Biological age: estimate yours from heart and fitness data

A biological age calculator estimates how old your body seems compared with your age in years, using signals that research links to health and lifespan. Wearable-based calculators usually start from your chronological age and adjust it with fitness (VO2 max), resting heart rate, daily activity and sleep regularity. The result is an estimate with a range, not a measurement.

Different methods give different answers. Epigenetic clocks read DNA methylation in a blood sample, heart age uses blood pressure and other risk factors, and wearable calculators use heart and activity data. Each is useful for tracking yourself over time with the same method. None of them can tell you how long you will live. This guide explains the methods, the evidence behind each input, and how to read your result. For how these signals feed daily readiness, see the recovery score explained.

What is biological age?

Biological age is an estimate of how far your body has aged, based on measurable markers, as opposed to chronological age, which counts years since birth. Two people born on the same day can have different biological ages if their fitness, heart health or other markers differ. It is a research concept with several competing definitions.

The research versions were built to predict outcomes. For example, the DNA methylation clock called DNAm PhenoAge was developed from clinical measures linked to lifespan and healthspan, and it predicted all-cause mortality, cancers, physical functioning and Alzheimer's disease better than earlier clocks. Consumer calculators borrow the same idea with inputs you can measure at home.

How do biological age calculators work?

Biological age calculators combine markers that predict health outcomes, then express the result in years. Lab methods use DNA methylation or blood tests. Risk-factor calculators, like heart age, use blood pressure, BMI, smoking and diabetes. Wearable calculators use resting heart rate, HRV, VO2 max, activity and sleep data. Each method answers a slightly different question.

Method	Inputs	What it estimates	Practical notes
Epigenetic clock (for example DNAm PhenoAge)	DNA methylation from a blood sample	Molecular aging linked to mortality and disease	Lab test; different clocks give different ages
Heart age (Framingham-based)	Age, sex, blood pressure, BMI, smoking, diabetes	Age of your vascular system	Free online versions; no wearable needed
Fitness age	VO2 max, measured or estimated	Age at which your fitness is average	Estimated VO2 max has a wide error
Wearable-based estimate	Resting heart rate, HRV, VO2 max, sleep, activity	Composite of signals linked to outcomes	Updates as your data changes

Sources: Levine et al. 2018; Yang et al., MMWR 2015.

What is heart age?

Heart age is the predicted age of your vascular system based on your cardiovascular risk factors. The CDC used the non-laboratory Framingham risk score with US survey data for adults aged 30 to 74. On average, men's heart age was 7.8 years older than their chronological age, and women's was 5.4 years older.

Heart age varied by group and state. It was lowest in Utah, at 5.8 excess years for men and 2.8 for women, and highest in Mississippi, at 10.1 and 9.1 years. The CDC authors suggested that heart age can simplify risk communication. It does not use wearable data, so it complements rather than replaces heart rate and fitness signals.

Which signals predict aging and health?

Cardiorespiratory fitness, resting heart rate, daily steps and sleep regularity each predict mortality in large studies. Fitness has the strongest and most consistent associations. These are the signals a wearable can measure or estimate, which is why wearable-based biological age estimates rely on them.

Signal	Key finding	Study
Cardiorespiratory fitness (VO2 max)	Each 1-MET higher fitness: 13% lower all-cause mortality	Kodama et al., JAMA 2009, 33 studies, 102,980 people
Fitness, lowest vs elite	Adjusted hazard ratio 5.04 for death	Mandsager et al., JAMA Netw Open 2018, 122,007 patients
Resting heart rate	Each 10 bpm higher: 9% higher all-cause mortality	Zhang et al., CMAJ 2016, 46 studies
Daily steps	Highest vs lowest quartile (about 10,900 vs 3,550 steps): 53% lower mortality	Paluch et al., Lancet Public Health 2022, 47,471 adults
Sleep regularity	More regular sleep: 20% to 48% lower all-cause mortality vs least regular	Windred et al., Sleep 2024, 60,977 adults

All findings are associations from observational studies. They describe groups, not individual futures.

Two details matter for reading these numbers. Steps showed diminishing returns: risk kept falling up to about 6,000 to 8,000 steps a day in adults 60 and older, and 8,000 to 10,000 in younger adults. And sleep regularity predicted mortality better than sleep duration in that UK Biobank analysis. For VO2 max norms, see VO2 max by age. For resting heart rate norms, see the resting heart rate by age chart.

How accurate is a biological age estimate?

A biological age estimate is only as accurate as its inputs and the model behind it. Wearable-based estimates combine values that each carry error, such as an estimated VO2 max, with population associations. That makes them useful for tracking change in yourself, not for comparing with a friend or a lab test.

The VO2 max input shows the problem. A non-exercise estimate from age, sex, body composition and self-reported activity had a standard error of about 5.3 to 5.6 ml/kg/min in the original validation. That is a wide band. A good calculator therefore shows a likely range, and makes the range wider when fewer or less precise signals are available. See how to improve VO2 max for the input that tends to move most with training.

Can you lower your biological age?

You can change the signals that wearable-based biological age estimates use. Fitness, resting heart rate, daily steps and sleep regularity all respond to habits over weeks to months. If those signals improve, the estimate improves. Whether that changes your actual lifespan is not proven for any single person.

Signal	Habit linked to improvement
VO2 max	Regular aerobic training
Resting heart rate	Endurance training, yoga, enough sleep, less evening alcohol
Daily steps	More walking across the day
Sleep regularity	A consistent bedtime and wake time, including weekends

For practical steps, see how to lower your resting heart rate. The US physical activity guideline of 150 to 300 minutes of moderate or 75 to 150 minutes of vigorous activity a week is a reasonable starting target for the fitness inputs.

What should you do with a high biological age result?

A high biological age estimate is a prompt to look at the inputs, not a diagnosis. Check which factor added the most years: low fitness, a high resting heart rate, few steps or irregular sleep. Those are the places to start. If you also have symptoms or known risk factors, such as high blood pressure, talk to a doctor.

Wearable estimates can not measure blood pressure, cholesterol or blood sugar, which drive heart disease risk. A doctor's check of those numbers adds information no wearable can provide.

How Svanu estimates biological age

Svanu estimates biological age from your chronological age plus at least 2 of 5 signals: resting heart rate, HRV, VO2 max, sleep consistency and activity. It shows a likely range, which is wider when fewer signals are available, and it shows how each factor adds or takes away years, so you can see what drives the result.

VO2 max comes from Apple Health when your watch writes it. Otherwise the app calculates an estimate and labels it as one: from resting heart rate and age (the Uth-Sorensen ratio), or without resting heart rate from age, sex, BMI and average daily steps (based on Jackson et al. 1990). All calculations run on your iPhone, and there is no health database on a server. See the Svanu home page for what is included free.