Sleep Calculator
Wake up feeling more rested by ending your sleep at the close of a cycle. Tell the calculator when you want to wake up — or when you're heading to bed — and it works out the best times using 90-minute sleep cycles, all in your browser with nothing uploaded.
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Pick a time to see your options.
How the sleep calculator works
Through the night your body cycles through light sleep, deep sleep, and REM in stretches of about 90 minutes. Waking at the end of a cycle — instead of being jolted out of deep sleep — is what makes the difference between groggy and refreshed.
Find your bedtime. Enter when you need to wake up. The calculator counts back in 90-minute cycles and adds the time it takes to fall asleep, then lists bedtimes that each land on a clean cycle boundary.
Find your wake-up time. Switch modes, enter your bedtime (or tap Use current time), and it counts forward to the wake times that fall at the end of a cycle.
Aim for the 5 or 6 cycle options — about 7.5 to 9 hours — which suit most adults. The shorter 3 and 4 cycle options are there for naps and short nights.
Everything runs in your browser — the times you enter are never uploaded.
Sleep calculator questions
How does it work? It counts in 90-minute cycles from your chosen time and adds time to fall asleep, so each suggestion ends at a cycle boundary.
How much sleep do I need? Most adults do best on 7–9 hours, roughly 5–6 cycles, which the tool marks as ideal.
Why 90 minutes? It's the common average length of one full cycle. Real cycles vary, so treat the times as targets, not exact science.
Going to bed now? Use go-to-bed mode with the current time to get suggested wake-up times.
Does it count the time to fall asleep? Yes — about 15 minutes by default, which you can change.
This is a general wellbeing aid, not medical advice. If you regularly struggle with sleep, talk to a doctor.