Sleep Calculator
Wake up refreshed, not groggy. Based on 90-minute sleep cycles, this works out the best times to go to bed — or to set your alarm — so you wake between cycles. Instant, on your device.
Go to bed at one of these:
- 9:45 pm9 hrs sleepbest
- 11:15 pm7.5 hrs sleepbest
- 12:45 am6 hrs sleep
- 2:15 am4.5 hrs sleep
Allowing about 15 minutes to fall asleep. Aim for 5–6 cycles (7.5–9 hours) most nights.
Sleep cycles are roughly 90 minutes but vary from person to person and night to night, so treat these as a helpful guide. Ongoing sleep problems are worth raising with your GP.
How sleep cycles affect waking up
You sleep in cycles of roughly 90 minutes, moving from light sleep into deep sleep and back. Waking up at the end of a cycle — in lighter sleep — tends to feel far easier than being dragged awake from deep sleep, which is that groggy, heavy feeling. This calculator counts in 90-minute cycles so you can aim to wake between them.
Tell it when you need to wake up and it suggests the best bedtimes; or tell it when you're going to sleep and it suggests when to set your alarm. It allows about 15 minutes to fall asleep, and highlights 5–6 cycles (7.5–9 hours) as the sweet spot for most adults. Everything runs on your device with nothing saved.
Frequently asked questions
What time should I go to bed to wake up at 7am?⌄
Enter 7am in 'wake up' mode and the calculator counts back in 90-minute cycles — typically suggesting bedtimes around 9:45pm, 11:15pm or 12:45am, allowing time to fall asleep.
How many hours of sleep do I need?⌄
Most adults do best on 7–9 hours, which is about 5–6 sleep cycles. The calculator highlights those options as the recommended ones.
Why do I wake up groggy even after lots of sleep?⌄
Often it's because your alarm went off in the middle of a deep-sleep stage. Waking at the end of a cycle, in lighter sleep, usually feels more refreshing — which is what this tool aims for.
Are sleep cycles exactly 90 minutes?⌄
No — 90 minutes is an average. Cycles vary between people and across the night, so treat the times as a helpful guide rather than a precise rule.
Should I see a doctor about my sleep?⌄
If you regularly struggle to fall asleep, stay asleep, or feel exhausted despite enough hours, it's worth speaking to your GP.