Wake up at the end of a natural 90-minute sleep cycle so you feel more refreshed instead of groggy.
A typical sleep cycle lasts about 90 minutes and includes light sleep, deep sleep and REM. Waking at the end of a cycle (rather than in the middle of deep sleep) reduces sleep inertia and helps you feel more alert.
Sleep typically moves in cycles of about 90 minutes, including light, deep and REM stages. Waking near the end of a cycle often feels easier than waking mid-cycle.
Most adults do well with 4–6 cycles (roughly 6–9 hours). Quality and consistency matter as much as the exact count.
It is a useful average, not a fixed law. Individual cycle length varies. Use the calculator as a guide and adjust from how you feel.
Prioritise a consistent schedule and wind-down routine. Even improving sleep quality for 6–7 hours often helps more than occasional long lie-ins.