Sleep Cycle Calculator (90-Minute Cycles)

1. Enter when you go to bed. Use the time you lie down to sleep. Nights across midnight work automatically.
2. Add how long it takes to fall asleep. Cycles start once you are asleep, so this shifts every wake time.
3. Pick a cycle length and age group. 90 minutes is typical; choose longer if you usually wake groggy at the 90-minute times.

Need to work backwards from a fixed alarm instead? The bedtime calculator does that.

A sleep cycle is one pass through the stages of sleep: light stage 1, stage 2, deep stage 3 and REM sleep. A full cycle takes roughly 90 to 110 minutes, and most adults go through 4 to 6 cycles a night.

The cycles are not identical. REM periods get longer later in the night, and the first REM period starts about 90 minutes after falling asleep. The stages of sleep guide explains each stage in detail.

The idea behind the calculator is to time your alarm for the light sleep at the end of a cycle, rather than the middle of deep sleep, which may leave you groggier.

It adds the time to fall asleep to your bedtime, then adds whole cycles.

The best wake-up time is the cycle count whose sleep falls inside the recommended range for your age, closest to the middle of that range.

Both 5 and 6 cycles fit the adult range of 7 to 9 hours; 5 cycles is closer to the middle. A 5:15 AM alarm would end a cycle too, but 6 hours is short for most adults.

If you fall asleep about 15 minutes after going to bed, these are the wake-up times at the end of 4, 5 or 6 full 90-minute cycles. Most adults should aim for 5 or 6.

Going to sleep right now? Choose “Right now” in the calculator and it uses the current time.

Cycles average about 90 minutes but run from roughly 90 to 110 minutes, and yours may sit anywhere in that range. You can estimate your own in two ways.

1. Use free mornings. On 3 or more days off, go to bed at a normal time and wake without an alarm. Note how long you slept, minus the time it took to fall asleep.
2. Divide by whole cycles. Divide that sleep time by 5 (or by 4 or 6 if that gives a number closer to 90 to 110). 7 h 40 min of sleep is 460 minutes; 460 / 5 = 92 minutes per cycle.
3. Or test the settings. Use the 90, 100 and 110 minute options above for a few nights each and keep the one that leaves you least groggy.

This is an estimate, not a measurement. Only a sleep study records your real cycles, and their length also changes through the night.

Cycle Length

Cycles vary between people and through the night, from about 90 to 110 minutes. If 90-minute times leave you groggy, try 100.

Time To Fall Asleep

Stress, caffeine and screens late in the evening push every cycle later; the caffeine calculator shows how late coffee affects you.

Night Wakings

Waking in the night resets the timing, so later cycles may not line up.

Age

Older adults spend less time in deep sleep and REM, and sleep need changes with age.

Always get enough sleep first, then use cycle timing to pick a wake-up time within that range.

• People who wake up groggy despite enough sleep.
• Anyone choosing a bedtime-to-alarm plan for tonight.
• Shift workers and travellers fitting sleep into odd hours.
• Teens, who need 8 to 10 hours and often sleep too little.

Choosing Too Few Cycles

Four cycles of 90 minutes is only 6 hours, short for most adults.

Forgetting Time To Fall Asleep

Cycles start when you are asleep, not when you lie down.

Treating 90 Minutes As Exact

Real cycles vary, so the time is a target, not a guarantee.

Snoozing

Repeated snoozing breaks up the last part of the night. Set one alarm at the time you mean to get up.

The arithmetic is exact, but real cycles vary in length, so the wake times are estimates.

About 90 to 110 minutes. Most adults complete 4 to 6 cycles in a night.

With 15 minutes to fall asleep and 90-minute cycles, 6:45 AM after 5 cycles, or 8:15 AM after 6.

For most adults 7.5 hours is better. It meets the 7 to 9 hour recommendation, while 6 hours falls short.

It may reduce grogginess, because waking from deep sleep can make it worse, but the evidence is mixed. Getting enough total sleep matters more.

Most adults need about 5 cycles. Teens often need 6.

Night wakings shift the timing, so later cycles may not match the calculator.

Cycle length varies, you may be short on total sleep, or something else such as sleep apnea may be disturbing your sleep.

No. Cycles average about 90 to 110 minutes, vary between people and change through the night, so treat the wake time as a target and adjust by 10 to 15 minutes.

Choose Right now in the calculator. It adds your minutes to fall asleep and shows wake times after 4, 5 and 6 full cycles from the current time.

For naps, the nap calculator is a better fit: short naps of 20 to 30 minutes avoid deep sleep.

• StatPearls: Physiology, Sleep Stages (cycles of 90 to 110 minutes)
• NINDS: Brain Basics: Understanding Sleep (stages, first REM at about 90 min)
• National Sleep Foundation: How many hours of sleep do you really need? (sleep need by age)
• Hilditch and McHill. Sleep inertia: current insights (2019) (waking from deep sleep and grogginess)