Sleep Calculator

The Sleep Calculator helps you time your sleep around natural 90-minute sleep cycles. Tell it when you need to wake up and it suggests bedtimes, or tell it when you're going to bed and it suggests wake-up times — so your alarm lands between cycles instead of in the middle of deep sleep, and you wake up feeling less groggy.

How to use the Sleep Calculator

1. Choose “I want to wake up at” or “I'm going to bed at”.
2. Enter the time, or tap “Going to bed now” to start from the current time.
3. Read the suggested times — 5 cycles (7.5 hours) is highlighted as a good target for most adults.
4. Set your alarm or head to bed at the time that fits your schedule.

Frequently asked questions

How does the sleep calculator work?

Sleep runs in cycles of about 90 minutes. The calculator adds about 15 minutes to fall asleep, then counts whole cycles forward from your bedtime or backward from your wake-up time, so you wake at the end of a cycle.

Why do I feel groggy even after enough sleep?

Waking up in the middle of deep sleep causes sleep inertia — that heavy, foggy feeling. Waking near the end of a cycle, when sleep is lighter, usually feels much easier, even if the total time is slightly shorter.

How many sleep cycles do I need?

Most adults need 7–9 hours a night, which is about 5 to 6 cycles. Four cycles (6 hours) can work occasionally, but regularly sleeping that little adds up to sleep debt.

Are sleep cycles exactly 90 minutes?

Not exactly — cycles typically range from about 80 to 110 minutes and vary from night to night. Treat the times as a helpful guide and adjust by 10–15 minutes if you notice you wake more easily at a slightly different time.