TopToolsAiFind the best bedtimes to hit a full number of 90-minute sleep cycles before your desired wake-up time, so you wake up between cycles instead of mid-cycle feeling groggy. Working backward from a 6:30am wake-up in 90-minute cycles gives bedtimes of 9:00pm (5 cycles), 10:30pm (4 cycles) or midnight (3 cycles) — falling asleep isn't instant, so the tool builds in roughly 15 minutes to actually drift off.
Last updated: 1 Sep 2026
How to use Sleep Time Calculator
- Enter the time you want to wake up.
- Click "Suggest bedtimes".
- You'll get several bedtime options, each based on complete 90-minute sleep cycles.
Frequently asked questions
Why 90-minute cycles specifically?
A full sleep cycle (light sleep, deep sleep, REM) averages about 90 minutes for most adults. Waking up at the end of a cycle rather than mid-cycle tends to feel less groggy.
How many cycles do I actually need?
Most healthy adults need 5-6 cycles (7.5-9 hours) per night for full recovery, though this varies by individual.
Should I use "wake up at" or "go to sleep at" mode?
Use "wake up at" if you have a fixed alarm time and want to know when to go to bed; use "go to sleep at" if you're heading to bed now and want to know the best wake times.
Does it account for the time it takes to fall asleep?
Yes, it typically factors in a short buffer (commonly ~15 minutes) for falling asleep before the first cycle begins.
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