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What Is Target Heart Rate?

Your target heart rate (THR) is the heart rate range you aim to sustain during exercise to achieve a specific training effect. It is expressed as a percentage of your maximum heart rate (MHR) — the theoretical highest number of times your heart can beat per minute.

Training at different percentages of your MHR produces different physiological adaptations: fat oxidation, aerobic base development, lactate threshold improvement, or maximal cardiovascular output. Ignoring zones means leaving adaptation on the table — or overtraining into fatigue and injury.

Skip the math: our target heart rate calculator gives you all five zones instantly from your age and resting heart rate.

"Most recreational athletes spend 80% of their time in zones that are too hard for recovery and too easy for peak performance. Heart rate zones fix this."

Maximum Heart Rate Formula

The simplest and most widely used formula is:

220 − Age (Fox formula, 1971) — Standard in most apps and devices. Underestimates MHR for fit individuals, overestimates for sedentary older adults. Standard deviation is ±10–12 bpm.
208 − (0.7 × Age) (Tanaka formula, 2001) — More accurate across a broader age range, especially for adults over 40. Meta-analysis validated on 351 studies.
211 − (0.64 × Age) (Gellish formula, 2007) — Preferred in clinical and research settings. Accounts for training status better than Fox.

Example: A 35-year-old using Fox: 220 − 35 = 185 bpm. Using Tanaka: 208 − (0.7 × 35) = 183.5 bpm. The Tanaka value is typically more accurate. Our calculator uses the Tanaka formula by default.

Heart rate zone chart showing five training zones as percentages of maximum heart rate

The Five Heart Rate Training Zones

Zone	% of Max HR	Feel	Primary Benefit
Zone 1 — Recovery	50–60%	Very easy, conversational	Active recovery, warm-up
Zone 2 — Base Aerobic	60–70%	Easy, can hold a conversation	Fat oxidation, aerobic base
Zone 3 — Aerobic	70–80%	Moderate, short sentences	Aerobic efficiency
Zone 4 — Threshold	80–90%	Hard, words only	Lactate threshold, race pace
Zone 5 — Maximum	90–100%	Max effort, unsustainable	VO2 max, peak power

For a 35-year-old with estimated MHR of 184 bpm: Zone 2 = 110–129 bpm, Zone 4 = 147–166 bpm, Zone 5 = 166–184 bpm.

Zone 2 Training: Why It Matters Most

Zone 2 (60–70% MHR) is the most researched and most overlooked training zone. Elite endurance athletes spend 75–80% of their training volume here. Here is why:

Maximal fat oxidation: At 60–70% MHR, the body preferentially burns fat as the primary fuel. Higher intensities shift fuel use toward glucose. Zone 2 builds the metabolic machinery to oxidize fat efficiently.
Mitochondrial development: Zone 2 is the primary stimulus for mitochondrial biogenesis — creating new mitochondria and increasing existing mitochondrial density. More mitochondria = more aerobic capacity.
Low systemic stress: Zone 2 can be performed daily without accumulating fatigue. It builds aerobic base without the recovery demand of threshold or interval work.
Cardiovascular health: Sustained Zone 2 work is the most evidence-backed intensity for reducing cardiovascular disease risk, improving insulin sensitivity, and lowering resting heart rate over time.

Track calories burned in each zone with our calories burned calculator. Pair with our pace calculator if you run to find the pace that keeps you in Zone 2.

Calories Burned by Heart Rate Zone

Calorie burn rate correlates with exercise intensity. Higher zones burn more calories per minute but cannot be sustained as long. Zone 2 burns fewer calories per minute but can be sustained for 60–120+ minutes, producing high total calorie expenditure.

Zone	Cal/Min (70 kg person)	Fuel Source	Sustainable Duration
Zone 1	4–6 cal/min	~70% fat	Hours
Zone 2	6–9 cal/min	~65% fat	60–120+ min
Zone 3	9–12 cal/min	~50% fat / 50% carb	30–60 min
Zone 4	12–16 cal/min	~80% carb	20–40 min
Zone 5	16–20+ cal/min	~90%+ carb	30–120 sec bursts

How to Measure Heart Rate During Exercise

Chest strap (most accurate): Uses electrical signals from the heart. Accuracy within 1–2 bpm. Best for high-intensity training where wrist-based devices fail. Polar H10 is the gold standard.
Wrist-based optical (convenient): Most smartwatches (Apple Watch, Garmin, Fitbit) use photoplethysmography (PPG). Accurate in Zones 1–3; degrades at high cadence or intensity due to motion artifact. ±5–10 bpm error common at Zone 4–5.
Manual palpation: Count pulse at neck or wrist for 15 seconds, multiply by 4. Accurate but only useful for steady-state checks — impractical during high-intensity work.
Talk test: Zone 2 is the highest intensity at which you can hold a full conversation without breaking sentences. Simple, no equipment, surprisingly reliable.

Common Heart Rate Training Mistakes

Training in "grey zone" (Zone 3) constantly

Zone 3 is too hard for full recovery and too easy for maximal performance gains. Most recreational athletes live here. Evidence-based endurance training is polarized: mostly Zone 2 with some Zone 4–5 work.

Using Fox (220 − Age) without adjustment

The Fox formula has a standard deviation of ±10–12 bpm. Two people of the same age can have true MHRs 20+ bpm apart. Use Tanaka or Gellish for better estimates, or test directly with a maximal effort protocol.

Ignoring resting heart rate

Resting heart rate (RHR) improves as aerobic fitness increases — trained endurance athletes often have RHR of 40–50 bpm. If your RHR increases week-over-week, it signals overtraining or illness before other symptoms appear.

Applying the same zones to all exercises

Heart rate zones are exercise-specific. Cycling HR typically runs 10–15 bpm lower than running HR at the same perceived effort due to differences in muscle mass recruited. Calibrate zones per activity.

Heart Rate FAQs

What is the fat burning heart rate zone?

Zone 2 (60–70% of max HR) is often called the "fat burning zone" because fat contributes the largest percentage of fuel at this intensity. However, total fat calories burned depends on duration — 90 minutes in Zone 2 burns more fat than 30 minutes in Zone 4, even though Zone 4 burns a higher percentage from fat per minute.

What is a good resting heart rate?

For adults, 60–100 bpm is considered normal by the American Heart Association. Athletes often have resting heart rates of 40–60 bpm. Values below 40 in non-athletes may warrant medical evaluation.

How long should I stay in Zone 2?

Research supports 45–90 minutes per Zone 2 session for aerobic base development. Elite athletes do 2–3 hour sessions, but 45 minutes 3–5 days per week is effective for most people. The key is consistency over months, not weeks.

Can I do Zone 2 training every day?

Yes. Zone 2 is low enough in intensity that it does not accumulate fatigue the way Zone 4–5 work does. Many programs prescribe daily Zone 2 walks or easy runs. The main constraint is time, not recovery.

Target Heart Rate Calculator Guide: Train in the Right Zone