How to Calculate Zone 2 Heart Rate (Fat-Burn Zone)

Six weeks before the marathon, your friend the club runner hits you with the most offensive sentence in training: "You need to go slower." Every run feels too easy, like a warm-up that never ends. Meanwhile the faster runner beside you is out-sprinting you on your easy days and running circles around your hard ones.

Making peace with "too easy" is the gateway to everything endurance training can give you — and the zone that legitimises it is Zone 2. This is the gentle, conversation-pace band of effort that does the unglamorous work: building the aerobic engine that everything else in running, cycling, and rowing stands on top of. Here's how to find your personal Zone 2, why it's mislabelled, and why it deserves to be the biggest slice of your training pie.

What Zone 2 actually is

Zone 2 is a band of intensity around 60–70% of your maximum heart rate — firmly aerobic, comfortably sustainable, and famously "conversational." Your body works entirely within its oxygen supply: fat is a major fuel source, waste products clear as fast as they form, and you could keep this effort up for hours without going into serious debt.

That last property — it's a sustainable zone — is its real superpower. Because it's easy enough to repeat, you can accumulate far more volume in Zone 2 than anywhere else, and that volume is what builds mitochondria, capillaries, and the oxidative machinery that define a durable endurance base. The hard sessions sharpen the needle; Zone 2 makes the engine bigger.

Method 1 — percentage of max heart rate (simple)

Max HR = 220 − age
Zone 2 = 0.60 × max HR  to  0.70 × max HR

A 35-year-old:

Max HR = 220 − 35 = 185
Zone 2 = 111–130 bpm

That's quick, universal, and blunt. It inherits the fuzziness of 220 − age — real max heart rate varies by roughly ±20 beats per minute at any age — and it ignores your fitness level entirely.

Method 2 — Karvonen: heart-rate reserve (more personal)

The Karvonen formula, named for the Finnish physiologist Martti Karvonen who introduced the method in the 1950s, accounts for your resting heart rate — and therefore your fitness. It computes your reserve (the gap between your resting rate and your max) and takes the zone as a percentage of that gap, added back onto rest:

HRR = max HR − resting HR
Zone 2 = (0.60 × HRR + resting HR)  to  (0.70 × HRR + resting HR)

Worked example — same 35-year-old, resting HR 60:

HRR = 185 − 60 = 125
Lower = 0.60 × 125 + 60 = 135
Upper = 0.70 × 125 + 60 = 148
Zone 2 = 135–148 bpm

Notice what happened: the personal number (135–148) sits well above the blanket one (111–130). That's not a contradiction — it's the reserve method doing its job. A fitter person has a lower resting heart rate, which lifts their Zone 2 into higher absolute beats. Training zones are percentages of your possibility range, not of a crowd average. Two people with the same age can genuinely have non-overlapping Zone 2 brackets.

The "fat-burn zone" label, decoded

If your gym screen calls this the "fat-burn zone," it's half a myth wearing marketing clothes. It's true that at lower intensities a higher proportion of calories come from fat. But total fat burned is driven mostly by total calories and total training volume — and a Zone 2 session can't be shortchanged as a fat-burning day; it's an aerobic build day whose fuel choice happens to favour fat. Called up for training and not for stoking the treadmill's timer, Zone 2 is compulsory; called up as a weight-loss hack, it's just one tool among many.

How to actually train in it — in practice

A few checks that beat fiddling with a formula:

• The talk test. At Zone 2 you should hold a conversation in full sentences. Feeling puffed and snippet-y? Nose back off.
• The perceived-effort check. Around a 3–4 on a 10-point effort scale — "easy but purposeful," not "barely doing anything."
• The nose-breath cue. Many people can comfortably nose-breathe all day in Zone 2. It's a rough but handy boundary marker.

If your watch keeps nagging you to slow down for weeks on end, that's not an equipment malfunction — it's the training working. The faster versions of you appear later, specifically because the base was built first. Ease off if you can't hold Zone 2's conversational pace, and don't be shy about dropping to walking on hills.

Key takeaways

• Zone 2 ≈ 60–70% of max HR, or the equivalent slice of your heart-rate reserve via the Karvonen formula.
• The percentage method is simple but blunt; Karvonen personalises the range using your resting heart rate.
• Zone 2's value is volume and sustainability — it builds the aerobic base that hard sessions refine.
• "Fat-burn" is a simplification; train Zone 2 for endurance, and pair it with occasional harder efforts for the complete stimulus.

FAQ

Can I do all my training in Zone 2? You can build a formidable base that way, and many beginners and volume-focused athletes effectively do. But athletes chasing top performance usually add sessions of harder effort, since the highest intensities raise the ceiling of the engine that Zone 2 grows in size.

Why does my Zone 2 feel so slow? Because that's what easy training is. Impulse wants every session to be a hard one; adaptive physiology wants most sessions easy so the hard ones can be properly hard. Trust the process for a season before judging it.

My resting heart rate keeps falling — is my Zone 2 changing? Yes, and that's the intended signal. Since Karvonen builds your range from your reserve, a lower resting pulse shifts your Zone 2 upward. Recalculate your range whenever your resting heart rate drops by a few beats — it means the training is landing.

Get your exact, personalised range with the Zone 2 Heart Rate Calculator, and double-check the max-heart-rate foundation with the Max Heart Rate Calculator so both methods start from the same ceiling.