Heart Rate Zones Calculator

What this calculator does & how it works

This tool builds your personal training zones in two steps. First it estimates your maximum heart rate using the long-standing population formula HRmax = 220 − age (the Fox formula). Then it applies the Karvonen method, which is more individualized than a flat percentage of HRmax because it accounts for how fit you already are.

The Karvonen formula works from your heart rate reserve (HRR), the gap between your maximum and resting heart rates: target = (HRR × intensity%) + resting HR. A fitter person with a low resting heart rate gets a wider, more accurate range than the generic version. If you leave resting heart rate blank, the calculation falls back to a simple percentage of HRmax. The five-zone model used here is the convention popularized by training systems and described by, among others, the American Heart Association.

How to interpret your results

Each zone serves a different training purpose. Zone 1 (50–60%) is very light — warm-ups and recovery. Zone 2 (60–70%) is the comfortable, conversational base that builds aerobic endurance and is where many endurance athletes spend most of their time. Zone 3 (70–80%) is moderate aerobic work. Zone 4 (80–90%) is hard, anaerobic effort that raises your lactate threshold. Zone 5 (90–100%) is near-maximal and only sustainable for short bursts.

You don't need to train in every zone every day. A common, well-supported approach is to keep most sessions easy (Zones 1–2) and add a smaller amount of hard work (Zones 4–5). To estimate the energy side of your training, pair this with our steps-to-calories calculator.

How to measure your resting heart rate

For the most accurate zones, measure your resting heart rate properly: count your pulse for a full 60 seconds first thing in the morning, before you get out of bed, across several days, and average the results. Many wearables estimate it automatically. A typical adult resting heart rate falls between about 60 and 100 bpm, and regular endurance training tends to lower it.

Limitations and when to consult a professional

The 220 − age formula is a population average that can be off by 10–20 bpm for any given person, so every number here is an approximation. True maximum heart rate is best measured under supervision in a graded exercise test. Certain medications (notably beta-blockers) lower heart rate and make these zones invalid, and conditions affecting the heart can change safe training ranges entirely. If you have a heart condition, chest pain, dizziness on exertion, or have been sedentary, talk to a doctor before starting or intensifying exercise. Stop and seek care if you feel unwell during activity. Nothing here is medical advice.

A worked example

Take the default inputs — age 35, resting heart rate 60. Maximum heart rate estimates as 220 − 35 = 185 bpm, and heart-rate reserve (the room between resting and max) is 185 − 60 = 125 bpm. The Karvonen method sets each zone as a percentage of that reserve added back to your resting rate. So the boundary between easy and moderate effort — around 60% — lands at (125 × 0.60) + 60 = 135 bpm, and the hard-effort threshold near 80% sits at (125 × 0.80) + 60 = 160 bpm. The full five-zone spread for this person runs roughly: Zone 1 (recovery) 122–135, Zone 2 (endurance) 135–148, Zone 3 (tempo) 148–160, Zone 4 (threshold) 160–172, and Zone 5 (max) 172–185 bpm.

Here's why the resting-heart-rate input matters. A flat "percentage of max" method would give everyone of the same age identical zones. Karvonen personalizes them: a well-trained person with a resting rate of 45 has a larger reserve (140 bpm) than someone at 70 (115 bpm), so their zones stretch wider and sit higher. That's the whole reason this method is preferred for anyone whose fitness has moved away from average — it adapts to the body you actually have, not just your birth year.

How to train with the five zones

• Zone 1 — recovery. Very easy; you can hold a full conversation. Used for warm-ups, cool-downs, and active recovery between hard days.
• Zone 2 — endurance. Comfortable, sustainable, still conversational. This is where the bulk of most people's training should live — it builds the aerobic base that everything else rests on, and it's the zone most amateurs skip by going too hard.
• Zone 3 — tempo. "Comfortably hard"; talking gets choppy. Useful in moderation but easy to overuse.
• Zone 4 — threshold. Hard; only a few words at a time. Builds the ability to sustain higher speeds, used in interval blocks.
• Zone 5 — maximum. All-out, sustainable only briefly. Reserved for short intervals, and the zone to be most cautious with if you're new or have any risk factors.

A widely used pattern is to spend most training time in Zones 1–2 and only a small fraction in Zones 4–5 — the "mostly easy, occasionally very hard" distribution that endurance coaches favor over grinding in the middle every session.

Where a chest strap beats a wrist reading

The zones are only as trustworthy as the heart-rate data feeding them. Optical wrist sensors are convenient but lag and misread during quick efforts and intervals; a chest-strap monitor tracks the electrical signal directly and is markedly more accurate for zone training. If your watch shows you leaping two zones in a few seconds, that's usually a sensor artifact, not your heart. To improve the biggest input, resting heart rate, measure it first thing in the morning before getting up, across several days, and average it. Pair this tool with the steps-to-calories calculator to gauge everyday activity, and see our heart rate zones guide for how to fold zones into a weekly plan. These are educational estimates — anyone with cardiac risk factors should get a clinician's input before training hard.

Frequently asked questions