How many hours of sleep do I need?

Most adults need 7 to 9 hours of sleep per night according to the National Sleep Foundation 2022 guidelines. The optimal target for most people is 7.5 hours, which equals 5 complete 90-minute sleep cycles.

What is the best bedtime for a 7am alarm?

If your alarm is at 7am, the best bedtimes are 11:30pm (7.5 hours, 5 cycles) or 10pm (9 hours, 6 cycles). These are cycle-aligned times that let you wake at the end of a 90-minute sleep cycle.

About BedtimeCalc

Free Sleep Calculator Built Around 90 Minute Cycles

We built BedtimeSleepCalculator.com because sleep science is clear and the tools to apply it were not freely available. That changes when you understand 90 minute cycles.

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90 MinCycle Method

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Our Mission

Sleep deprivation is a global public health crisis. The WHO classifies insufficient sleep as an epidemic in industrialised nations. 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 at the end of a complete cycle produces dramatically less grogginess than waking mid cycle. Our calculator finds your cycle aligned bedtime for any alarm time.

Evidence standard: Every recommendation is grounded in peer reviewed research. We cite specific studies with author names, institutions, and publication years. We never make health claims that exceed what the evidence supports.

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 sleep education content is reviewed for clarity, accuracy, and general usefulness before publication.

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 (2022), Updated sleep duration recommendations for all age groups

Editorial Independence

We earn revenue through affiliate commissions on products in our sleep shop. These recommendations are chosen based on sleep science evidence, not payment. We do not accept sponsored content or paid placements that influence editorial recommendations.