Sleep calculator.
Use this free sleep calculator to get fast estimates, compare scenarios, and understand the numbers with clear step-by-step context.
Use the Sleep Calculator.
Results update automatically as you type. No account is required.
Enter your values
About the Sleep Calculator
Sleep happens in roughly 90-minute cycles, and waking at the end of a cycle — rather than in the middle of deep sleep — tends to leave you feeling more refreshed. This calculator suggests bedtimes for a chosen wake-up time, or wake-up times if you go to sleep now, aligned to full sleep cycles.
How it works
The calculator counts back (or forward) in 90-minute cycles and adds the time it typically takes you to fall asleep. Aiming for five to six complete cycles gives most adults the recommended 7.5 to 9 hours of sleep.
Reading the chart
You get the best option highlighted, with shorter and longer cycle counts listed so you can choose based on when you need to be up.
⚠ Disclaimer: This calculator provides general estimates for education only and is not medical advice. Individual needs vary with health conditions, medication, and body composition. Consult a qualified healthcare professional before making health, nutrition, or medical decisions.
FAQ
How many sleep cycles do I need?
Most adults do well on five to six cycles (about 7.5–9 hours). Four cycles (6 hours) is a minimum that leaves many people under-rested.
Why 90 minutes?
A full sleep cycle averages around 90 minutes, moving through light, deep, and REM stages. Cycle length varies between people, so treat times as a guide.
Does falling-asleep time matter?
Yes — that is why the calculator adds it. If it takes you 15 minutes to drift off, your bedtime should be 15 minutes earlier than the cycle math alone.