Heart Rate Zones Calculator

What heart rate zones do

Training in different heart rate ranges trains different physiological systems. Hitting the right zone for your goal is more efficient than just “going hard.”

The five-zone model (used by most coaches and all major fitness watches):

Zone	% HRmax	Effort	Adaptation
Zone 1	50–60%	Very easy, can talk easily	Recovery, capillarization
Zone 2	60–70%	Easy, conversational	Aerobic base, fat oxidation, mitochondrial density
Zone 3	70–80%	Moderate, broken sentences	Aerobic capacity, but high recovery cost
Zone 4	80–90%	Hard, only 1–2 word answers	Lactate threshold, race pace
Zone 5	90–100%	Maximal, no talking	VO2max, neuromuscular power

Zone 2 is where most of your aerobic adaptations happen with the lowest recovery cost. It’s the zone you “don’t feel” you’re training but accumulates the most useful low-cost volume. Zone 4–5 work, in smaller doses, drives the top-end fitness improvements.

The three formulas

220 minus age (Fox, 1971)

HRmax = 220 − age

The classic. Easy to compute, widely cited. Originally a rough estimate published by Fox, Naughton, and Haskell in 1971. Reasonably accurate for adults 20–40, but systematically underestimates HRmax for older adults by 5–15 bpm.

Tanaka (2001)

HRmax = 208 − 0.7 × age

Tanaka, Monahan, and Seals (2001) published this revised formula based on a meta-analysis of 351 studies and a validation study in 514 healthy individuals. It’s more accurate than 220-age, especially for adults over 40.

For a 30-year-old, the two formulas give nearly identical results (220−30 = 190; 208−21 = 187). For a 60-year-old, Tanaka (166 bpm) is meaningfully higher than Fox (160 bpm).

Karvonen (heart rate reserve)

Target = ((HRmax − HRrest) × intensity%) + HRrest

The Karvonen formula uses heart rate reserve instead of HRmax directly. You feed in your resting heart rate (HRrest) along with HRmax, and the zones are calculated from the dynamic range between them.

Why it’s more personal: a 30-year-old elite endurance athlete might have HRrest = 40 bpm and HRmax = 195 bpm — a heart rate reserve of 155 bpm. A sedentary 30-year-old might have HRrest = 75 bpm and HRmax = 195 bpm — a reserve of only 120 bpm. At “70% intensity”:

• Athlete: (155 × 0.70) + 40 = 148.5 bpm
• Sedentary adult: (120 × 0.70) + 75 = 159 bpm

Same age, same HRmax, completely different target heart rates because their fitness levels differ.

A worked example

A 40-year-old, resting heart rate 65 bpm:

• Fox: HRmax = 220 − 40 = 180 bpm
• Tanaka: HRmax = 208 − 28 = 180 bpm (very close at 40)

Zones from Tanaka:

Zone	% HRmax	Range (bpm)
Z1	50–60%	90 – 108
Z2	60–70%	108 – 126
Z3	70–80%	126 – 144
Z4	80–90%	144 – 162
Z5	90–100%	162 – 180

Karvonen zones (using HRmax = 180, HRrest = 65, HRR = 115):

Zone	% HRR	Range (bpm)
Z1	50–60%	122 – 134
Z2	60–70%	134 – 145
Z3	70–80%	145 – 157
Z4	80–90%	157 – 168
Z5	90–100%	168 – 180

Notice that Karvonen Zone 2 (134–145 bpm) is meaningfully higher than HRmax-based Zone 2 (108–126 bpm). Karvonen accounts for the fact that this person’s heart starts at 65 bpm, not 0 bpm. For a fit individual, Karvonen produces more realistic targets.

How to use this calculator

1. Enter your age.
2. Optionally enter your resting heart rate to enable Karvonen mode.
3. Pick your HRmax method: 220-age (Fox) or Tanaka.
4. Read your five zones in beats per minute.

Where to spend your training time

For a typical recreational athlete training 3–6 hours per week:

• 70–80% in Zone 2. Builds the aerobic base. Easy on recovery.
• 10–20% in Zone 4–5. Drives VO2max. Smaller doses; 2–3 sessions per week max.
• 5–10% in Zone 3. Tempo work. Useful but easy to over-do; the “junk miles” risk.
• 5–10% in Zone 1. Active recovery, warm-up, cool-down.

This is the 80/20 polarized training model, originally championed for endurance athletes by Stephen Seiler. It applies surprisingly well to recreational mixed-modal training too.

When heart rate zones mislead

• First two weeks of training. Heart rate runs higher than effort would suggest because the cardiovascular system isn’t adapted yet.
• In heat. Heart rate drifts up at the same effort. A Zone 2 effort in 20°C is a Zone 3 reading in 30°C. Use rating of perceived exertion (RPE) as a cross-check.
• Dehydrated. Same drift pattern.
• Caffeinated. Heart rate runs 5–15 bpm higher with caffeine.
• After alcohol. Heart rate runs higher at any given effort.
• During strength training. Heart rate zones don’t apply to lifting. Strength sessions use rep ranges and load percentages instead.

Pairing heart rate with RPE and pace

A robust training feedback loop uses three signals together:

1. Heart rate — what your cardiovascular system is doing.
2. Pace or power — what work you’re actually producing.
3. RPE (1–10 scale) — how hard the effort feels.

When all three agree, you’re well-calibrated. When they disagree (e.g., low heart rate, easy RPE, but slow pace), something is off — fatigue, dehydration, illness coming on, equipment problem.

For most lifters who want a simple “should I do this conditioning session?” check: train in Zone 2 by feel, glance at heart rate to verify, and don’t overthink it.