Run at or just below this number. It is a ceiling, not a target to hit every minute. Not a medical value: if you have a heart condition, ask your doctor first.
How the MAF 180 formula works
The short answer
Subtract your age from 180. Then adjust: minus 10 if you are recovering from a major illness or on regular medication, minus 5 if you are injured, regressing or often sick, plus 5 if you have trained for over two years without problems and are still improving. That number is the top of your aerobic range. Train between it and 10 beats below.
MAF stands for maximum aerobic function. Phil Maffetone built the formula in the 1970s and 1980s while working with endurance athletes, and published it in his books, including The Big Book of Endurance Training and Racing. The idea is simple: below this heart rate you are training almost only the aerobic system, which is what endurance is built on.
The formula is not derived from a lab test. It is a rule of thumb that Maffetone found worked across many athletes, and it deliberately lands on the cautious side. For most runners it gives a number close to the top of Zone 2, or a few beats below it.
MAF vs Zone 2
Our Zone 2 calculator uses the Karvonen formula, which includes your resting heart rate. MAF does not. So they can differ by a few beats either way. Neither is wrong. Both point to the same thing: easy running, slow enough to talk, done most of the week.
| Age 40 | MAF (no adjustment) | Zone 2 (resting HR 55) |
|---|---|---|
| Top of range | 140 bpm | about 145 bpm |
| Bottom of range | 130 bpm | about 132 bpm |
If the two disagree, run the lower number for a few weeks. If your pace at that heart rate gets faster over time, your aerobic base is growing. That is the test Maffetone uses too, the MAF test.
