If you've ever glanced at a fitness watch mid-run and wondered whether 150 bpm is "good," heart rate zones are the answer. They turn a raw number into a simple question: how hard am I actually working right now?
Step 1: Estimate your max heart rate
Everything starts with your maximum heart rate — the fastest your heart can beat during all-out effort. The classic estimate is:
Max heart rate = 220 − age
So a 40-year-old has an estimated max of 180 bpm. It's an average across lots of people, so your true max could be 10 or more beats different — but it's a solid starting point.
Step 2: Split it into five zones
Zones are percentage ranges of that max:
- Zone 1 · Very light (50–60%) — warm-ups, cool-downs, easy walks
- Zone 2 · Light (60–70%) — relaxed pace; you can hold a full conversation
- Zone 3 · Moderate (70–80%) — steady effort; breathing gets heavier
- Zone 4 · Hard (80–90%) — threshold work; only short sentences
- Zone 5 · Maximum (90–100%) — sprints you can hold for seconds, not minutes
For our 40-year-old, Zone 2 lands at about 108–126 bpm.
A more personal version: the Karvonen method
Two people of the same age can have very different fitness. The Karvonen formula accounts for that by using your resting heart rate:
Target = (max − resting) × intensity + resting
With a max of 180 and a resting rate of 60, Zone 2 becomes (120 × 0.6) + 60 = 132 up to (120 × 0.7) + 60 = 144 bpm — noticeably higher than the simple version, and usually a better fit for people who exercise regularly.
Why Zone 2 gets so much attention
Much of an endurance athlete's training happens in Zone 2. It builds your aerobic base — more efficient heart, better fat burning, more endurance — while being easy enough to recover from quickly. A common approach is roughly 80% of training at easy intensity and 20% hard.
How to use it
The Heart Rate Zone Calculator gives you all five zones in beats per minute. Enter your age for the standard method, or add your resting heart rate (measured first thing in the morning) to switch to Karvonen zones automatically.
Some tips for putting the zones to work:
- Slow down on easy days. Most people run their "easy" runs too fast, drifting into Zone 3.
- Give hard days a purpose. Short Zone 4–5 intervals, then full recovery.
- Watch the trend. A dropping resting heart rate over months is a great sign of improving fitness.
Pair your zones with the Running Pace Calculator to plan paces for each effort, or check the Calorie (TDEE) Calculator to fuel your training properly.
These zones are general estimates and not medical advice. If you take heart medication or have a heart condition, talk to your doctor before starting intense exercise.