Sleep Calculator
Get ideal bedtimes or wake-up times based on natural ~90-minute sleep cycles. Enter a wake-up time or a bedtime and see options that help you wake between cycles — feeling more refreshed.
How this Sleep Calculator works
Your sleep follows ~90-minute cycles. Waking between cycles usually feels better than waking mid-cycle. This calculator assumes:
- Sleep cycle length: 90 minutes (typical average)
- Sleep onset: we implicitly add ~15 minutes to fall asleep (no input needed)
If you set a wake-up time, we suggest bedtimes by subtracting onset + 4-6 cycles. If you set a bedtime, we suggest wake-up times by adding onset + 4-6 cycles.
Why this calculator is important for your health
Sleep cycles — the basics
A sleep cycle is the repeated shift between non-REM and REM sleep. Through the night, your brain moves through these two types of sleep in a predictable pattern.
Circadian clock & timing
Your sleep timing is guided by the body's circadian clock—a hormonal rhythm synced to light and darkness. When external cues change abruptly (e.g., long-haul flights), your internal clock can fall out of sync (jet lag), so you feel sleepy or alert at the “wrong” local time.
Light exposure, work schedules, social life, naps, and genetics can all nudge this timing.
REM vs non-REM — what's the difference?
- Non-REM: Brain activity and energy use drop, especially in deep slow-wave sleep. Heart rate and body temperature fall, tissues repair, and the brain replenishes energy stores (like ATP). Growth hormone is primarily released during this phase.
- REM: Features rapid eye movements, temporary muscle paralysis, and vivid dreaming. REM usually makes up a smaller slice of total sleep time and alternates with non-REM.
How the night unfolds
Across a typical night, the body cycles through non-REM and REM roughly every ~90 minutes, repeating 4-6 times. Non-REM starts the cycle, often progressing into deep slow-wave sleep before transitioning to REM. Good sleep means smooth transitions between these stages.
Why REM matters (and what happens if you miss it)
Lack of REM can lead to irritability, anxiety, trouble concentrating, and even hallucinations in extreme cases. After REM loss, the body often “rebounds,” trying to enter REM more often and for longer. Scientists still debate some functions of REM, but most agree it's important—even though short-term REM reduction can sometimes have temporary, specific effects.
Sleep quality — how to think about it
Quality sleep means: (1) falling asleep without much difficulty, (2) staying asleep with few awakenings, and (3) waking up feeling restored. To improve quality, align sleep timing with your circadian rhythm. Aim for your melatonin peak and lowest core body temperature to occur mid-sleep rather than right before waking.
How much sleep do you need?
Needs vary by person and age. Many adults feel and function best around 7-9 hours, but individual differences are real. The key signal of “enough” is no daytime sleepiness or impairment.
CDC recommended sleep durations by age
Recommended Hours of Sleep by Age
| Age Group | Recommended Hours of Sleep Per Day |
|---|---|
| 0-3 months | 14-17 hours |
| 4-12 months | 12-16 per 24 hours (incl. naps) |
| 1-2 years | 11-14 per 24 hours (incl. naps) |
| 3-5 years | 10-13 per 24 hours (incl. naps) |
| 6-12 years | 9-12 per 24 hours |
| 13-18 years | 8-10 per 24 hours |
| 18-60 years | 7 or more per night |
| 61-64 years | 7-9 |
| 65 years and older | 7-8 |
Tips
- Pick your wake-up time first, then back-calculate 4-6 full cycles (≈90 min each) plus your sleep-onset time (typically 10-20 min).
- Keep a steady schedule. Aim to go to bed and wake up within a ±30-60 min window, even on weekends.
- Dim light and screens 60-90 minutes before bed; reduce blue light and notifications.
- Mind stimulants. Limit caffeine after noon and avoid heavy meals 2-3 hours before bed; alcohol can fragment sleep.
- Nap smart. Keep power naps to 10-20 minutes. If you need longer, target ~90 minutes (one full cycle).
- Get morning light. Natural light soon after waking helps anchor your circadian rhythm.
- Optimize your bedroom. Cool, dark, quiet environment (roughly 18-20°C/64-68°F) supports deeper sleep.
- Place your alarm out of reach. Snoozing repeatedly increases sleep inertia.
Common mistakes
- Counting time in bed as sleep. Ignoring sleep latency skews the plan.
- Waking mid-cycle. Picking arbitrary times that cut through a 90-minute cycle increases grogginess.
- Chasing “perfect” minutes. Cycles vary by ~10-20 minutes—treat outputs as windows, not exact timestamps.
- Weekend drift (“social jet lag”). Shifting schedule by 2+ hours makes Monday harder.
- Late caffeine or alcohol. Both can suppress deep sleep or REM and fragment the night.
- Bright screens in bed. Blue light and doom-scrolling delay sleep onset.
- Long, late naps. Napping close to bedtime or for 60-90 minutes can delay nighttime sleep.
- Assuming everyone has 90-min cycles exactly. It's an average—adjust to how you actually feel on waking.
- Ignoring persistent problems. If poor sleep continues, consider discussing it with a healthcare professional.