How the MAF formula works
Phil Maffetone's method starts with 180 minus your age, then adjusts that number based on your health and training history. The result is your maximum aerobic function (MAF) heart rate: the ceiling for aerobic base training. Your training range is the 10 beats under that ceiling. A 40-year-old with no adjustment gets a ceiling of 140 and trains between 130 and 140 bpm. The ceiling is a hard limit for the session, not an average to hover around; if your heart rate drifts over it on a climb or late in a run, you slow down or walk until it comes back.
The adjustment checklist matters more than the 180
The part of the formula most calculators skip is the reason it works at all. Maffetone's position is that your aerobic ceiling is not fixed by age alone: health status shifts it. Illness, injury, medication, and inconsistent training all suppress aerobic function, so the formula subtracts beats to keep training stress inside what a compromised system can absorb. Subtract 10 if you are recovering from major illness or surgery or take regular medication. Subtract 5 if you are injured, regressing, getting more than two colds or flu per year, dealing with allergies or asthma, training inconsistently, or just returning to it. Use the unadjusted number if you have been training consistently for up to two years without any of those problems. Add 5 only if you have trained for more than two years without any of them and are still improving.
Be honest here. The most common way runners break the MAF method is claiming the plus 5 they have not earned. If any item on the minus 5 list applies to you, it applies, even if you would rather it did not. If two categories seem to fit, take the lower one.
What training at MAF actually feels like
Slow. For most runners, the first weeks at MAF heart rate feel almost insultingly easy for the lungs and frustrating for the ego. You will likely run one to three minutes per mile slower than your usual easy pace, walk hills, and get passed. You should be able to breathe through your nose and speak in full paragraphs, not just sentences. That is the point: MAF is deliberately conservative compared with the lab-tested aerobic threshold of many runners. For injury-prone athletes and anyone returning from a layoff, that conservatism is a feature, because it makes it nearly impossible to overcook an easy day. For an experienced runner chasing performance, it is a real limitation, since your true aerobic threshold may sit meaningfully above your MAF number and some useful training lives in that gap.
A coach's honest take
There is nothing physiologically magic about 180 minus age. It is a heuristic, and like any age-based formula it will miss for some individuals. MAF works because it forces genuinely easy running on runners who have never actually done any, and it pairs the restriction with a built-in progress check: the MAF test. Run a fixed course, a track or a measured 3 to 5 miles, at your MAF heart rate once a month and record your pace. If the method is working, pace at the same heart rate improves month over month. That feedback loop, not the specific number, is what makes MAF a system rather than a slogan. If you want to compare MAF against percent-of-max and Karvonen ranges before committing, the Zone 2 heart rate calculator shows all three side by side.
Worked example: a healthy, consistent 40-year-old
Take a 40-year-old who has trained consistently for three years, stayed healthy, and is still setting personal bests. That earns the plus 5 adjustment: 180 minus 40 plus 5 gives a ceiling of 145, so the training range is 135 to 145 bpm. Easy runs, long runs, and recovery days all stay at or under 145. On the monthly MAF test, this runner might average 9:10 per mile in month one, 8:55 in month two, and 8:40 in month three, all at the same 145 bpm ceiling. Same heart rate, faster pace: that is aerobic fitness improving, measured without a lab.
Related tools and guides
The Zone 2 heart rate calculator compares MAF with percent-of-max and Karvonen methods, and the max heart rate calculator estimates the number those other methods depend on. For the reasoning behind method choice, read MAF vs Karvonen vs percent of max, why Zone 2 feels too slow, and how slow easy runs should be.
Frequently asked questions
Why is my MAF pace so slow?
Because your aerobic system is less developed than your legs. If you have trained mostly at moderate intensity, holding your heart rate under the MAF ceiling can mean running two or three minutes per mile slower than feels natural. That gap is the finding, not the flaw: it shows exactly how much aerobic fitness you have to gain. As your base builds, pace at the same heart rate improves and the gap closes.
Can I walk during MAF training?
Yes, and early on many runners have to. The ceiling is the rule, not the mode of travel. If running pushes you over your number, walk until your heart rate drops back into the range, then run again. Run-walk at MAF heart rate builds the same aerobic machinery as continuous running at MAF heart rate, and the walking portions shrink as you get fitter.
What is the difference between MAF and Zone 2?
They aim at the same thing, genuinely easy aerobic running, but draw the line differently. Zone 2 is usually defined as a percentage of max heart rate or heart rate reserve, so it scales with your physiology. MAF uses one formula, 180 minus age with a health adjustment, and lands conservative for many runners. For most people the two ranges overlap heavily. Pick one method, stay consistent, and compare them on the Zone 2 heart rate calculator if you want to see both.
How long until MAF training works?
Expect 8 to 12 weeks of consistent aerobic volume before your pace at MAF heart rate improves noticeably. The first few weeks often feel like going backward, which is why the monthly MAF test matters: it turns a vague feeling of slowness into a measurable trend. If pace at the same heart rate is not improving after three months, look at sleep, stress, fueling, and total volume before blaming the method.
What if I have to walk hills to stay under my MAF ceiling?
Then walk the hills. Heart rate does not care about terrain, and neither does the adaptation you are chasing. Hiking uphill at MAF heart rate is normal even for experienced trail and ultra runners. Crest the hill, let your heart rate settle, and resume running. Fighting to run every step of a climb at the cost of blowing through your ceiling defeats the purpose of the session.