Sleep Calculator

Best bedtimes & wake times by sleep cycle.

Work out the best time to go to bed or wake up so your alarm lands at the end of a 90-minute sleep cycle — the trick to waking up refreshed instead of groggy. Enter a wake-up time or a bedtime and get cycle-aligned suggestions, allowing time to fall asleep. Runs fully in your browser — nothing is uploaded.

Sleep Calculator features

How to use Sleep Calculator

  1. Choose your mode

    Pick whether you know your wake-up time or your bedtime — the calculator works both ways.

  2. Enter the time

    Set the time you must wake up, or the time you're heading to bed; tap 'Use now' to start from the current moment.

  3. See the ideal times

    The tool lists times that fall at the end of complete 90-minute sleep cycles, allowing ~15 minutes to drift off.

  4. Pick a starred option

    Aim for a ⭐ option (5–6 cycles, 7.5–9 hours) for a full night that ends on a light-sleep phase.

  5. Wake up refreshed

    Waking at the end of a cycle avoids the grogginess of being pulled out of deep sleep.

Frequently asked questions

How does the sleep cycle calculator work?

It counts backward or forward in 90-minute blocks — the length of one sleep cycle — and adds about 15 minutes to fall asleep. Times that land at the end of a full cycle are when you'll wake most easily.

How many hours of sleep do I need?

Most adults need 7–9 hours, which is 5–6 complete cycles. Teens need a little more. The starred options in the results (7.5 and 9 hours) hit that sweet spot.

Why do I wake up groggy even after 8 hours?

You were probably pulled out of deep sleep mid-cycle. Aligning your alarm to the end of a cycle — as this tool suggests — usually leaves you feeling more refreshed even with the same total sleep.

Is 6 hours of sleep enough?

Six hours is four cycles — okay occasionally, but below the 7–9 hours most adults need for full recovery. Use it only when you can't get a longer night, and try to catch up afterward.

What time should I go to bed to wake up at 6 am?

Working back in 90-minute cycles from 6 am (plus ~15 minutes to fall asleep), good bedtimes are around 8:45 pm, 10:15 pm or 11:45 pm — the end of a full cycle. Enter 6 am as your wake time here and the calculator lists the exact options.

Is it better to wake at the end of a sleep cycle?

Yes. Waking at the end of a 90-minute cycle, in light sleep, usually leaves you feeling more refreshed than being jolted out of deep sleep mid-cycle — even with the same total hours. That's what this calculator's suggested times aim for.

Is my data stored?

No. The times are computed entirely in your browser; nothing is uploaded.

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