Sleep Calculator
Find ideal bedtimes or wake times based on 90-minute sleep cycles.
TL;DR — Sleep Calculator: A sleep calculator uses the 90-minute sleep cycle model to suggest bedtimes or wake times that align with the end of a cycle, when waking feels easiest. A full night is typically 5 or 6 cycles (7.5–9 hours), plus about 15 minutes to fall asleep. Choose to pick a wake time and see ideal bedtimes, or pick a bedtime and see ideal wake times.
What is the Sleep Calculator?
A sleep calculator uses the 90-minute sleep cycle model to suggest bedtimes or wake times that align with the end of a cycle, when waking feels easiest. A full night is typically 5 or 6 cycles (7.5–9 hours), plus about 15 minutes to fall asleep. Choose to pick a wake time and see ideal bedtimes, or pick a bedtime and see ideal wake times.
How to use the Sleep Calculator
- Choose a mode: pick a wake time, or pick a bedtime.
- Enter the chosen time.
- Read the recommended bedtimes (or wake times) for 4, 5 and 6 sleep cycles — the calculator adds 15 minutes for falling asleep.
Formula
Wake time = Bedtime + (15 min + 90 min × cycles) Bedtime = Wake time − (15 min + 90 min × cycles)
Standard sleep cycle ≈ 90 minutes. 5–6 cycles (7.5–9 hours) is typical for adults.
Worked example
You plan to wake at 7:00 am. To finish 6 cycles (9 h + 15 min) you should be in bed by 9:45 pm; 5 cycles by 11:15 pm; 4 cycles by 12:45 am.
Frequently asked questions
Why 90-minute cycles?
A sleep cycle moves through light, deep and REM stages over roughly 90 minutes. Waking at the end (light sleep) feels easier than mid-cycle.
How many cycles should I aim for?
5 or 6 cycles (7.5–9 hours) suits most adults. Teenagers need more; older adults may need slightly less.
Is the cycle exactly 90 minutes?
It varies between 70 and 120 minutes by person and across the night. 90 minutes is a good average.
What if I keep waking up tired?
Try going to bed 15 minutes earlier or later — you may be waking mid-cycle. Consistent sleep and wake times help too.
Does the calculator include time to fall asleep?
Yes. It adds 15 minutes between getting in bed and the first cycle starting.