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.
How many calories does Zone 1 burn — per session and per day?
Zone 1 gets skipped in most zone breakdowns because it looks negligible next to the higher zones. It is the zone people actually spend the most time in, though, so it is worth doing the arithmetic properly.
At the baseline used in the table above, Zone 1 runs at roughly 5 kcal per minute. That works out to about 150 kcal for 30 minutes, 220 kcal for 45 minutes, and 300 kcal for an hour of easy movement.
The catch: that figure includes calories you would have burned anyway
Heart-rate formulas report gross energy expenditure — the total your body used during the session, including the baseline metabolism that was running regardless. Someone of this size burns roughly 1 kcal per minute at rest, or about 1,400 kcal across a day just staying alive.
So the honest net figure — the calories Zone 1 added on top of doing nothing — is closer to 4 kcal per minute:
- 30 minutes: ~150 kcal gross, ~120 kcal net
- 45 minutes: ~220 kcal gross, ~175 kcal net
- 60 minutes: ~300 kcal gross, ~240 kcal net
The gap is small in the higher zones, where baseline metabolism is a rounding error against 11 or 13 kcal per minute. In Zone 1 it is roughly a fifth of the total, which is why Zone 1 sessions consistently feel like they should have "counted" for more than a calorie tracker gives them credit for.
"Per day" usually means one of two different things
People asking what Zone 1 burns per day are normally asking one of two questions, and the answers are very different:
- A daily easy session. A deliberate 30–60 minute walk or recovery ride: roughly 120–240 kcal of genuine additional burn per day, using the net figures above. Modest, but it accumulates to something meaningful across a week — and unlike hard sessions it adds almost no recovery cost.
- Total daily Zone 1 minutes logged by a watch. This is where the numbers get misleading. Watches often report several hours a day in Zone 1 because ordinary activity — walking around the house, cooking, commuting — sits in that heart-rate band. Multiplying those hours by 5 kcal per minute produces a wildly inflated figure, because almost all of it is your resting metabolism being counted as exercise.
Why the formula gets shaky at the bottom of Zone 1
There is a second reason to distrust whole-day Zone 1 totals. The Keytel equations behind these estimates were derived from steady-state exercise testing and are most reliable roughly between 90 and 150 bpm. Zone 1 starts at about 93 bpm at this baseline, meaning it sits at the very bottom edge of the validated range — and much of the time a watch labels "Zone 1" across a normal day falls below it entirely, where the regression was never fitted and can return implausible values.
The practical rule: use the per-session net figures for deliberate easy sessions, and treat any all-day Zone 1 calorie total as background noise rather than a number to plan a deficit around. If you want to set the intensity ceiling for those sessions properly, the active recovery heart rate calculator gives you the Zone 1 range for your age.
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.