Sleep Calculator – Best Bedtime & Wake-up Times

Choose a mode, set a time, and we’ll suggest times that land at the end of 90-minute sleep cycles (we add a small buffer for falling asleep).

Set your time & options

Tip: People often feel best after 5–6 cycles (~7.5–9 hours). Your ideal may vary.
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How it works

Sleep tends to occur in ~90-minute cycles. Waking up at the end of a cycle can feel easier than waking mid-cycle. This calculator adds a short buffer (default 14 minutes) for the time it typically takes to fall asleep, then suggests bedtimes or wake-up times that land near the end of cycles.

FAQ

What assumptions does this calculator use?

We use 90-minute cycles and a default 14-minute fall-asleep buffer. You can change the buffer to suit you.

How many cycles should I target?

Many adults prefer 5–6 cycles (about 7.5–9 hours), but sleep need is individual. Use these times as gentle suggestions.

Is my data private?

Yes. Everything runs locally in your browser; no data is uploaded.

Additional Information About Sleep Cycles

Human sleep is divided into repeating 90-minute cycles, consisting of light sleep, deep sleep, and REM (rapid eye movement) sleep. Waking up at the end of a cycle generally feels easier than waking up in the middle of one.

Typical Sleep Needs

  • Adults: 7–9 hours (about 5–6 cycles)
  • Teenagers: 8–10 hours (about 5–7 cycles)
  • Children: 9–12 hours (about 6–8 cycles)
  • Infants: 12–16 hours including naps

Why Sleep Quality Matters

Sleep isn’t just about quantity—it’s also about quality. Factors like screen time, caffeine, stress, and environment (light, noise, temperature) affect how restorative your sleep cycles are. Good “sleep hygiene” practices, such as keeping a consistent bedtime and limiting blue light before bed, help improve quality.

Limitations of This Calculator

This tool provides general suggestions based on average cycle lengths. Everyone’s sleep architecture is unique, and cycles may range from 80–110 minutes. For ongoing sleep issues, consult a healthcare professional.

5 Fun Facts about Sleep Cycles

Your brain sets a timer

Right after you fall asleep your body releases adenosine and melatonin dips—part of why that first ~14-minute wind-down matters for timing cycles.

Wind-down window

Cycle length isn’t fixed

The “90 minutes” is an average—real cycles swing from 80–110 minutes. Early cycles pack more deep sleep; later ones tilt toward REM.

Varies by person

Light decides melatonin

Blue light nudges your internal clock later. Just 30–60 minutes of dim light before bed can make hitting cycle endpoints noticeably easier.

Light hygiene

REM stacks at the end

Most REM sleep clusters in the final cycles—skipping the last cycle can trim dreaming time even if total hours look okay.

Dream load

90 minutes isn’t magic

6 cycles at 90 minutes is 9 hours, but many people feel fine at 5 cycles (~7.5 hours) if their wake time is consistent.

Personal tuning

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