The Basic Formula for any exerciser to calculate his or her different heart rates for workouts of varied levels is straight-forward:

220 (226 if you’re a woman) — your age = your maximum heart rate or, put more plainly, your red-line pulse. Don’t you go there. The Basic Formula is the first formula in the Total Fitness Network calculator.

The result you get is called a "theoretical" or "age-predicted" or "estimated" maximum for a good reason: We are all different (thank goodness, huh?) with different Mom’s and Dad’s and different genes. That means some of our hearts will beat faster than that estimated maximum and still may not be maxed out. In contrast, some of our tickers will beat slower than that and we’ll be over the red-line into danger zone already.

So what’s a curious exerciser to do?

The best way to get a more accurate reading is to take a laboratory test, administered by exercise physiologists and testing professionals, offered at some colleges or fitness centers. They shovel you up on a treadmill, pop a Darth Vader-look-alike mask on you so they can measure all your expired air for oxygen and carbon dioxide. Then they keep speeding up the treadmill til you fly off the back and flatten against the back wall. Well, OK, so they stop it before you fly off, but you’re certainly staggering mightily. You are maxed out, and therefore you will know your maximum heart rate since they are logging it.

Oh, one caveat there: That’s assuming you are taking a test that has you doing an activity the same as the one you are used to doing, for example running. Because if you’re a swimmer, and you try to find your maximum heart rate by running, those ol’ runners’ muscles in your legs will give out before your heart reaches its max.

One answer to the dilemma is the Karvonen Formula, which is designed to take your fitness level into account by using your resting heart rate (usually, the more fit you are, the slower your ticker ticks when you’re resting).

This is the second formula in the Total Fitness Network calculator:

220 (226 if you’re a woman) — your age — your resting HR = HR + your resting HR = your maximum heart rate.

Next to laboratory tests, it becomes the second most accurate method for determining your heart rates.

But remember this: Without a truly accurate lab test, any heart rate that any formula calculates for you might be as much as 10-15 beats off in either direction. Your genes getting into the act again. That’s where you need to use your smarts to narrow down what’s right for you once you’ve done a calculation for your estimate.

If what the formula says feels too hard, back off; if it feels too easy, go harder. It won’t take long for you to hone in on what’s right. But at least with the formula, you’ll have an idea where to start.

If you're confused about maximums, training, target, or resting heart rates, take a look at that vocabulary story in the Total Fitness Network guide to heart-rate training.