Heart Rate Zones Explained: Karvonen Formula & the Fat-Burn Myth

Guides · Fitness · Updated 2026

Heart rate training turns your pulse into a dashboard — each zone targets a different energy system, from base endurance to max sprint. But the old "fat‑burning zone" advice (keep it low and slow) has been oversimplified to the point of being misleading. This guide explains the 5 zones, shows how to calculate them using the Karvonen formula (which factors in your resting heart rate), and reveals why total calories burned matters more than the percentage of fat used. Use our calculator to get your personal zones in seconds.

Why the "Fat‑Burning Zone" Is Misunderstood

At lower intensities (Zone 2), a higher percentage of energy comes from fat — perhaps 60%. But the total calorie burn per minute is low. At higher intensities (Zone 4), fat percentage may drop to 30%, but total calorie burn is so much higher that absolute fat burn per minute often exceeds Zone 2. The real takeaway: mix intensities across the week. Low‑intensity builds aerobic base; high‑intensity increases total calorie expenditure and cardiovascular fitness.

Zone 1 (50–60% HRR): Very light, recovery.
Zone 2 (60–70% HRR): Aerobic base, "conversational pace."
Zone 3 (70–80% HRR): Tempo, improving lactate threshold.
Zone 4 (80–90% HRR): Threshold, hard but sustainable for ~30 min.
Zone 5 (90–100% HRR): Max effort, anaerobic, intervals only.

Step-by-step: Find Your Personal Heart Rate Zones

Open the Heart Rate Zone Calculator tool.
Enter your age and measured resting heart rate (best taken first thing in the morning before getting up).
The tool calculates your maximum heart rate (220 - age) and heart rate reserve (HRR = max HR - resting HR).
It applies the Karvonen formula for each zone and displays the target BPM range for all 5 zones. You can use these numbers to set up a fitness watch or guide your workout effort.

💡 Tip: Don't rely on the "220 - age" formula if you're well‑trained; it underestimates max HR for fit individuals. If you know your true max HR from a stress test, use that instead.

Karvonen Formula with Worked Example

      Karvonen formula: Target HR = Resting HR + (HRR × intensity %)

      HRR = Max HR - Resting HR. Max HR = 220 - age.

      Example: 30‑year‑old, resting HR = 60 bpm.

      Max HR = 220 - 30 = 190 bpm. HRR = 190 - 60 = 130 bpm.

      Zone 2 (60-70%):

      Lower: 60 + (130 × 0.60) = 60 + 78 = 138 bpm

      Upper: 60 + (130 × 0.70) = 60 + 91 = 151 bpm

      So Zone 2 = 138–151 bpm.

Use the Running Pace Calculator to match these zones to actual speed and distance targets for a complete training plan.

Frequently Asked Questions

Is the fat‑burning zone useless then?

Not useless — it builds aerobic efficiency and is great for recovery. But for weight loss, total calories matter more. A mix of low and high intensity yields the best results.

How do I measure my resting heart rate accurately?

Wear a heart rate monitor overnight, or take your pulse for 60 seconds immediately upon waking before sitting up. Average over a few days for the best resting HR value.

Can I use heart rate zones for strength training?

Heart rate lags behind effort in lifting. Zones are best for steady‑state cardio and interval running/cycling, not for sets of squats.

What if my heart rate zones feel too easy?

Your actual max HR may be higher than predicted. Consider a lab test or a field test (e.g., 5K race) to get a real max, then recalculate.

Is it free and private?

Yes — the tool runs entirely in your browser, free, with no sign‑up and nothing uploaded to a server.

Try the Heart Rate Zone Calculator