Sleep Calculator
Work out the best time to go to bed or wake up, based on 90-minute sleep cycles — so you wake up between cycles feeling refreshed, not mid-cycle and groggy.
A general guide. This calculator is a general guide based on your chosen sleep-cycle length and time to fall asleep (90 minutes and 15 minutes by default) — it is not medical advice. If you have ongoing trouble sleeping, speak to your GP or a healthcare professional.
Enter a time
Your suggested bedtimes or wake-up times appear here, based on your sleep cycle.
How sleep cycles work
Sleep happens in cycles of roughly 90 minutes, moving through light sleep, deep sleep and REM (dream) sleep. Waking up in the middle of a cycle — especially during deep sleep — tends to leave you feeling groggy, even if you've technically had enough hours. Waking up at the end of a cycle instead usually feels far more refreshing. This calculator adds an average 15 minutes to fall asleep, then counts back or forward in 90-minute blocks to suggest bedtimes or wake-up times that land you between cycles. Most adults do best with 5–6 full cycles a night (7.5–9 hours), which is highlighted as the recommended range.