This content is for informational purposes only and is not a substitute for professional advice.
Fuel Age is a unique health metric that estimates how your lifestyle and habits are affecting your biological age compared to your actual age. By analyzing your sleep, activity, heart health, and other key factors from your wearables and daily inputs, Fuel calculates whether your body is aging faster, slower, or at the same pace as your calendar age.
Each week, Fuel also tracks your "pace of aging," showing if your recent habits are helping you rejuvenate, stay stable, or accelerate aging. This makes it easy to see how changes in your routine—like improving sleep or increasing activity—can help you stay younger, healthier, and more resilient over time.
Fuel Age works by comparing your recent health habits—like sleep, activity, heart health, and body composition—to science-backed targets for your age and sex. If your habits are better than average, your Fuel Age can be lower than your real age, showing you’re aging more slowly. If your habits fall short, your Fuel Age may be higher, signaling faster aging. Each factor, such as sleep hours or daily steps, has a different impact on your score, so small improvements in key areas can help you “rejuvenate” over time.
How Fuel Age is calculated
Fuel Age(t) = Chronological Age + Σ wᵢ · Δᵢ(180 d)
where each Δᵢ(180 d) is the six-month deviation of metric i from an evidence-based target (positive values raise age, negative values lower it).
Initial weights
| Metric | Initial weight effect |
|---|---|
| Sleep hours | w₁ = 0.15 yr per –1 h/night |
| Sleep timing regularity | w₂ = 0.10 yr per –10% consistency |
| Moderate-zone minutes | w₃ = 0.08 yr per –30 min/week |
| High-zone minutes | w₄ = 0.12 yr per +15 min/week above guideline |
| Strength minutes | w₅ = 0.06 yr per –20 min/week |
| Daily steps | w₆ = 0.07 yr per –2,000 steps/day |
| Resting heart rate | w₇ = 0.20 yr per +5 bpm |
| VO₂ Max | w₈ = 0.18 yr per –3 ml·kg⁻¹·min⁻¹ |
| Lean mass index | w₉ = 0.04 yr per –1 kg/m² |
All inputs are age- and sex-adjusted z-scores before conversion to the year offsets above. Coefficients may be updated as more data becomes available.
Your Pace of Aging score shows whether your body is getting biologically younger, staying the same, or aging faster based on your recent habits. Each week, Fuel looks at your last five Fuel Age results and calculates the trend—if your Fuel Age is dropping, you’re rejuvenating; if it’s rising, you’re aging faster. The score is easy to read: negative numbers mean you’re getting younger, zero means stable, and positive numbers mean accelerated aging. The further from zero, the faster the change.
How it’s calculated
Pace of Aging for week k:
To help you understand what’s driving changes in your Pace of Aging, Fuel highlights the top three health factors that had the biggest impact on your score each week. This means you’ll see which habits—like sleep, activity, or heart health—most influenced whether you’re aging faster or slower, so you know where to focus your efforts.
How it works:
For each metric i, compute Weekly Impactᵢ = wᵢ · (Δᵢ(30 d) – Δᵢ(prev 30 d)). Rank by |Weekly Impact|, keep the three largest. Their signed values explain the direction and magnitude of the current pace change.
