Find the ideal time to fall asleep or wake up, based on 90-minute sleep cycles, so you wake up feeling refreshed instead of groggy.
Calculate My Sleep Time ↓Based on 90-minute sleep cycles plus an average 15 minutes to fall asleep.
Going to bed and waking up at roughly the same time every day, including weekends, helps stabilise your circadian rhythm. Large swings between weekday and weekend sleep schedules — sometimes called "social jet lag" — can leave you feeling tired even after enough total hours of sleep.
Blue light from phones and screens can suppress melatonin production, the hormone that signals your body it's time to sleep. Dimming screens or switching to night mode an hour before bed, or simply putting devices away, helps your body wind down naturally.
Caffeine has a half-life of roughly 5-6 hours, meaning a coffee at 4pm can still have a meaningful amount active in your system at 10pm. Most sleep guidance suggests stopping caffeine intake at least 8-10 hours before your target bedtime.
A cooler bedroom, generally recommended around 18-20°C (65-68°F), supports the natural drop in core body temperature that helps trigger and maintain sleep. A room that's too warm is one of the more common, fixable causes of restless or interrupted sleep.
This calculator is built around the concept of sleep cycles — the roughly 90-minute pattern your brain moves through repeatedly during the night, cycling through light sleep, deep sleep, and REM sleep. Waking up at the end of a complete cycle, rather than in the middle of one (particularly mid-deep-sleep), is widely reported to feel less groggy, even at the same total number of hours slept. The calculator works backward or forward from your target time in blocks of 90 minutes, adding a standard 15-minute allowance for the time it typically takes to actually fall asleep after getting into bed.
This is a population-average estimate, not a personal biological measurement. Actual sleep cycle length varies somewhat by individual, age, and even night to night, and factors like stress, alcohol, or an irregular sleep schedule can all shift the pattern. Think of the calculator's suggested times as a useful planning tool for setting an alarm or bedtime, not a precise guarantee — if you consistently wake up groggy at a "cycle-aligned" time, your personal cycle length may simply run a bit longer or shorter than the 90-minute average.
Get your daily calorie and macro targets.
Open →Calculate your BMR and daily calorie burn.
Open →8 science-backed strategies to boost metabolism.
Read →Which is more effective for performance.
Read →