Free Sleep Calculator Built Around 90 Minute Cycles

Our Mission

Sleep deprivation is a global public health crisis. Public health bodies such as the US Centers for Disease Control and Prevention have described insufficient sleep as a public health problem. Yet the science of sleep timing is straightforward, evidence backed, and almost completely unknown to the public. BedtimeSleepCalculator.com exists to change that. We translate peer reviewed research into free, actionable tools anyone can use in 30 seconds.

The Science

Our calculator is grounded in the 1953 discovery by Nathaniel Kleitman and Eugene Aserinsky at the University of Chicago. They established that sleep progresses through 90 minute cycles of NREM and REM stages. Waking near the end of a cycle, rather than from deep sleep, tends to cause less grogginess. Cycle length varies, so the results are estimates. Our calculator finds your cycle aligned bedtime for any alarm time.

This information is for general sleep education only and is not medical advice. If you have ongoing sleep problems or a health condition, speak with a qualified healthcare professional.

Our Approach to Content

Our content is written and edited by F.A and checked against the sources listed below before publication. We do not claim medical review. For health decisions, talk to a doctor.

Research Sources

• Kleitman and Aserinsky (1953), Discovery of REM sleep and the 90 minute sleep cycle
• Van Dongen, Maislin, Mullington and Dinges (2003), Cumulative neurobehavioural effects of sleep restriction
• Walker (2017), Why We Sleep: Unlocking the Power of Sleep and Dreams
• National Sleep Foundation (Hirshkowitz et al., 2015), Updated sleep duration recommendations for all age groups

Editorial Independence

The site is funded by display advertising. Ads never decide what we write, and we do not accept sponsored content or paid placements that influence recommendations.