Sleep Calculator
Find the best time to go to bed or wake up by counting 90-minute sleep cycles, so you wake up at the end of a cycle, plus the hours of sleep needed at each age.
Adjust the calculation
| Newborns (0–3 months) | 14–17 hours |
| Infants (4–11 months) | 12–15 hours |
| Toddlers (1–2 years) | 11–14 hours |
| Preschoolers (3–5 years) | 10–13 hours |
| School-age children (6–13 years) | 9–11 hours |
| Teenagers (14–17 years) | 8–10 hours |
| Young adults (18–25 years) | 7–9 hours |
| Adults (26–64 years) | 7–9 hours |
| Older adults (65+ years) | 7–8 hours |
What it does
During the night sleep goes through cycles of about 90 minutes, from light sleep to deep sleep and REM, the stage of dreams. Waking up at the end of a cycle, in light sleep, is easier than in the middle of deep sleep. This calculator counts whole cycles back from the time you want to wake up, or forward from the time you go to bed, and adds the time you take to fall asleep. Five or six cycles give the 7 to 9 hours recommended for adults.
How to use it
- Choose whether you know the time you want to wake up or the time you are going to bed.
- Enter the time, or press now to go to bed right away.
- Pick one of the times shown; the recommended ones give 7 to 9 hours of sleep.
The arithmetic runs in your browser. Nothing you type is sent anywhere and nothing is stored, so you can use these with real numbers.
Frequently asked questions
Why 90-minute cycles?
A night of sleep usually has four to six cycles that last about 90 minutes each, although they can range from 70 to 120 minutes. If you know your cycles are shorter or longer, you can change the length in the settings.
Why are 15 minutes added?
Most people take 10 to 20 minutes to fall asleep. If you fall asleep faster or slower, change that time in the settings and the times are recalculated.
How many hours of sleep do I need?
Adults need 7 to 9 hours, teenagers 8 to 10 and school-age children 9 to 11, according to the National Sleep Foundation; the table above shows every age group. Going to bed and waking up at regular times matters as much as the total.
⏱️ Time Calculator
🍅 Pomodoro Timer
National Sleep Foundation — How many hours of sleep do you need?
Wikipedia — Sleep cycle