Sleep cycle calculator
Work backward or forward from a target time using 90-minute sleep cycles.
Each cycle runs about 90 minutes, and it typically takes ~14 minutes to fall asleep. Waking up between cycles — rather than mid-cycle — tends to feel far less groggy.
Why 5–6 cycles?
Most adults need 7–9 hours of sleep, which lines up with 5 to 6 complete 90-minute cycles. Fewer than 5 cycles regularly is linked with daytime grogginess; consistently needing more may be worth mentioning to a doctor.
Cycle length varies by person and by night. Use this as a starting point, not a strict formula.