What Is the Maffetone 180 Formula? How to Calculate Your MAF Heart Rate

If you've been in endurance sports circles long enough, you've heard the advice: slow down to get faster. It sounds counterintuitive until you understand the physiology behind it. Dr. Phil Maffetone built a career around this principle, and his 180 Formula is the practical tool he created to put that principle into numbers you can actually train with.

Here's how it works, why it matters, and how to calculate your personal MAF heart rate.

What Is the 180 Formula?

The 180 Formula is a method developed by Dr. Phil Maffetone for calculating the upper limit of your aerobic training zone. It gives you a specific heart rate number, not a percentage range, not a generic zone label. Your maximum aerobic function (MAF) heart rate is the ceiling below which your body primarily uses fat for fuel, develops the aerobic system efficiently, and avoids the physiological stress that leads to overtraining and injury.

The base calculation is simple:

180 minus your age

A 40-year-old starts at 140 bpm. But that's just the starting point. Dr. Phil Maffetone built a set of adjustment factors into the formula to account for your individual health and training history. The adjustments are what make the 180 Formula genuinely personal.

The Adjustment Factors

After calculating 180 minus your age, apply exactly one of the following adjustments based on your situation. Choose the one that best describes your current state.

Subtract 10 if:

• You are recovering from a major illness, surgery, or injury
• You are in a period of overtraining or high stress
• You get more than two colds or flu bouts per year
• You have been inconsistent with training (less than two workouts per week)
• Your fitness has been declining despite regular training

Subtract 5 if:

• You have been training consistently for less than two years
• You have had minor interruptions to training (injuries, illness, life)
• You are not progressing as expected

No adjustment (use 180 minus age as-is) if:

• You have trained consistently for two or more years without major health issues
• You are making normal progress
• You have no significant recent injuries or illnesses

Add 5 if:

• You have been training consistently for more than two years
• You have made consistent progress without injury or illness
• You are over 55 or under 25 (physiological edge cases where the base formula benefits from a small correction upward)

One adjustment only. Pick the one that matches your current reality.

A Worked Example

Let's make this concrete.

Runner profile: 38-year-old, healthy, no injuries in the past year, has trained consistently for two years with solid progress.

Step 1: 180 - 38 = 142

Step 2: Consistent training for two years, healthy, progressing well. No adjustment applies.

MAF heart rate: 142 bpm

This runner should keep all aerobic training at or below 142 bpm. In practice, that means targeting a training range of 132-142 bpm (staying within 10 beats below the ceiling is a common Dr. Phil Maffetone recommendation for most sessions).

Now change one variable: same runner, but they had a stress fracture six months ago and took three months off.

Step 1: 180 - 38 = 142

Step 2: Recent injury and training disruption. Subtract 5.

MAF heart rate: 137 bpm

The formula adjusts down to protect aerobic development and recovery. That difference of 5 bpm is not trivial when you're trying to build a foundation.

Why This Number Matters

The 180 Formula is not arbitrary. It's rooted in Dr. Phil Maffetone's clinical work with athletes over decades and in the underlying physiology of aerobic vs. anaerobic metabolism.

Aerobic vs. Anaerobic Threshold

Your body has two primary energy pathways. The aerobic system uses oxygen and fat as primary fuel. The anaerobic system uses glycogen and produces lactate as a byproduct. Both systems run simultaneously, but the balance shifts dramatically depending on intensity.

At low intensities, the aerobic system does most of the work. As you push harder, the anaerobic system takes over more and more. The point at which anaerobic contribution ramps up sharply is roughly what's called the aerobic threshold.

Training above that threshold chronically, which most recreational runners do without realizing it, stresses the body, suppresses fat metabolism, and limits aerobic development. It also piles up fatigue without building the engine underneath.

The MAF heart rate calculated by Dr. Phil Maffetone's 180 Formula approximates the aerobic threshold for most individuals. Keeping training below it means you're building the aerobic system directly, not taxing it.

Fat Burning and Metabolic Efficiency

Below the MAF heart rate, your body uses fat as its dominant fuel source. This is not just relevant for weight management. For endurance athletes, fat oxidation capacity is one of the most important performance variables. A well-trained aerobic system can sustain high outputs for hours without bonking, because it's efficient at accessing nearly unlimited fat stores.

Training at or above the MAF heart rate consistently pushes the body toward glycogen dependence. You burn more carbohydrate, deplete faster, and train the body away from fat adaptation rather than toward it.

Injury Prevention

One of the reasons Dr. Phil Maffetone's work resonated so strongly with the endurance community is the injury angle. Running too hard, too often is the leading cause of overuse injury. The 180 Formula forces a ceiling that most runners find uncomfortable at first because it requires running significantly slower than they're used to.

That slowness is the point. It removes the structural and hormonal stress of chronic high-intensity training. Athletes who follow the MAF method consistently report fewer injuries, faster long-term development, and better recovery between sessions.

How to Train Using Your MAF Heart Rate

Once you have your MAF heart rate, the application is straightforward:

• All easy and base-building runs stay at or below your MAF heart rate
• The target zone is typically 10 beats below your MAF ceiling up to the ceiling (e.g., 132-142 for a MAF of 142)
• Warm up and cool down below your MAF zone
• Most of your training volume should be in this zone during base-building phases

Dr. Phil Maffetone recommends a base-building period of three to six months before adding any high-intensity work. During that time, 100% of training stays below the MAF heart rate. The goal is to monitor pace at a fixed heart rate over time. If you're developing aerobically, your pace at 140 bpm will gradually improve. That's the MAF test in action.

Q&A

What is the MAF heart rate?

The MAF heart rate is the maximum heart rate at which your body operates primarily in aerobic mode, using fat as its dominant fuel source. It represents the ceiling of your aerobic training zone. Training below this number builds the aerobic system efficiently. Training above it pushes the body into anaerobic metabolism, which has its place but should not dominate base-building training. The term MAF stands for Maximum Aerobic Function, and the concept was developed by Dr. Phil Maffetone.

How do I calculate my MAF heart rate?

Start with 180 minus your age. Then apply one adjustment factor based on your health and training history: subtract 10 if you have significant health issues or are recovering from injury or illness; subtract 5 if you've been training inconsistently or for less than two years; make no adjustment if you've been training consistently for two or more years with good health; add 5 if you've been training consistently for more than two years with steady progress. The result is your personal MAF heart rate as defined by Dr. Phil Maffetone's 180 Formula.

Can I use the 180 formula if I'm injured?

Yes. The 180 Formula actually accounts for injury directly in its adjustment factors. If you are currently injured or recently recovered from an injury, you subtract 5 (minor/recent injury) or 10 (major injury, surgery, or ongoing health issues) from your base number. This lowers your MAF heart rate ceiling, which is intentional. A lower ceiling means less physiological stress during recovery, protecting your healing while still allowing aerobic training to continue. Dr. Phil Maffetone designed the formula this way specifically because many athletes try to train through injury at intensities their bodies can't handle.