Two people can both be 65 years old, yet one climbs stairs with ease while the other struggles to cross a room. The difference is biological age, which describes how well your body is actually functioning rather than how many birthdays you have counted. Scientists increasingly measure biological age using biomarkers, which are objective, repeatable measurements that predict health and survival. The good news is that you do not need a fancy lab to start. Here are seven of the best-studied aging biomarkers, what each one tells you, the ranges to aim for, and how to measure them.
1. Cardiorespiratory Fitness (VO2max)
VO2max measures how much oxygen your body can use during hard exercise, and it is one of the strongest predictors of how long you will live. In a JAMA Network Open study of 122,007 patients undergoing treadmill testing, researchers found that higher cardiorespiratory fitness was tied to lower death rates with no upper limit to the benefit, and the very fittest people had the lowest risk of all (JAMA Network Open, Mandsager et al., 2018). The same line of research has found fitness to be a more powerful predictor of mortality than well-known risks like high blood pressure, smoking, or diabetes, with each one-MET gain in fitness (about 3.5 ml/kg/min) linked to roughly a 13 to 15 percent lower risk of death.
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How to measure it: A precise VO2max test is done in a lab or sports clinic, but many smartwatches now estimate it from your heart rate during walks and runs. A simple home proxy is how winded you feel climbing two flights of stairs or walking briskly uphill. The practical takeaway is that moving from the least-fit category into even a slightly higher one delivers large gains, so regular brisk walking, cycling, or swimming pays off.
2. Grip Strength
How hard you can squeeze is a surprisingly powerful window into whole-body aging. Researchers have described grip strength as a potential biomarker of aging because it predicts all-cause death across both sexes and across age groups (Bohannon, Age and Ageing, 2015; reviewed in NIH/PMC, 2025). In one analysis, handgrip strength was an even stronger predictor of overall and cardiovascular death than systolic blood pressure, and a one-standard-deviation drop in grip strength was tied to higher mortality risk. Weakening grip often signals broader muscle loss, known as sarcopenia, and frailty.
How to measure it: An inexpensive handgrip dynamometer (often under $30) gives you a number in pounds or kilograms you can track over time. No device handy? Pay attention to real-world signs like trouble opening jars, carrying groceries, or twisting off bottle caps. Resistance training and simply using your hands more can rebuild grip strength at any age.
3. Walking (Gait) Speed
How fast you walk has been called the sixth vital sign, and the evidence is striking. A landmark pooled analysis in JAMA of 34,485 older adults found that gait speed predicted survival at every age past 65 (Studenski et al., JAMA, 2011). In that study, a walking speed of about 0.8 meters per second matched average life expectancy for a person's age and sex, while speeds of 1.2 meters per second or faster predicted exceptional longevity. Speeds slower than roughly 0.6 meters per second flagged higher risk of early death.
How to measure it: This is the easiest test on the list. Mark a 4-meter (about 13-foot) path, walk it at your normal comfortable pace, and time yourself with a stopwatch or phone. Divide the distance by your time in seconds to get your speed in meters per second. Because the test is so simple, it is easy to repeat every few months and watch the trend, which matters more than any single reading.
4. Resting Heart Rate and Heart Rate Variability
Your resting heart rate, the number of beats per minute when you are calm and still, reflects how efficiently your heart works. A meta-analysis in CMAJ pooling more than one million people found that every 10-beat-per-minute increase in resting heart rate was associated with about a 9 percent higher risk of death from any cause and roughly an 8 percent higher risk of cardiovascular death (Zhang et al., CMAJ, 2016). People with resting rates above 80 beats per minute carried notably higher cardiovascular risk. A healthy resting rate for most adults falls between about 60 and 100 beats per minute, and fitter people often sit toward the lower end.
Heart rate variability (HRV), the natural beat-to-beat variation in your pulse, is a related marker. Higher HRV generally signals a more adaptable nervous system, while declining HRV has been linked to frailty and poorer physical function in older adults (NIH/PMC observational studies). How to measure both: Place two fingers on your wrist or neck first thing in the morning and count beats for 60 seconds, or let a fitness tracker, smartwatch, or many blood pressure cuffs do it automatically. Regular aerobic exercise tends to lower resting heart rate and raise HRV over time.
