How to use it
Choose a mode. Wake up at… works backwards from your alarm to show what time to go to bed. Go to sleep at… works forwards from when you'll fall asleep to show the best times to wake up — tap Set to now if you're heading to bed this minute. The results update live; there's no calculate button.
Each option ends at the close of a full 90-minute cycle, so your alarm is less likely to catch you in deep sleep. The rows for 5 and 6 cycles — roughly 7.5 to 9 hours — are highlighted because that's the sweet spot for most adults.
Sleep cycles & REM
A night's sleep isn't uniform. You move through light sleep, deep (slow-wave) sleep and REM sleep in cycles that average about 90 minutes. Deep sleep dominates early in the night; REM stretches get longer toward morning. Waking at the seam between cycles — in lighter sleep — feels gentler than being pulled out of deep sleep mid-cycle, which is where grogginess comes from.
How many hours of sleep by age
Sleep needs shift over a lifetime, so pick your age group to set the target the calculator highlights. The bands follow the National Sleep Foundation's evidence-based guidance for hours of sleep by age: kids 6–12 need about 9–11 hours, teens 13–17 about 8–10, adults 18–64 about 7–9, and older adults 65+ about 7–8. The cycle times themselves don't change with age — only which options are recommended for you.
The rest of your routine
Pair good sleep with easy training: find your heart rate zones, set eating targets with the TDEE Calculator, or plan a run with the Pace Calculator.
Cycles at a glance
| Cycles | Sleep | Feels like |
|---|---|---|
| 6 | 9 h | Full night |
| 5 | 7.5 h | Recommended (adult) |
| 4 | 6 h | Short but workable |
| 3 | 4.5 h | Get-through-it |
Highlighted rows show the adult target (7–9 h). Choose your age group in the calculator to shift the recommendation. Shorter nights are there for when life happens — not as a plan.
Recommended hours by age
| Age group | Hours / night |
|---|---|
| Kid (6–12) | 9–11 h |
| Teen (13–17) | 8–10 h |
| Adult (18–64) | 7–9 h |
| Older adult (65+) | 7–8 h |
Ranges per the National Sleep Foundation, reaffirmed in 2026. Set your age group in the calculator to highlight the cycle options that hit your target.
The 10-3-2-1 rule
| Before bed | Cut out |
|---|---|
| 10 hours | Caffeine |
| 3 hours | Food & alcohol |
| 2 hours | Work |
| 1 hour | Screens |
A simple wind-down checklist. It won't fix everything, but a consistent bedtime plus the highlighted cycle count does most of the work.
Common questions
How does the sleep calculator work?
Sleep runs in cycles of about 90 minutes, and waking at the end of a cycle rather than the middle tends to feel easier. The calculator counts back or forward in 90-minute blocks, adds roughly 15 minutes to fall asleep, and lists the times that land you at the end of a full cycle.
What time should I go to bed to wake at a set time?
Pick Wake up at…, enter your alarm time, and you'll get several bedtimes. Aim for one giving 5–6 cycles (7.5–9 hours) — those rows are highlighted.
How many sleep cycles do I need?
Most adults do best on 5–6 complete cycles a night, about 7.5–9 hours. Four cycles (6 hours) can work occasionally; three (4.5 hours) is a short night to get through, not a target.
Why 90 minutes and a 15-minute buffer?
A full cycle through light, deep and REM sleep averages about 90 minutes, though it varies. The extra 15 minutes covers the time most people take to actually fall asleep after lying down.
Does the ideal amount of sleep change with age?
The recommended nightly total does. Per the National Sleep Foundation: about 9–11 h for kids 6–12, 8–10 h for teens 13–17, 7–9 h for adults 18–64, and 7–8 h for older adults 65+. Set your age group and the highlighted rows update. The 90-minute cycle length doesn't meaningfully shift with adult age, so only the recommendation changes — not the times.
What is the 10-3-2-1 rule?
A wind-down guide: no caffeine 10 hours before bed, no food or alcohol 3 hours before, no work 2 hours before, no screens 1 hour before. A rule of thumb, not medical advice.