😴 Sleep Cycle Calculator

The best bedtimes and wake times based on 90-minute sleep cycles

Best Bedtimes

Each cycle ≈ 90 minutes, plus ~15 minutes to fall asleep. Waking at the end of a cycle (light sleep) feels dramatically better than mid-cycle (deep sleep). Adults need 5–6 cycles (7.5–9 hours).

How Sleep Cycles Work

Sleep runs in ~90-minute cycles through light sleep, deep sleep and REM. Waking mid-deep-sleep causes grogginess (sleep inertia) that can last an hour; waking between cycles — in light sleep — feels natural and alert. Timing beats raw duration for how you feel.

How Much Sleep Do Adults Need?

The NHS recommends 7–9 hours for adults — that’s 5–6 full cycles. Consistency matters as much as quantity: the same bedtime and wake time daily (weekends included) trains your circadian rhythm.

Falling Asleep Faster

  • No screens 30–60 minutes before bed (blue light suppresses melatonin)
  • Cool room — 16–18°C is optimal
  • Caffeine has a 6-hour half-life — last coffee before 2pm
  • Consistent wind-down routine signals sleep to your brain

Frequently Asked Questions

What time should I go to bed to wake at 7am?

Working back in 90-minute cycles plus 15 minutes to fall asleep: 9:45pm for 6 cycles (ideal) or 11:15pm for 5 cycles.

Why do I feel groggy after 8 hours of sleep?

You likely woke mid-cycle during deep sleep. Waking at a cycle boundary in light sleep feels far better even with slightly less total sleep.

How long is one sleep cycle?

About 90 minutes, moving through light sleep, deep sleep and REM. Adults need 5–6 complete cycles a night.