This is an old school technique that has no background of science at all. What has kept this formula from being discarded is the fact that it is simple. The problem with this technique is that it assumes that you will loose around one heart beat per year, not at all true of many people. Top end heart beat rates do vary a lot from person to person, no matter what their fitness or age is.
If you really want to find out what your maximum heart rate is you are going to have to perform controlled tests in a laboratory environment. These tests, performed by trained experts in this field, involve you using a cardiovascular training machine, e.g. running machine or exercise bike. The intensity of your workout is increased every 15 seconds, in the space of a few minutes you will have reached your top heart rate.
More practical is to use a 'submax test'. Here you exercise at a sub maximum level, with the aid of specific formulas you can then predict your maximum heart rate. Although not quite as accurate as laboratory analysis, predictions usually fall within five beats of lab results. What is best is to perform 2-3 different submax tests, finding the result from the average of all of them.
An example of a submax test would be using a step machine you perform step ups and downs of 8-10 inches for 3 minutes without any breaks. At the end take your average heart rate, using a heart rate monitor. Subsequently add to this average value the correct estimate factor, decided by your fitness level, using the following formulas. What is essential for accuracy of the final result is that the movements and effort used in the exercise is as equal with each repetition as possible.
Formula:
Average heart rate in the last minute + Estimate factor = Estimate max heart rate
The American College of Sports Medicine states that people should exercise within their 'target zone', i.e. between 55-90% of their maximum heart rate. At this level you should be burning excess calories without causing injury problems through overexertion. The higher you manage to exercise at the more calories you will burn, remaining at this level for any period of time is very difficult.
One of the best ways to increase your ability to do exercise at the highest end of your hear rate is to do interval training. This is where you mix the activities or severity of your workout to keep changing from low to middle, to high heart rate levels, raising the level gradually.