Zone 2 training is a low-to-moderate aerobic effort where your body primarily burns fat for fuel and mitochondrial density increases — the physiological foundation of endurance performance. Finding your Zone 2 heart rate or power boundary is important because it differs by method: the MAF formula uses age alone, the Karvonen formula accounts for your resting HR fitness level, and the FTP percentage gives a metabolic anchor for cyclists. This calculator shows all four methods side-by-side so you can compare and choose.
Your Details
Measure first thing in the morning
Leave blank to use 220 − age estimate
Your functional threshold power
+5 if healthy & training consistently 2+ years · −5 if recovering or returning from injury
How to Use the Zone 2 Training Calculator
Zone 2 training is the aerobic foundation of every serious endurance programme — it develops the mitochondria and fat oxidation capacity that determine how fast you can race and how well you recover. But the exact heart rate or power boundary varies by the method you choose, and this Zone 2 training calculator shows all four at once so you can cross-reference them.
Step 1: Enter Your Age
Age is the only required field. It drives the MAF method (180 − age) and is used to estimate max HR if you haven't measured it. Enter your current age in years. Accurate age is critical because a 5-year error shifts the MAF ceiling by 5 bpm — a significant difference for low-intensity training.
Step 2: Enter Resting Heart Rate
Resting heart rate is used by the Karvonen formula to personalise your Zone 2 boundary. Measure it first thing in the morning before getting out of bed — lie still for 2 minutes and count beats for 60 seconds (or 15 seconds × 4). A typical value is 50-70 bpm for recreational athletes; well-trained endurance athletes often see 40-55 bpm.
Step 3: Add Max HR and FTP (optional)
If you know your true maximum heart rate from a field test (a hard hill repeat or 3km time trial), enter it. If left blank, the calculator estimates max HR as 220 minus your age — this is a population average and may be off by 10-15 bpm for individuals. Cyclists with a known FTP can also enter it to unlock the power-based Zone 2 range (56-75% of FTP), which integrates seamlessly with platform training plans.
Step 4: Adjust the MAF Modifier
Dr Phil Maffetone's original protocol allows ±5 bpm adjustment. Add 5 bpm if you have been training injury-free for 2+ years and are in good health. Subtract 5 bpm if you are returning from injury, illness, or have been inconsistent. Keep it at 0 if you are unsure.
Step 5: Read Your Results
The calculator displays each method as a colour-coded card showing the low and high boundary of Zone 2. A combined summary at the bottom shows the consensus overlap — the range where all active methods agree you are in Zone 2. Use this overlap as your most conservative target during Zone 2 workouts. Over time, as your aerobic fitness improves, your pace at a given heart rate will increase — a reliable indicator that Zone 2 training is working.
Which Method Is Best?
There is no single correct method. The MAF method is simple and conservative, making it ideal for beginners and those building base. The Karvonen method is more personalised and widely used by coaches. The % max HR method (60-70%) is backed by extensive research on aerobic intensity. The % FTP method is excellent for structured cycling training where power is the primary metric. Using all four and targeting the overlap gives you the most reliable Zone 2 boundary without expensive lactate testing.
FAQ
Is this Zone 2 calculator free?
Yes, completely free with no signup required. All calculations run locally in your browser and no personal data is ever sent to a server.
Is my data safe and private?
Yes, all calculations happen entirely in your browser. Your age, heart rate, and FTP values are never transmitted to any server or stored after you close the page.
What is Zone 2 training?
Zone 2 is a low-to-moderate aerobic intensity where your body primarily burns fat for fuel and you can still hold a conversation. It develops mitochondrial density and aerobic base, which is the foundation for all endurance performance. Elite athletes typically spend 70-80% of their total training volume in Zone 2.
Which Zone 2 calculation method should I use?
If you only know your age, use the MAF method (180 minus age) — it's simple and conservative. If you know your resting HR, the Karvonen method is more personalised because it factors in your heart rate reserve. If you have a max HR test result, the % Max HR method is reliable. If you're a cyclist with an FTP, use % FTP for power-based training.
What is the MAF method and why is it useful?
The MAF (Maximum Aerobic Function) method, developed by Dr Phil Maffetone, sets your Zone 2 ceiling at 180 minus your age in BPM. It's conservative by design, ensuring you stay fully aerobic. It's particularly popular with runners and triathletes building base fitness and can be adjusted by ±5 BPM based on your training history and health.
What is heart rate reserve and how does Karvonen use it?
Heart rate reserve (HRR) is the difference between your maximum heart rate and resting heart rate. The Karvonen formula applies a percentage of this reserve and adds it back to resting HR. This personalises your zones because a fit athlete with a low resting HR gets different absolute BPM targets than a less fit person with the same max HR.
Why do the four methods give different numbers?
Each method uses different inputs and makes different assumptions about physiology. The MAF method uses only age. The Karvonen formula uses resting and max HR to reflect cardiovascular fitness. The % max HR method is a simpler but well-studied approach. The % FTP method is metabolic rather than cardiovascular. In practice, the true Zone 2 boundary is best confirmed by a lactate threshold test, but the ranges shown here are reliable estimates for most athletes.
Can I use Zone 2 for running as well as cycling?
Yes. The heart rate methods (MAF, Karvonen, % max HR) apply to any aerobic sport — running, cycling, rowing, or swimming. The FTP-based power method is cycling-specific. For running, many athletes use pace as a proxy: Zone 2 typically corresponds to a pace 1-2 minutes per mile slower than your 10K race pace.