Sleep Calculator
Best bedtimes and wake times by sleep cycle.
Enter your values
Enter the wake-up time in HH:MM.
Enter the minutes to fall asleep you are working with.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 6 cycles (9 hrs)
- Sleep at 21:15
- 5 cycles (7.5 hrs)
- Sleep at 22:45
- 4 cycles (6 hrs)
- Sleep at 00:15
- Recommended for adults
- 5–6 cycles, 7.5–9 hours
- Falling-asleep buffer
- 15 minutes
Quick answer
Sleep runs in roughly 90-minute cycles, so waking at a multiple of 90 minutes after falling asleep feels far less groggy.
At a glance
| What it does | Best bedtimes and wake times by sleep cycle. |
|---|---|
| Category | Health |
| Inputs needed | Wake-up time, Minutes to fall asleep |
| Main output | 6 cycles (9 hrs) |
| Cost | Free — no sign-up, no download |
How to use the Sleep Calculator
- 1Enter the time you must wake up.
- 2Set how long you usually take to fall asleep.
- 3Pick one of the suggested bedtimes.
Inputs explained
- Wake-up time(HH:MM)
- Enter the wake-up time in HH:MM.
- Minutes to fall asleep
- Enter the minutes to fall asleep you are working with.
Worked example
Using the values the calculator loads with:
Inputs
- Wake-up time06:30 HH:MM
- Minutes to fall asleep15
Results
- 6 cycles (9 hrs)Sleep at 21:15
- 5 cycles (7.5 hrs)Sleep at 22:45
- 4 cycles (6 hrs)Sleep at 00:15
- Recommended for adults5–6 cycles, 7.5–9 hours
- Falling-asleep buffer15 minutes
Frequently asked questions
Why 90 minutes?
A full cycle through light, deep and REM sleep averages 90 minutes. Waking mid-deep-sleep causes grogginess.
Is 6 hours enough?
For most adults no — four cycles is a minimum for a short night, but 7–9 hours is the healthy range.
What do I need to enter into the Sleep Calculator?
Just 2 values: wake-up time, minutes to fall asleep. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Sleep Calculator work out the answer?
Sleep runs in roughly 90-minute cycles, so waking at a multiple of 90 minutes after falling asleep feels far less groggy. The working is shown step by step so you can verify the result by hand.
Is the Sleep Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.