Nap Duration Calculator — evidence-based tool to check your nap duration. Includes formula, tips, and interpretation guide.
Wake-up time = Bedtime + 15 min (sleep latency) + (number of cycles × 90 min)
A standard adult sleep cycle lasts approximately 90 minutes and contains four stages: N1 (light sleep, ~5 min), N2 (light sleep, ~25 min), N3 (deep slow-wave sleep, ~25 min), and REM (~35 min). The proportions shift across the night — early cycles are deeper, later cycles have more REM. Waking during N3 produces sleep inertia (grogginess); waking from light N2 or between cycles produces alertness.
Worked example: bedtime 23:00 → 23:00 + 15 min = 23:15 sleep onset → 6 cycles = 9h → wake at 08:15. 5 cycles → wake at 06:45. 4 cycles → wake at 05:15.