Five thousand Norwegians “ran to the point of exhaustion on a treadmill” so you wouldn’t have to. They were research subjects whose measurements went into a new online fitness age calculator made by exercise researchers at the Norwegian University of Science and Technology, The New York Times reports. The calculator lets people find how fit they are with just a couple of easy-to-get measures, waist circumference and resting heart rate.

Such a calculator may help doctors take better stock of their patients’ heart disease risk, the calculator’s makers wrote in a paper they published about their work. Of course, it’s also just fun (or scary, depending) to try at home. The Times explains how to take your heart rate for this calculator. The online calculator is here.

So what exactly does your number mean? If you get a fitness age of 40, for example, then you have the “typical, desirable” fitness of a 40-year-old, The New York Times reports. A young fitness age is “the single best predictor of current and future health,” the research team’s senior member, Ulrik Wisloff, told The Times.

The Times explains in detail all of the logical steps and assumptions the calculator must make to calculate your fitness over the internet, without making you run for your life. In brief, the calculator uses other measures to estimate people’s oxygen consumption during maximum exercise, which in turn is a strong predictor of lifespan. The calculator is fairly accurate, but not perfect. It’s a “rough estimate of cardiorespiratory fitness,” the researchers wrote in their paper, published in the journal Medicine & Science in Sports & Exercise.

The New York Times