Try Equation # 2. My measured (4 times) max HR is 173. # 2 gives 171.

Al

Simple Formulaic Estimation of the MHR Based on Age:
In general, this method will provide reasonable accuracy for about 80% of runners, but it should almost invariably be supplemented with an actual test. Typically, one of three simple formulas is used to estimate one's maximum heart rate.

Formula #1: The first formula involves simply subtracting your age from the number 220 (for men) or from 226 (for women). This method is preferred for beginning runners, those who have been leading a sedentary lifestyle. MarathonGuide.com Simple Heart Zones Calculator

Formula #2: The second formula is very similar, but is preferable for those who are already quite active. For this formula, simply subtract half of your age from the number 205.

Formula #3: The third formula runs along the same vein as the two preceding it. For men, subtract 80% of your age from the number 214. For women, subtract 70% of your age from the number 209.

All of these formulas provide approximations that are based on the standard curves representing the "normal" MHR's for any given age, and they get you close to your own MHR, but not close enough. The numbers you will get when you plug in your own age would best be used as a guide, as opposed to an accurate measure.