Every heart rate zone is defined as a percentage of your maximum heart rate. That makes HR max the single most important number in zone-based training — yet most people have never measured theirs accurately. Here's how to find it and use it.
What is maximum heart rate?
Maximum heart rate (HR max) is the highest number of times your heart can beat in one minute. It's largely genetic and declines with age. It's not a measure of fitness — a highly trained athlete and a complete beginner of the same age typically have very similar HR max values. What training changes is how efficiently you use your heart rate range.
The 220-minus-age formula
The most widely known formula: HR max = 220 − age.
A 40-year-old's estimated HR max: 180 bpm. Simple, fast, and a reasonable starting point.
The problem: the standard deviation of this formula is ±10–12 bpm. That's a big error. An individual aged 40 might have a true HR max anywhere from 165 to 195 bpm, all of which would fall within the normal distribution. If your zones are based on 180 bpm but your actual max is 168 bpm, every zone calculation is wrong.
Use 220−age to get started. If you're serious about zone training, verify it with a test.
Better formulas
Several other formulas improve on 220-minus-age:
- Tanaka formula: HR max = 208 − (0.7 × age). Better calibrated for older adults and generally more accurate in research settings.
- Gellish formula: HR max = 207 − (0.7 × age). Similar to Tanaka, used in several commercial platforms.
- Fox formula: 220 − age. The original, most widely used despite its limitations.
For a 40-year-old, Tanaka gives 180 bpm (same as Fox), but diverges more significantly at older ages. A 65-year-old gets 174 bpm from Fox and 162.5 bpm from Tanaka — a meaningful difference that will affect zone calculations.
How to test your actual HR max
The only way to find your true max is to actually reach it. Warning: maximal tests are physiologically demanding. Don't attempt one if you have cardiovascular conditions, haven't been exercising regularly, or are new to hard training. Consult a doctor if unsure.
Option 1: Progressive ramp test (treadmill or bike)
- Warm up 10–15 minutes at easy pace
- Increase intensity every 1–2 minutes until you genuinely cannot continue
- Note the highest HR you see at the end
- Cool down immediately
The highest reading in the final 30 seconds is a reliable HR max estimate. Some people find their true max is 5–10 bpm higher than they expect from formulas.
Option 2: All-out interval
- Warm up 15 minutes at easy effort
- Run or cycle hard for 3 minutes at near-maximum effort
- Rest 2–3 minutes
- Sprint all-out for 30–60 seconds
- Record peak HR during or immediately after the sprint
Setting your zones from HR max
Once you have your HR max, calculate each zone:
- Zone 1: 50–60% of HR max
- Zone 2: 60–70% of HR max
- Zone 3: 70–80% of HR max
- Zone 4: 80–90% of HR max
- Zone 5: 90–100% of HR max
Example for HR max of 185 bpm:
- Z1: 92–111 bpm
- Z2: 111–129 bpm
- Z3: 129–148 bpm
- Z4: 148–166 bpm
- Z5: 166–185 bpm
HR max changes over time
Maximum heart rate declines at roughly 1 bpm per year from your late 20s onwards. This means zones should be recalculated periodically. Fitness improvements don't change HR max — but they do raise the pace or power output you can sustain at any given zone, which is the whole point.
Recalculate your zones any time you notice your previous "Zone 2 pace" feels significantly easier, or if you're more than a year away from your last test.
Using HR max with Underdog
Underdog calculates your heart rate zones from the data in Apple Health, which includes Apple Watch's estimate of your HR max based on your workout history. Your zone time is automatically categorised and converted to weekly points. As your fitness improves and your zones shift, the points system adjusts accordingly — Zone 2 always means 60–70% of your current max, regardless of what number that is.