Heart rate zone calculator.
Enter your age — or a max heart rate you've measured — to get your five training zones in beats per minute, plus the 85% threshold that defines a Norwegian 4×4 interval.
Max HR estimated with the Tanaka formula (208 − 0.7 × age). It can differ from your true max by 10–20 bpm — enter a measured max for accurate zones. See how to find your max heart rate.
What the zones mean
- Zone 1 (50–60%) — Recovery. Very easy; warm-ups and cool-downs.
- Zone 2 (60–70%) — Aerobic base. Conversational; builds endurance and the aerobic engine.
- Zone 3 (70–80%) — Tempo.Moderately hard; “comfortably uncomfortable.”
- Zone 4 (80–90%) — Threshold. Hard; sustainable only for a while. The 85% line sits here.
- Zone 5 (90–100%) — VO₂max. Very hard; the home of 4×4 intervals.
For training, the two that matter most are Zone 2 and Zone 5: an easy aerobic base plus hard VO₂max work.
Frequently asked questions
- How do I calculate my heart rate zones?
First estimate your maximum heart rate (this calculator uses 208 − 0.7 × age, or your own measured max if you enter it), then take percentages of it: Zone 1 is 50–60%, Zone 2 60–70%, Zone 3 70–80%, Zone 4 80–90%, and Zone 5 90–100%.
- What heart rate is Zone 5?
Zone 5 is roughly 90–100% of your maximum heart rate — the VO₂max zone. The Norwegian 4×4's intervals sit at the top of Zone 4 into Zone 5, above the 85% threshold this calculator highlights.
- What's the 85% threshold?
85% of your maximum heart rate is the line a Norwegian 4×4 interval has to stay above to count as real VO₂max work. The calculator shows it as a separate figure because it's the number that matters most for interval training.
- Are these heart rate zones accurate?
They're as accurate as your max-heart-rate figure. The age formula is an estimate that can be off by 10–20 bpm, so for the most accurate zones, enter a max heart rate you've measured in a field or lab test.
Train at VO₂max.
Know your zones — now train the top one. Stellar Intervals counts each 4×4 interval only while you're above 85% of max.