FAQ

10 common questions about sleep cycles.

Q1. Is 90 minutes really universal?

Studies show cycles vary from 70 to 120 minutes individually. 90 is the population average. Your own cycle may be shorter or longer — experiment by setting alarms ±15 minutes and observe which feels best.

Q2. Does the "fall-asleep buffer" matter?

Yes. If you set an alarm 7.5h from lights-out but fall asleep 20 minutes later, you are waking at 7h 10min, likely mid-cycle. The 14-minute buffer approximates average sleep onset.

Q3. Can I shortcut by napping with cycles?

Power naps work best at 20 minutes (light sleep only) or 90 minutes (full cycle). Avoid 30–60 minute naps — you enter deep sleep but wake before cycle completion.

Q4. What about REM-focused alarms (e.g. Sleep Cycle app)?

Phone-based trackers use accelerometers/mics to detect movement patterns. They are approximate but can improve waking quality. This calculator is complementary: set the target time based on cycles, then let the app fine-tune within a 30-min window.

Q5. Do children and teens need different cycles?

Cycle length is similar, but total sleep need is higher: teens 8–10h (5–6 cycles), children 9–12h (6–8 cycles). Our calculator shows up to 6 cycles; teens should aim for the upper end.

Q6. Does caffeine shift my cycle?

No, but it delays sleep onset (more buffer time) and reduces deep sleep percentage. Stop caffeine 8 hours before bed.

Q7. Alcohol makes me sleepy — is that OK?

Alcohol induces faster onset but cuts REM and causes mid-cycle waking 2–3 hours later. Total sleep quality decreases even if subjective tiredness is reduced.

Q8. How do I fix sleep debt?

Add 1 cycle (90 min) earlier for 2–3 weeks. Going to bed 1.5h earlier is easier to sustain than sleeping in on weekends, which shifts your rhythm.

Q9. Does jet lag disrupt cycles?

Yes. Expect 1 day per time zone to re-sync. Anchor meal times and morning sunlight on the new schedule to speed adaptation.

Q10. Is this tool medical advice?

No. It is informational. If you have chronic insomnia, apnea symptoms, or other sleep disorders, consult a healthcare provider.