Sleep Cycle Calculator

During sleep, light (REM) and deep (non-REM) sleep alternate in cycles of roughly 90 minutes. If your alarm rings during deep sleep you tend to feel groggy, while waking at a cycle boundary (light sleep) makes it easier to feel refreshed. This tool calculates the best bedtime or wake-up time from that rhythm.

How to use this tool

Enter your wake-up time and you get bedtime options for 4–6 cycles (6, 7.5 and 9 hours of sleep). Or, going to bed now? Enter your bedtime and get the best times to wake. Both include an average 15 minutes to fall asleep.

Sleep and strength training

Growth hormone — key to muscle repair — is secreted most during the deep non-REM sleep just after falling asleep. Sleep deprivation lowers testosterone, disrupts appetite and hurts training quality, which is why sleep is often called the third pillar of training (exercise, nutrition, rest). 7–9 hours is the common recommendation.

Tips

Keeping consistent bed and wake times stabilizes your cycles and improves mornings. Recovery also needs nutrition — check daily calories with the TDEE Calculator and protein with the Protein Calculator.

The 90-minute cycle is an average

Sleep cycles are usually quoted at "about 90 minutes", but in reality they range from roughly 80 to 110 minutes and vary within a single night. Deep non-REM sleep dominates the early hours, while REM takes a larger share towards morning and cycles tend to lengthen. Timing a wake-up to a multiple of 90 minutes is a reasonable heuristic, but it is not something that can be optimised to the minute.

How much sleep you need is individual

The US National Sleep Foundation recommends seven to nine hours for adults aged 18–64. Individual needs genuinely differ, though — some people function on six, others need nine. A practical way to find yours is the time you wake naturally, without an alarm, on a free day. If your weekday sleep is more than two hours shorter than that, you are likely accumulating sleep debt.

Falling asleep, and what helps

Healthy sleep onset latency is around 10 to 20 minutes. Falling asleep in under five is, counter-intuitively, a sign of insufficient sleep rather than good sleep. The fundamentals for better sleep onset are a consistent wake time, morning light exposure, and avoiding caffeine and alcohol before bed. Alcohol in particular shortens sleep onset while fragmenting the second half of the night, so overall quality falls. To check caffeine still in your system, see the caffeine calculator.