90 – 100	Excellent — optimal recovery and sleep quality
80 – 89	Good — solid, restorative sleep
70 – 79	Fair — room for improvement
Below 70	Poor — review habits and environment

7 – 9h	Optimal for adults 18–64 (NSF)
6 – 7h	May be sufficient but not ideal
< 6h	Sleep deprivation — health risks increase
> 9h	Oversleeping — may indicate underlying issues

13 – 23%	Healthy range of total sleep
60 – 120 min	Typical duration per night

Critical for physical recovery, immune function, and memory consolidation. Naturally decreases with age. Improved by exercise, consistent schedule, and cool bedroom (18–19°C).

40 – 50	Elite athlete level
50 – 60	Very good fitness
60 – 70	Good / above average
70 – 80	Average
> 80	Below average — consult a doctor if persistent

A downward trend indicates improving cardiovascular fitness. Sudden spikes (+5 bpm) may signal illness, stress, or overtraining.

Target: vary bedtime by ≤30 minutes daily.

Irregular sleep disrupts circadian rhythm and reduces sleep quality even with adequate duration. "Social jet lag" (weekend vs weekday difference >1h) is linked to metabolic and cardiovascular risks.

Tip: Set a fixed wake time — it anchors your sleep schedule more than bedtime.

Environment: Dark, cool (18–19°C), quiet.
Timing: No caffeine 8h before bed. No alcohol 3h before.
Screens: Blue light filter 2h before sleep or use night mode.
Exercise: Regular activity improves sleep quality, but avoid intense workouts 2–3h before bed.
Naps: Limit to 20–30 min before 3pm. Longer naps disrupt nighttime sleep.