Sleep Calculator
Find the best times to sleep and wake based on 90-minute sleep cycles. Wake up refreshed instead of groggy by timing your alarm to natural cycle endings.
Why Sleep Cycles Matter
A complete sleep cycle lasts about 90 minutes and includes light sleep, deep sleep, and REM sleep. Waking up mid-cycle — especially during deep sleep — leaves you feeling groggy (that's called "sleep inertia"). Timing your alarm to the end of a cycle means you wake during lighter sleep, feeling more alert.
Most adults need 5-6 complete cycles (7.5-9 hours). Less than 4 cycles regularly is linked to impaired cognitive function, weakened immunity, and increased risk of chronic disease. The National Sleep Foundation recommends 7-9 hours for adults aged 18-64.
Tips for Better Sleep
Keep a consistent schedule (even weekends). Avoid screens 30-60 minutes before bed. Keep your room cool (65-68°F / 18-20°C). Avoid caffeine after 2 PM. These basics matter more than any supplement or gadget. And stay hydrated during the day — use our Water Intake Calculator — but taper off in the evening to avoid midnight bathroom trips.
⚠️ Medical Disclaimer
This tool provides estimates for informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making health decisions. Results may vary based on individual factors not captured by this calculator.