Sleep / Bedtime Calculator
Find the best bedtime or wake-up time based on complete 90-minute sleep cycles, with an age-based recommended sleep range.
How to use the sleep calculator
- 1
Choose "I need to wake up at…" if you have a fixed alarm time, or "I'm going to bed at…" if you're heading to sleep now or at a set time.
- 2
Enter the time and select your age group so the calculator can highlight options in your recommended sleep range.
- 3
Pick a time from the results — each option completes a whole number of sleep cycles, with the closest match to a healthy 8 hours marked "Best fit." Open advanced settings to fine-tune your personal cycle length or how long you take to fall asleep.
How sleep cycles work
Rather than sleeping in one continuous block, your brain moves through repeating cycles of light sleep, deep sleep, and REM (rapid eye movement) sleep, each cycle averaging around 90 minutes. Early cycles in the night contain more deep sleep; later cycles shift toward more REM sleep, which is associated with dreaming and memory consolidation.
This calculator works backward or forward in whole 90-minute blocks (adjustable in advanced settings) so your target wake-up time lines up with the boundary between cycles, rather than landing in the middle of one. It also adds a default 15 minutes for the time it typically takes to fall asleep after getting into bed, since that time doesn't count toward an actual sleep cycle.
Cycle length genuinely varies by person and by night — some people run closer to 80 minutes, others closer to 100-120 — which is why the advanced settings let you adjust it rather than locking in a single fixed number.
Recommended sleep by age
| Age group | Recommended sleep |
|---|---|
| Newborn (0-3 months) | 14-17 hours |
| Infant (4-11 months) | 12-15 hours |
| Toddler (1-2 years) | 11-14 hours |
| Preschool (3-5 years) | 10-13 hours |
| School age (6-13 years) | 9-11 hours |
| Teen (14-17 years) | 8-10 hours |
| Adult (18-64 years) | 7-9 hours |
| Older adult (65+ years) | 7-8 hours |
Ranges reflect general National Sleep Foundation guidelines and aren't a substitute for medical advice — individual needs vary.
Tips for better sleep
Keep a consistent schedule: going to bed and waking up at similar times daily, even on weekends, helps your body settle into a predictable cycle rhythm rather than resetting it constantly.
Watch light exposure: bright light (including phone and laptop screens) late in the evening can delay when your body naturally starts producing sleep-promoting hormones, making it take longer to fall asleep than the 15-minute default this calculator assumes.
Give yourself a buffer: if you often take longer than 15 minutes to fall asleep, adjust the advanced setting so your bedtime accounts for it — otherwise your actual wake-up will land mid-cycle instead of at the boundary this calculator is aiming for.
Curious how sleep and energy connect to your daily calorie needs? Our Calorie Calculator (TDEE & BMR) estimates your daily energy needs based on activity level.
Tracking daily calories alongside your sleep schedule? Try the Calorie Calculator (TDEE & BMR) →