Sleep Cycle Bedtime Calculator

What it measures

This calculator estimates the best times to fall asleep or wake up based on your target time and the natural 90-minute rhythm of human sleep cycles. It is designed to help you plan your sleep so that you wake up at the end of a cycle — when sleep is lightest — rather than mid-cycle, which is when you are most likely to feel groggy.

How it works

You enter either the time you need to wake up or the time you plan to go to bed. The calculator adds approximately 15 minutes of sleep-onset latency (the average time a rested adult takes to fall asleep), then counts backwards or forwards in 90-minute increments to find four cycle-aligned options. Options covering 5–6 cycles (7.5–9 hours) are highlighted as most suitable for the majority of adults.

Tips for an accurate result

• 1Keep a consistent schedule — Going to bed and rising at the same time every day — including weekends — is one of the strongest evidence-based ways to improve sleep quality and daytime alertness.
• 2Avoid screens in the final hour — Blue-light exposure from phones and tablets suppresses melatonin release and can delay sleep onset well beyond the average 15 minutes.
• 3Don't rely on the weekend lie-in — Sleeping in at weekends to compensate for a short week (social jet lag) disrupts your circadian rhythm and rarely fully repays the debt.
• 4Note how you feel, not just the clock — Cycle lengths vary between individuals and change across the night. If a suggested time consistently leaves you groggy, shift it by 10–15 minutes and observe.
• 5Limit caffeine after 2 pm — Caffeine has a half-life of roughly 5–6 hours, so an afternoon coffee can still be in your system at bedtime, increasing latency beyond the assumed 15 minutes.