# Sleep Calculator

> To wake up at 7:00 AM after five or six full 90-minute sleep cycles, go to bed at 11:15 PM or 9:45 PM, allowing 15 minutes to fall asleep. Enter a wake-up time or bedtime to get times that line up with whole sleep cycles, and check how much sleep is recommended for your age.

- Interactive calculator: https://calculatorswithsteps.com/sleep-calculator
- Category: Health & Fitness Calculators
- Last updated: 2026-11-10
- Publisher: Calculators With Steps (calculatorswithsteps.com)

## How to use the sleep calculator

1. Choose **Wake-up time** to find when to go to bed, **Bedtime** to find when to set your alarm, or **Sleep now** to count from the current time.
2. Enter the time. The calculator handles times that cross midnight.
3. Adjust **time to fall asleep** if you usually take more or less than 15 minutes, and **cycle length** if you know your cycles run shorter or longer than 90 minutes.

The result shows two recommended times, usually for 5 and 6 cycles, plus a table of every option from 3 cycles up and the CDC's recommended sleep by age.

## How sleep cycles are calculated

During the night you move through light sleep (N1 and N2), deep sleep (N3) and REM sleep, then start again. The NHLBI describes each cycle as restarting every 80 to 100 minutes, with four to six cycles a night. The calculator uses 90 minutes as a round average.

**Bedtime = wake-up time − (number of cycles × cycle length) − time to fall asleep**

**Wake-up time = bedtime + time to fall asleep + (number of cycles × cycle length)**

For example, to wake at 7:00 AM after 5 cycles: 5 × 90 = 450 minutes, or 7 hours 30 minutes. 7:00 AM minus 7 h 30 min is 11:30 PM, and minus another 15 minutes to fall asleep is **11:15 PM**. For 6 cycles (9 hours) the bedtime is **9:45 PM**.

## Bedtimes for common wake-up times

All times assume 90-minute cycles and 15 minutes to fall asleep.

| Wake-up time | Bedtime for 6 cycles (9 h) | Bedtime for 5 cycles (7 h 30 min) | Bedtime for 4 cycles (6 h) |
| --- | --- | --- | --- |
| 5:30 AM | 8:15 PM | 9:45 PM | 11:15 PM |
| 6:00 AM | 8:45 PM | 10:15 PM | 11:45 PM |
| 6:30 AM | 9:15 PM | 10:45 PM | 12:15 AM |
| 7:00 AM | 9:45 PM | 11:15 PM | 12:45 AM |
| 7:30 AM | 10:15 PM | 11:45 PM | 1:15 AM |
| 8:00 AM | 10:45 PM | 12:15 AM | 1:45 AM |

Going the other way, a 10:30 PM bedtime gives wake-up times of 6:15 AM (5 cycles) or 7:45 AM (6 cycles), and an 11:00 PM bedtime gives 6:45 AM or 8:15 AM.

## How much sleep you need by age

| Age group | Age | Recommended sleep per 24 hours |
| --- | --- | --- |
| Newborn | 0–3 months | 14–17 hours |
| Infant | 4–12 months | 12–16 hours, including naps |
| Toddler | 1–2 years | 11–14 hours, including naps |
| Preschool | 3–5 years | 10–13 hours, including naps |
| School age | 6–12 years | 9–12 hours |
| Teen | 13–17 years | 8–10 hours |
| Adult | 18–60 years | 7 or more hours |
| Adult | 61–64 years | 7–9 hours |
| Older adult | 65+ years | 7–8 hours |

The CDC table draws on consensus statements from the American Academy of Sleep Medicine and the National Sleep Foundation. For adults, 5 cycles (7.5 hours) or 6 cycles (9 hours) both meet the 7-hour minimum.

