The quick answer: probably not. I actually wrote a longer piece about this in the old StrongFast Planet newsletter.
But let's take a step back. Why would anyone want to know their maximum heart rate anyway?
One of the common reasons is to find "target zones" especially the alluring "fat-burning zone." These are all based off of your MHR and are not particularly helpful. The other, more useful, reason is to gauge your intensity level. It's one thing to think we're working hard; it's another to know it based on our MHR.
The history of this formula is actually kind of amusing: it was never intended to be authoritative. It was just an observation on a small sample.
So back to its accuracy. Personally, I like the way Olympic speed skating champion Eric Heiden (now MD) put it in his book Faster, Better, Stronger with Max Testa, MD:
Medically speaking, the 220-age formula has a standard deviation of 12 beats/min (bpm). That means that over 60 percent of the people in the same age group have an HRM within 24 bpm of one another, and 95 percent of them are within 48 bpm. That means that over half of the forty-five-year-olds, for example, will actually have a maximum heart rate that is anywhere from 163 to 187, but they will all base their training on a maximum heart rate of 175. And almost all of these forty-five-year-olds will actually have heart rates of 151-199, but, again, they will all be doggedly training in zones based on an HRM of 175. This tells you that the mean value of the HRM for all the subjects of the same age is not precise enough to be used for individualized training intensity assessment.
Hooray for math!
Bottom line: it might be right for you, but probably not. And it could be off by quite a bit. So if it's important to you, find another way to calculate it. (That's too much to discuss in a "Quick Question.")
Be seeing you.