Calories burned per zone: what the numbers look like
The table below shows estimated calorie burn per 45-minute session for a 35-year-old, 70 kg (154 lb) person using the Keytel formula — one of the most validated heart-rate-based calorie estimation methods available.
| Zone | % Max HR | Approx. HR | Cal/min | 45 min total |
|---|---|---|---|---|
| Zone 1 Recovery | 50–60% | ~93–111 bpm | ~5 | ~220 kcal |
| Zone 2 Aerobic Base | 60–70% | ~111–130 bpm | ~7 | ~315 kcal |
| Zone 3 Aerobic | 70–80% | ~130–148 bpm | ~9 | ~405 kcal |
| Zone 4 Threshold | 80–90% | ~148–167 bpm | ~11 | ~495 kcal |
| Zone 5 VO2 Max | 90–100% | ~167–185 bpm | ~13 | ~585 kcal |
These are estimates for one specific profile. Your numbers will be different based on your age, weight, sex, and fitness level. Use the calculator below for a personalised result.
Get your personal calorie burn based on your actual heart rate and workout data.
Calories Burned Calculator →Why higher zones burn more — but it's not the whole story
More intensity means more oxygen consumption, which means more energy (calories) burned per minute. This is straightforward physiology. But there are two important caveats that most people overlook.
1. Duration makes the difference
Zone 5 burns roughly 2.5× more calories per minute than Zone 1 — but you can't stay in Zone 5 for more than a few minutes before having to stop or drop intensity. A 45-minute Zone 2 session will almost always burn more total calories than a 10-minute Zone 5 effort, even though Zone 5's per-minute rate is higher.
2. Afterburn is real but often overstated
High-intensity exercise triggers excess post-exercise oxygen consumption (EPOC) — your body continues burning elevated calories for hours after the session. This is real. But research consistently shows EPOC adds roughly 6–15% on top of the calories burned during the workout itself — not the dramatic "48 hours of extra burn" sometimes advertised.
The practical bottom line
For pure calorie burn in a single session, higher zones win — if you can sustain them for the full duration. For total weekly calorie burn, Zone 2 often comes out ahead because it can be done more frequently and for longer without accumulating excessive fatigue.
Zone 2 and fat burning: what's actually happening
Zone 2 has a specific advantage that the calorie numbers above don't capture: at this intensity, your body preferentially uses fat as fuel rather than carbohydrates. This matters for two reasons.
First, you're drawing down fat stores directly during the workout. Second, consistent Zone 2 training improves your body's ability to oxidize fat at all intensities — meaning over weeks and months, you become more metabolically efficient at using fat even during higher-intensity exercise.
This is why endurance athletes and longevity researchers like Dr. Peter Attia emphasize Zone 2 heavily — not just for the calories burned in the session, but for the metabolic adaptations it drives over time.
Which zone should you train in for your goal?
For weight loss
Total weekly calorie deficit is what drives fat loss, not the zone you train in. A mix of Zone 2 (sustainable, high frequency) and Zone 3–4 (higher intensity, lower frequency) tends to produce the best overall calorie expenditure while remaining sustainable long-term.
For aerobic fitness and endurance
Zone 2 should make up the majority of your training — roughly 80% by volume. This builds your aerobic base, improves mitochondrial function, and creates the foundation that makes higher-intensity efforts more effective.
For cardiovascular health
Any consistent aerobic exercise in Zones 1–4 improves cardiovascular markers. Zone 2 is often the most sustainable entry point, especially for those returning to exercise or managing cardiovascular risk factors.