Sleep Time / Bedtime Calculator
Plan your night around complete 90-minute sleep cycles so you wake feeling refreshed instead of groggy.
Mode
min
Head to bed at 21:45 — 6 full 90-minute cycles
- 1
Cycle duration
90Each sleep cycle lasts approximately 90 minutes. - 2
Total sleep (6 cycles)
6 × 90 = 540 - 3
Sleep hours
540 ÷ 60 = 9
How does this calculator work?
Sleep cycles run about 90 minutes, so aim to wake at the end of one. From your wake time, subtract whole cycles (4, 5, or 6 = 6, 7.5, or 9 hours) plus roughly 15 minutes to fall asleep to find ideal bedtimes; reverse the math from a fixed bedtime to find wake times.
Formula
How this is calculated
Sleep happens in repeating cycles of roughly 90 minutes that move from light sleep to deep sleep and REM. Waking at the end of a cycle, rather than in the middle of deep sleep, helps you feel alert, so this tool targets whole multiples of 90 minutes.
Enter the time you already know and your average minutes to fall asleep (about 15 for most people). In "wake time" mode the calculator subtracts cycles × 90 plus the fall-asleep buffer from your wake time to suggest bedtimes for 4, 5, and 6 cycles. In "bedtime" mode it adds the same amount to your bedtime to suggest wake times. Times use a 24-hour clock and wrap correctly across midnight.
Total sleep equals cycles × 90 minutes: 4 cycles is 6 hours, 5 is 7.5 hours, and 6 is the commonly recommended 9 hours. The 90-minute cycle and fall-asleep time are population averages; individual cycles range from about 70 to 120 minutes, so treat the suggestions as a guide and adjust to how you actually feel.
Frequently asked questions
A typical sleep cycle lasts about 90 minutes. Waking at the end of a cycle leaves you in lighter sleep, which usually feels far less groggy than waking mid-cycle during deep sleep.
Most adults do best with 5 to 6 cycles, which is about 7.5 to 9 hours of sleep. Four cycles (6 hours) can work occasionally but is short for sustained well-being.
You do not start sleeping the moment you lie down. Adding the minutes it takes to drift off (around 15 on average) makes the bedtime or wake-time estimate more realistic.
Also known as
TG we-Calculate Editorial Team. (2026). Sleep Time / Bedtime Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/sleep-time-calculator
TG we-Calculate Editorial Team. "Sleep Time / Bedtime Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/sleep-time-calculator.
TG we-Calculate Editorial Team, "Sleep Time / Bedtime Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/sleep-time-calculator
@misc{wecalculate_sleep_time_calculator, title = {Sleep Time / Bedtime Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/sleep-time-calculator}}, year = {2026}, note = {TG we-Calculate} }
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