How It Works
Gist calculates your biological age by analyzing health metrics from Apple Health and comparing them against research-backed optimal ranges.
Unlike your chronological age (years since birth), biological age reflects how well your body is actually functioning. A 40-year-old with excellent health markers might have a Gist Age of 35.
Step 1
Data Collection
Gist reads from Apple HealthKit. Works with Apple Watch, Oura, Whoop, Garmin, Fitbit, and any device that syncs to HealthKit.
Step 2
Metrics & Optimal Ranges
Each metric is scored 0-100 based on how close you are to the optimal range. Ranges are intentionally aspirational to encourage healthy habits. Higher-weighted metrics have more impact on your score.
Sleep
Quality rest is foundational to cellular repair and longevity.
| Metric | Optimal Range | Weight |
|---|---|---|
| Sleep Duration | 7.5-8.5 hours | 3x |
| Deep Sleep | 18-25% | 2x |
| REM Sleep | 20-25% | 2x |
Activity
Regular movement keeps your cardiovascular system young.
| Metric | Optimal Range | Weight |
|---|---|---|
| Daily Steps | 8,000-12,000 | 3x |
| Active Energy | 400-700 kcal | 2.5x |
| Exercise Time | 45-90 min | 2.5x |
| Distance | 6-10 km | 2x |
| Flights Climbed | 8-20 floors | 1.5x |
| Stand Hours | 10-14 hours | 1x |
Heart
Heart rate variability is one of the strongest predictors of biological age.
| Metric | Optimal Range | Weight |
|---|---|---|
| Resting Heart Rate(Lower is better) | 45-58 bpm | 3x |
| HRV (SDNN)(Higher is better) | 50-100 ms | 3x |
| Walking Heart Rate | 80-105 bpm | 2x |
| Respiratory Rate | 12-15 breaths/min | 1.5x |
| Average Heart Rate(All-day average) | 60-80 bpm | 1x |
Body
Physical fitness markers that correlate with longevity.
| Metric | Optimal Range | Weight |
|---|---|---|
| VO2 Max(Higher is better) | 42-55 mL/kg/min | 3x |
| Walking Speed(Higher is better) | 2.8-4.0 mph | 2x |
| BMI | 18.5-24.0 | 2x |
| Body Fat(Varies by sex) | 10-22% | 2x |
| Walking Steadiness | 80-100% | 1x |
Step 3
Scoring
Standard Scoring
Midpoint of optimal range = 100 points. Edges of optimal range = 80 points. Outside the range = penalty based on how far you deviate. This rewards hitting the sweet spot, not just being in range.
Lower-is-Better
For metrics like resting heart rate: at or below the lower bound = 100 points. Linear decrease through range (100 → 70). Penalty below 70 above upper bound.
Higher-is-Better
For metrics like HRV and VO2 Max: at or above the upper bound = 100 points. Linear increase through range (70 → 100). Penalty below 70 under lower bound.
Time Windows
Daily metrics (sleep, steps, heart rate, walking speed) use a 7-day average. VO2 Max uses a 180-day lookback with a 90-day freshness threshold. BMI and Body Fat use a 365-day lookback with a 180-day freshness check. Walking Steadiness uses a 30-day window. Stale data is excluded from scoring.
Estimated Cardio Fitness
When VO2 Max data is unavailable or stale, Gist estimates your cardio fitness from proxy metrics: walking speed, resting heart rate, active energy, exercise minutes, and walking heart rate. Requires at least 2 proxy metrics. The estimated score has slightly lower weight (2.5x vs 3x) since it's derived rather than directly measured.
Step 4
The Formula
Gist Age = Chronological Age + Age Offset
Age Offset = (50 - Overall Score) / 7.5 · Range: ±6.7 years
| Score | Age Offset | Meaning |
|---|---|---|
| 100 | -6.7 years | Exceptional health |
| 80 | -4 years | Excellent health |
| 50 | 0 years | Average health |
| 20 | +4 years | Below average |
| 0 | +6.7 years | Poor health markers |
Bonus
Pace of Aging
Beyond your Gist Age, we calculate your pace of aging — are you aging faster or slower than normal?
| Score | Pace | What it Means |
|---|---|---|
| 100 | -1.0x | Aging in reverse |
| 90 | -0.5x | Significant reversal |
| 80 | 0x | Stable / not aging |
| 65 | 0.5x | Aging slower than normal |
| 50 | 1.0x | Normal aging rate |
| 25 | 2.0x | Aging twice as fast |
| 0 | 3.0x | Accelerated aging |
Research
References
The optimal ranges used in Gist are based on established health research.