Life Tools

Sleep Calculator

Find the best time to wake up or go to sleep. Based on 90-minute sleep cycles, wake at the end of one and you'll feel alert instead of groggy.

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What do you want to find?

I want to wake up at

~14 min to fall asleep is factored in

Each sleep cycle = 90 min · 5–6 cycles is ideal for adults

Go to sleep at

02:16 AM

4.5h · 3 cycles

Min

12:46 AM

6h · 4 cycles

Good

11:16 PM

7.5h · 5 cycles

Ideal

09:46 PM

9h · 6 cycles

Ideal

If you need to wake up at 07:00 AM, go to bed at one of the times above

If you fall asleep right now, wake up at

01:18 PM

4.5h · 3 cycles

Min

02:48 PM

6h · 4 cycles

Good

04:18 PM

7.5h · 5 cycles

Ideal

05:48 PM

9h · 6 cycles

Ideal

Recommended sleep by age (National Sleep Foundation)

Age group	Age range	Hours/night	Sleep cycles
Newborn	0–3 months	14–17h	9–11
Infant	4–11 months	12–15h	8–10
Toddler	1–2 years	11–14h	7–9
Preschool	3–5 years	10–13h	7–9
School-age	6–13 years	9–11h	6–7
Teen	14–17 years	8–10h	5–7
Young adult	18–25 years	7–9h	5–6
Adult	26–64 years	7–9h	5–6
Older adult	65+ years	7–8h	5

How to use the sleep calculator

Two inputs, four results. Pick the time that fits your schedule and lands at the end of a cycle.

01
Choose your mode
Pick 'I want to wake up at…' to find the best bedtime, or 'I'm going to bed at…' to find the best alarm time. Both work the same way, just in opposite directions.
02
Enter your time
Type in your target wake-up or bed time. The calculator adds ~14 minutes (average time to fall asleep) before counting your 90-minute cycles.
03
Pick a wake-up or sleep time from the results
You'll see four options: 4.5h, 6h, 7.5h, and 9h of sleep. For most adults, 5–6 cycles (7.5h–9h) is ideal. The 'Sleep right now' section shows options if you're going to bed immediately.

When people use this

Setting a smarter alarm

Instead of setting your alarm for exactly 8 hours, pick the nearest cycle boundary. Waking at 7h 30min often feels better than waking at 8h flat.

Adjusting for an early meeting

Have a 6 AM call? Work backwards from 6:00 to find a bedtime that lands at the end of a cycle, 10:06 PM or 11:36 PM rather than an arbitrary 10:00 PM.

Recovering from a late night

If you went to bed at 2 AM, use the 'going to bed at' mode to find the best wake-up times. Sleeping until 7:44 AM (3.5 cycles) beats sleeping until 8:00 AM mid-cycle.

Planning naps

A 20-minute nap avoids deep sleep entirely. A 90-minute nap completes one full cycle. Anything in between (30–80 minutes) tends to leave you groggy.

How the times are worked out

The calculator assumes it takes you about 14 minutes to fall asleep and that sleep runs in cycles of about 90 minutes. To wake at 6:30 am at the end of a cycle, it counts back whole cycles plus the 14 minutes.

Cycles	Sleep time	Go to bed by (to wake at 6:30 am)
6	9 hours	9:16 pm
5	7.5 hours	10:46 pm
4	6 hours	12:16 am

Going the other way, if you're in bed at 11:00 pm, waking after 4, 5 or 6 cycles means 5:14, 6:44 or 8:14 am. For most adults, 5 cycles is the practical target: it lands inside the 7 to 9 hours recommended for ages 18 to 64.

Why the times are a guide, not a rule

Real sleep cycles vary from roughly 70 to 120 minutes, and they change through the night, with more deep sleep early and more REM sleep later. A 90-minute cycle is an average.
Falling asleep can take much longer than 14 minutes after caffeine, screens or stress, which shifts every wake time.
Consistency matters more than precise timing. Going to bed and getting up at the same time every day, weekends included, helps more than hitting an exact cycle.
If you regularly sleep the recommended hours and still feel unrefreshed, or snore heavily, talk to a doctor about sleep apnoea or other sleep disorders.

Frequently asked questions

Free, no account needed. Everything runs in your browser.

The 14-minute offset is an average. If you know you fall asleep in 5 minutes or 30 minutes, mentally adjust the suggested times by that difference.

Most adults need 7–9 hours (5–6 cycles). Consistently sleeping fewer than 6 hours is linked to impaired cognition, weakened immunity, and higher cardiovascular risk.

Yes. Just enter your actual planned sleep or wake time. The cycle math is the same regardless of whether you sleep at night or during the day.

Nothing is sent to any server. The calculation runs entirely in your browser.

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