Sleep Calculator
Set your time and press
Calculate Sleep Times
Recommended Bedtimes
Sleep Calculator Guide
Sleep occurs in repeating 90-minute cycles, each containing four stages — light sleep, two deeper stages, and REM (dream) sleep. Waking at the end of a complete cycle means you rise from light sleep, leaving you refreshed. Waking mid-cycle (especially from deep sleep) causes sleep inertia — the heavy, groggy feeling that can last 30–60 minutes.
Want to wake up at 6:30 AM with 14 min fall-asleep time:
Stage 1 — Light
Transition to sleep. Lasts 1–7 min. Easily woken. Muscles relax.
Stage 2 — Light
Heart rate slows, body temp drops. 10–25 min. Memory consolidation begins.
Stage 3 — Deep
Tissue repair, immune boost, hormone release. Hardest to wake from.
REM Sleep
Dreaming, emotional processing, creativity & learning consolidation.
Wake Up Energised
Aligning your alarm to cycle end means you rise from light sleep — no grogginess.
Better Focus
Full REM cycles improve memory, learning, and daytime cognitive performance.
Physical Recovery
Deep sleep releases growth hormone essential for muscle repair and immune health.
Q1: How many sleep cycles do I need?
Most adults need 5–6 complete cycles (7.5–9 hrs) per night. Athletes or those recovering may benefit from 6 cycles (9 hrs).
Q2: Why is 7 hrs worse than 7.5 hrs?
7 hours cuts mid-cycle, waking you from deep sleep. 7.5 hours (5 full cycles) ends right at the boundary — you wake up feeling natural and alert.
Q3: What is sleep inertia?
The groggy, disoriented feeling when woken mid-cycle (especially from deep sleep). It can last 15–60 minutes. Cycle-aligned waking eliminates this.
Q4: Can I use this for naps?
Yes! Aim for 20 minutes (power nap, before deep sleep) or a full 90 minutes (one complete cycle). Avoid 30–60 min naps — they often end in deep sleep.