Sleep Calculator
Wake up refreshed by ending sleep at the end of a complete 90-minute cycle. Pick a target wake-up time and see the best bedtimes, or pick a bedtime and see the best wake-up times. Adjustable for how long you take to fall asleep.
All calculations run in your browser. Nothing is uploaded.
This calculator is for informational use only and is not medical advice. Individual cycle length varies (80-120 minutes is normal). For persistent sleep problems, consult a healthcare professional.
How to use this sleep calculator
- Pick a mode: 'Wake up at...' if you have an alarm time, or 'Go to bed at...' if you're heading to bed.
- Enter the target time, or tap 'Now' if going to bed immediately.
- Adjust the 'time to fall asleep' if 14 minutes doesn't match you (typical range 5-30 min).
- Pick a result card — 6 cycles (9h) is optimal, 5 cycles (7.5h) is great, 4 cycles (6h) is the minimum for most adults.
Frequently asked questions
Why 90 minutes per cycle?
One full sleep cycle is roughly 90 minutes and moves through light sleep, deep sleep and REM. Waking at the end of a cycle (in light sleep) feels much easier than waking in deep sleep, which is why 90 minutes is the standard reference used by sleep researchers.
What are REM sleep cycles?
REM (rapid eye movement) sleep is the stage where dreams happen and memory consolidates. Each ~90-minute cycle ends with a REM phase, and ending sleep right after REM (not in deep sleep) leaves you feeling rested.
Why does the calculator add 14 minutes?
On average, healthy adults take about 10-20 minutes to actually fall asleep after lying down — this is called sleep latency. We add 14 minutes by default so the cycles count from when you're actually asleep, not when you got into bed. You can adjust this if you fall asleep faster or slower.
Who is this calculator for?
Anyone planning around sleep: students with early classes, shift workers, parents, travellers crossing time zones, or anyone who wants to wake up less groggy. It's not a substitute for treatment of insomnia or sleep disorders — see a doctor for those.