5. Blood Pressure
Blood pressure measures the force of blood against your artery walls, and keeping it in range protects your heart, brain, and kidneys for decades. Under the 2017 American College of Cardiology and American Heart Association guideline, normal is below 120 over 80 mm Hg, elevated is 120 to 129 over below 80, stage 1 hypertension is 130 to 139 or 80 to 89, and stage 2 is 140 or higher or 90 or higher (Whelton et al., 2017 ACC/AHA Guideline). Risk rises steadily as readings climb above normal, which is why the guideline lowered the threshold for diagnosing high blood pressure.
How to measure it: Home blood pressure monitors with an upper-arm cuff are affordable and accurate. Sit quietly for five minutes, keep your feet flat and arm supported at heart level, and take readings at the same time each day. Because pressure fluctuates, an average of several measurements over days tells you more than one number. Share your home log with your doctor, who can confirm readings in the office.
6. Fasting Glucose and HbA1c
Blood sugar control is central to healthy aging, and two numbers tell the story. Fasting glucose is a snapshot taken after not eating overnight, while HbA1c reflects your average blood sugar over the past two to three months. According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), an A1C below 5.7 percent is normal, 5.7 to 6.4 percent indicates prediabetes, and 6.5 percent or higher on two tests indicates diabetes (NIDDK, The A1C Test and Diabetes). For fasting glucose, below 100 mg/dL is normal, 100 to 125 mg/dL is prediabetes, and 126 mg/dL or higher signals diabetes (NIDDK/ADA criteria).
How to measure it: Both are simple blood tests your doctor can order, often as part of a routine annual checkup. Home glucose meters and newer continuous glucose monitors can track fasting and daily levels, though A1C is best run by a lab. Because prediabetes is common and often silent in adults over 50, knowing these numbers early gives you time to act, and weight loss, exercise, and dietary changes can move them in the right direction.
7. Inflammation (hs-CRP)
Chronic, low-grade inflammation, sometimes called inflammaging, is a recognized driver of age-related disease, and the high-sensitivity C-reactive protein (hs-CRP) blood test is the most common way to measure it. The American Heart Association considers an hs-CRP below 1.0 mg/L low risk, 1.0 to 3.0 mg/L average risk, and above 3.0 mg/L higher risk for cardiovascular events. In a community cohort study, people in the highest hs-CRP group had nearly double the risk of death compared with those in the lowest group, and research on long-lived populations consistently shows lower inflammation markers (NIH/PMC cohort studies; PolSenior study, 2016).
How to measure it: hs-CRP is a simple blood test you can ask your doctor to add to routine bloodwork; it is not yet a standard part of every checkup, so you may need to request it. One caveat: a recent cold, infection, or injury can temporarily raise the number, so it is best measured when you are well. Of all seven markers, hs-CRP is among the most responsive to lifestyle, and studies report that exercise, weight loss, and a better diet can lower it meaningfully within a few months.
Putting It All Together
No single number defines your biological age, but together these seven markers paint a clear picture of how your body is aging and where you have room to improve. Several, including gait speed, grip strength, resting heart rate, and blood pressure, you can begin tracking at home this week with little more than a stopwatch, a tracker, or an inexpensive cuff. The rest are quick additions to a routine blood draw. What ties them together is a hopeful theme that runs through the research: these are not fixed verdicts but moving targets, and the same habits, regular movement, strength work, good sleep, and a sensible diet, tend to push nearly all of them in a healthier direction.
<strong>Curious about your own number?</strong> realBioAge.com estimates your true biological age in minutes from simple, science-based inputs — then shows you what's aging you faster and what to do about it. <a href="https://realbioage.com" target="_blank" rel="noopener">Take the realBioAge test →</a>
This article is educational and not medical advice. Talk with your doctor about your numbers and testing.