Calculate the best times to wake up or go to bed based on 90-minute sleep cycles — so you wake feeling refreshed instead of groggy.
Enter your figures and click Calculate to see your results.
Choose whether you want to know when to wake up or when to go to sleep, enter the relevant time and your average time to fall asleep.
Press the Calculate button. Results appear instantly using standard clinical and scientific formulas.
Results are displayed with all key values clearly labelled. Use the Copy button to grab your results or Download to save a text file. For health decisions, always consult a healthcare professional.
A sleep cycle lasts approximately 90 minutes and consists of four stages: NREM Stage 1 (light, transitional sleep), NREM Stage 2 (deeper sleep, heart rate slows), NREM Stage 3 (deep/slow-wave sleep — most restorative), and REM sleep (dreaming, memory consolidation, emotional processing). A full night contains 4–6 complete cycles.
Waking mid-cycle — especially from deep NREM sleep — causes "sleep inertia": the groggy, disoriented feeling that can persist for 30–60 minutes. Waking at the natural end of a cycle, when sleep is at its lightest, feels much easier and more refreshing. This calculator suggests wake times that align with cycle boundaries.
The American Academy of Sleep Medicine recommends 7–9 hours per night for adults aged 18–64. Adults 65+ need 7–8 hours. Individual needs vary — some adults genuinely function well on 7 hours while others need 9. The true test: can you wake without an alarm feeling alert? If you regularly need an alarm and feel tired, you are likely sleep-deprived.
Sleep debt is the cumulative effect of insufficient sleep. Short-term debt (1–2 nights) can be largely recovered with additional sleep over the following days. Chronic sleep debt (weeks or months) is more serious — some cognitive and metabolic effects persist even after recovery sleep. Consistent, adequate nightly sleep is far more effective than trying to "catch up" on weekends.
The most evidence-based sleep hygiene practices: maintain consistent sleep and wake times daily (including weekends), keep your bedroom cool (16–19°C/61–67°F), dark and quiet, avoid screens 30–60 min before bed (blue light suppresses melatonin), limit caffeine after 2pm, avoid large meals and alcohol close to bedtime, and get regular morning sunlight exposure.