## What the evidence says about sleep cycles

The idea behind the calculator is reasonable: waking from light sleep near the end of a cycle usually feels easier than being pulled out of deep sleep, when grogginess (sleep inertia) is stronger. But treat the times as a guide, not a precise schedule:

- **Cycles vary.** Sleep Foundation notes that the first cycle often lasts 70 to 100 minutes and later cycles 90 to 120 minutes. Over 5 or 6 cycles, those differences add up to half an hour or more.
- **Cycles change through the night.** Deep sleep is concentrated early in the night and REM sleep gets longer toward morning.
- **Total sleep matters most.** Getting enough hours on a regular schedule does more for health than hitting an exact cycle boundary.

If your times do not feel right, change the cycle length by 5 to 10 minutes or adjust the time you allow to fall asleep, then try it for a week.

## Tips for better sleep

- Keep the same wake-up time every day, including weekends.
- Use the bedtime from the calculator as your lights-out target, and start winding down 30 to 60 minutes before.
- For a short daytime nap, 20 minutes or less avoids deep sleep. A full 90-minute cycle is the other option when you have time.
- Regular exercise helps sleep, though hard sessions close to bedtime can keep some people awake. The [target heart rate calculator](https://calculatorswithsteps.com/target-heart-rate-calculator) helps you keep evening workouts easy.
- To total up hours slept across a week, the [hours calculator](https://calculatorswithsteps.com/hours-calculator) does the arithmetic.

## Frequently asked questions

### How does a sleep calculator work?

It counts in whole sleep cycles of about 90 minutes and adds the time it takes you to fall asleep. Waking at 7:00 AM after 6 cycles (9 hours) means being asleep by 10:00 PM, so with 15 minutes to drift off you should be in bed by 9:45 PM.

### What time should I go to bed if I wake up at 6 AM?

Go to bed at 8:45 PM for 6 cycles (9 hours of sleep) or 10:15 PM for 5 cycles (7.5 hours), assuming 15 minutes to fall asleep. If you need to stretch it, 11:45 PM gives 4 cycles, or 6 hours, which is less than most adults need.

### What time should I wake up if I go to bed at 10:30 PM?

Aim for 6:15 AM after 5 cycles or 7:45 AM after 6 cycles. Both assume you fall asleep by 10:45 PM and sleep in 90-minute cycles.

### How long is a sleep cycle?

About 90 minutes on average. The NHLBI says a cycle restarts every 80 to 100 minutes and most people have 4 to 6 cycles a night. The first cycle is often shorter, from about 70 to 100 minutes, and later ones can run 90 to 120 minutes.

### How many hours of sleep do I need?

The CDC recommends 7 or more hours for adults aged 18 to 60, 7 to 9 hours at 61 to 64, and 7 to 8 hours from 65. Teens aged 13 to 17 need 8 to 10 hours and children aged 6 to 12 need 9 to 12 hours.

### Is 6 hours of sleep enough?

Not for most adults. Six hours is 4 full cycles and falls short of the 7-hour minimum the CDC recommends for adults. A few people do well on less, but regularly sleeping under 7 hours is linked with health problems.

### How do I calculate sleep efficiency?

Divide the time you were actually asleep by the time you spent in bed and multiply by 100. If you were in bed for 8 hours and asleep for 7 hours, your sleep efficiency is 7 ÷ 8 × 100 = 87.5%.

### What is sleep debt?

Sleep debt is the gap between the sleep you need and the sleep you get. If you need 7.5 hours and sleep 6 hours on five work nights, you build up 7.5 hours of sleep debt over the week.

## Sources

- [CDC – About Sleep (recommended hours by age)](https://www.cdc.gov/sleep/about/index.html)
- [NHLBI – Sleep Phases and Stages](https://www.nhlbi.nih.gov/health/sleep/stages-of-sleep)
- [Sleep Foundation – Stages of Sleep](https://www.sleepfoundation.org/how-sleep-works/stages-of-sleep)

> Disclaimer: results are estimates for information and education, not medical advice. Confirm important decisions with a qualified professional.