Training by heart rate zones is the simplest way to control cardio intensity without relying on feel alone. The Karvonen formula is the most widely used method to set those zones because it accounts for both your maximum and your resting heart rate — and that tailors the training to each person’s fitness.
If you just want the numbers, use our heart rate zone calculator. If you want to understand the math and how to apply it in sessions, read on.
The Karvonen formula
The calculation is:
Target HR = (max HR − resting HR) × intensity + resting HR
The gap between max and resting heart rate is your heart rate reserve. The intensity you want (say 70%) applies to that reserve, not to max heart rate on its own. That is why two people of the same age but different fitness get different zones: a better-trained heart usually has a lower resting rate.
Example. A 30-year-old with an estimated max HR of 187 bpm and a resting HR of 60 bpm, training at 70%:
(187 − 60) × 0.70 + 60 = 127 × 0.70 + 60 = ≈ 149 bpm.
How to estimate maximum heart rate
A supervised stress test is ideal. Without one, the most accepted estimate today is the Tanaka formula:
Max HR = 208 − 0.7 × age
It is more accurate than the classic 220 − age, which overestimates max HR in younger people and underestimates it in older ones. If you have a measured value (from a test or a heart rate monitor during real effort), use the measured value — it always beats any formula.
How to measure resting heart rate
Resting heart rate should be measured lying down, right after waking, before getting up. Count your beats for a full minute (or 30 seconds and multiply by two) over several days and use the average. Coffee, stress and poor sleep raise it — which is why a multi-day average is worth more than a single reading.
The 5 training zones
| Zone | Intensity | What it is for |
|---|---|---|
| Z1 — Recovery | 50–60% | Warm-up and active recovery |
| Z2 — Aerobic base | 60–70% | Endurance, comfortable long pace — the “fat-burning zone” |
| Z3 — Aerobic | 70–80% | Cardiorespiratory conditioning |
| Z4 — Threshold | 80–90% | Near the anaerobic threshold, hard effort |
| Z5 — Maximum | 90–100% | Short bursts and high-intensity intervals |
Does the “fat-burning zone” exist?
Partly. In Zone 2 the body does use a higher proportion of fat as fuel. But that does not make it the best zone for weight loss: higher zones burn more calories per minute, even at a lower share of fat. To plan the week, the usual approach is to combine plenty of Z2 volume with a few harder Z4/Z5 sessions. To estimate the burn of each session, see the cardio calorie calculator.
How to use the zones in practice
- Base runs and long runs: stay in Z2. That is where endurance is built without piling up fatigue.
- Intervals: alternate Z4/Z5 blocks with Z1/Z2 recovery.
- Beginners: spend most of the time in Z1/Z2; rushing into higher zones is the most common mistake.
- Prescribing for clients: log the target zone of each session and check whether the client hit it — zone control is what separates a running plan from a plain list of workouts.
In Fitney, the personal trainer builds the running and cardio plan with intensity zones, spreads it across the week and tracks the client’s progress from an app with their own brand. Try it free for 14 days, no card.
