Sleep Calculator: Best Bedtime and Wake-Up Time
Choose whether you know your wake-up time or bedtime, enter it, and see times that fit whole 90-minute sleep cycles.
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Formula
Time in bed = cycles × 90 minutes + minutes to fall asleep
Bedtime is the wake-up time minus this; wake-up time is the bedtime plus this.
Worked example
Wake at 07:00 with 15 minutes to fall asleep: 5 cycles = 450 + 15 = 465 minutes (7 h 45 min), so go to bed at 23:15. Six cycles gives 21:45.
Frequently asked questions
How does the sleep calculator work?
Sleep runs in cycles of about 90 minutes. The calculator adds or subtracts whole cycles plus the time you take to fall asleep. Waking at 07:00 with 15 minutes to fall asleep, 5 cycles means going to bed at 23:15.
How many sleep cycles do I need?
Most adults do well with 5 or 6 cycles, which is 7.5 to 9 hours. Individual needs differ.
Why include time to fall asleep?
Cycles start when you actually fall asleep, not when you lie down. If it takes 15 minutes, a 7 h 30 min sleep needs 7 h 45 min in bed.
Are 90-minute cycles exact?
No. Cycle length varies between people and through the night, usually between 80 and 110 minutes. Treat the times as a guide, not a guarantee.