit the 7 to 9 hour range. Four cycles will get you through one night, not week after week.

Do my cycles really last 90 minutes?

Not necessarily; it is an average. If you often wake just before the alarm, shorten it a little. Otherwise, try another value in “Cycle length (min)” for a few days and keep the one that leaves you most refreshed.

Will the .ics file ring like an alarm?

It adds a 5-minute calendar event with an alert, usually a plain notification. If you must not oversleep, copy the time into your clock app. Your last settings stay on this device.