Sleep Calculator

Find the perfect bedtime or wake-up time based on 90-minute sleep cycles. Wake up feeling refreshed, not groggy.

Sleep Cycle Calculator

Average is 10–20 minutes for most adults
Best Times to Sleep
Best options are highlighted in green (6–9 hours). Each cycle is 90 minutes. Waking between cycles prevents sleep inertia (grogginess).

How Much Sleep Do You Need?

Newborn (0–3 mo)
14–17 hrs
Infant (4–11 mo)
12–15 hrs
Toddler (1–2 yr)
11–14 hrs
School Age (6–13)
9–11 hrs
Teen (14–17)
8–10 hrs
Adult (18–64)
7–9 hrs
Older Adult (65+)
7–8 hrs

Why Sleep Cycles Matter

A full sleep cycle lasts approximately 90 minutes and includes light sleep, deep sleep, and REM (rapid eye movement) sleep. Waking up in the middle of deep sleep — even after 8 hours — leaves you feeling groggy. Waking up at the end of a complete cycle feels natural and refreshed. This calculator aligns your bedtime or alarm to complete cycle boundaries.

The Science of Sleep Inertia

Sleep inertia is the groggy, disoriented feeling you get when woken abruptly from deep sleep. It can last 30–60 minutes and impairs cognitive performance significantly. Aligning your wake time to the end of a 90-minute cycle dramatically reduces sleep inertia, even if you technically slept fewer total hours.

The 14-Minute Offset

This calculator adds 14 minutes to your bedtime to account for the average time it takes adults to fall asleep (sleep onset latency). If you fall asleep faster or slower, adjust this field accordingly. Calculating from the moment you close your eyes — not when you actually sleep — is the most common mistake people make.