This test can calculate your biological age for free. Here's how it works — and how to interpret the results.

• Biological age tests are becoming popular with biohackers and longevity seekers.
• They're not perfect health indicators, but they may tell you a little something about your aging body.

There are a lot of ways to spend a fair amount of money calculating your so-called "biological age." As a longevity reporter who's been covering the science of aging and age-related diseases for a few years now, I am well aware of the drawbacks and limitations of the various biological aging tests out there.

TruDiagnostic, one of the most widely used and respected direct-to-consumer biological age tests, charges $500 to pump out a biological age estimate and a predicted pace of aging based on dried blood samples. David Sinclair's popular new startup, Tally Health, is cheaper but less comprehensive. Tally analyzes cheek swabs for about $200, and often recommends pricey supplements afterwards that the company says can "help lower" your biological age.

But I found a way to calculate my biological age that doesn't require any extra money — only some basic lab results that I got for free at a recent annual exam. With information that I already had stored in my phone, I discovered I may be — biologically speaking — about 9 years 'younger' than my driver's license suggests.

I'm not shouting this information from the rooftops, or feeling smug towards my baby brother as a result. Instead, I'm taking this as a sign that I'm aging at a fairly healthy clip, and that I should probably continue executing four important and straightforward health-promoting moves as often as I can.

My free biological age calculation estimated my risk of premature death or disease

At its essence, any good biological age test is trying to capture the fitness of your body parts. It's interpreting information extracted from your blood, spit, or skin, and then using that information to try to assess how your body is operating. It's trying to pin down a number for how aged or youthful your body is really acting — regardless of the number of candles you put on the cake this year.

There are several ways to calculate a biological age, and scientists don't yet agree on which is best. Some of the most respected biological age tests are epigenetic clocks, sometimes called DNA methylation tests. Other clocks incorporate external factors like smoking history, or chronological age into a biological age calculation.

I did a "phenotypic age" test, which has been shown to help predict your odds of developing a broad array of health issues generally associated with aging and age-related decline, like heart and lung problems, cognitive issues, and Type 2 diabetes.

"It shows very strong associations with future risk of developing various chronic diseases — including heart disease," Dr. Nour Makarem, a cardiovascular epidemiologist at Columbia University who studies how sleep, diet, and exercise impact our heart health, told Business Insider.

Makarem has used phenotypic age measurements in studies of thousands of US adults. She has shown that this type of biological age is not only predictive of future disease and early death, but that it can also be quickly modified by what we do and what we eat every day. Getting better sleep, eating a slightly healthier diet, moving just a little bit more, and stopping smoking can all have a serious impact on our phenotypic age.

In one study published last November, Makarem showed that middle-aged people with good heart health were, on average, about five years "younger" than their real age, physiologically speaking. Those with poor heart health were biologically older than their years, aging faster than time.

The benefits of free biological age testing

Learning your own biological age is one simple way to approximate how well your body is weathering the test of time.

At their best, biological age tests may help encourage people to do more of the things that will subtly improve their longevity — like eating healthy foods and moving enough — keeping us nimbler and sharper into later years. At their worst, these tests may embolden optimistic biohackers to assume they can cheat death or prevent age-related diseases entirely.

Experts also caution that biological age tests shouldn't be taken too seriously yet, because they're not perfect indicators of your overall health. The science of biological aging is still a bit squishy, as it is a relatively new field.

A biological age test can never know if you're about to get run over by a bus, and it may also miss important health issues on the horizon. Conversely, it could scare you into thinking you're in "older" shape than your age, even if you're in relatively good health. This is why the tests should always be taken into consideration in conjunction with other, more tried-and-true health indicators, like your waist circumference, blood pressure, and cholesterol levels, for example.

But, if this is your first foray into studying your own biological age, the free phenotypic version I did may be enough of a benchmark for you. With nine lab measurements from your annual physical, including your white blood cell concentration, and blood glucose, you can choose from one of several free online calculators, and have a first biological age estimate in minutes.

These 4 behaviors can potentially lower your biological age

While I'm thrilled that my biological age appears to be lower than my actual age, I don't think it's any special pride point worth bragging about. It's just a sign that my insides are aging in a relatively healthy way. If I change my habits to exercise less or eat more junk, my number could easily shift. To me, the test results are a gentle nudge saying "you're doing great, don't stop now."

Makarem likes to remind herself that she doesn't have to make dramatic changes in her life to have a positive impact on her own biological age, either. Eating just a bit better, moving just a bit more, these actions can have a measurable impact on your biological age result.

"People get overwhelmed sometimes with those results because they think, 'oh, I just have to have a perfect diet and perfect physical activity,' and that's not actually how it is. Even if you make a small change, it can have a benefit," she said.

Simple choices like getting up to take a quick walk, or choosing a healthier snack really can make a gentle, almost imperceptible but important difference over time.

Longevity expert Steve Horvath, who pioneered the science of biological aging, and who has developed some of the most well-respected biological clocks around, has seen this firsthand. He found that when he made small, healthy tweaks in his life including eating more vegetables, and taking a brisk walk each night after dinner, his biological age measurement went down by four years in just nine months.

"Everything you know about a healthy lifestyle does seem to affect these biomarkers," he recently told BI.