The Target Heart Rate Zone Calculator computes five personalised training zones using the Karvonen method, which factors in resting heart rate for individualised intensity targets.
Why Generic Heart Rate Charts Mislead
Walk into most gyms and you will find a poster showing heart rate training zones based on simple percentages of a theoretical maximum heart rate. These charts typically use the "220 minus age" formula and apply flat percentage bands. The problem: they ignore individual fitness level entirely. Two 35-year-old runners — one with a resting heart rate of 50 bpm and another with 75 bpm — would receive identical zone recommendations despite having fundamentally different cardiovascular capacities.
The Karvonen method corrects this by using heart rate reserve (HRR) — the difference between maximum heart rate and resting heart rate — as the basis for zone calculation. A fitter individual with a lower resting heart rate has a larger HRR, which shifts their zone boundaries upward. This produces training targets that more accurately reflect the actual physiological intensity of the workout for that specific person.
How the Karvonen Formula Works
The Karvonen formula calculates target heart rate (THR) as follows:
THR = (HRR × intensity%) + resting HR
Where HRR = max HR − resting HR. This approach — published by Karvonen, Kentala, and Mustala in 1957 — has been the standard method for exercise prescription in clinical and sports settings for over six decades. Its enduring use reflects its simplicity and its meaningful improvement over flat percentage methods.
If you do not know your true maximum heart rate (measured during a graded exercise test or all-out effort), this calculator estimates it using the Tanaka formula: 208 − 0.7 × age. The Tanaka formula is preferred over the older Fox formula (220 − age) because it was derived from a meta-analysis of 351 studies and performs better across all age groups. For the most accurate zones, use a measured max HR from a max heart rate estimation using four validated formulas or a supervised lab test.
The Five Training Zones Explained
Each zone serves a distinct physiological purpose. Effective endurance training distributes effort across all five zones according to the goals and periodisation of the training programme.
Zone 1 — Recovery (50–60% HRR)
Very light effort. Breathing is easy and conversation is effortless. This zone is used for warm-up, cool-down, and active recovery between hard training days. The primary benefit is promoting blood flow to aid recovery without adding meaningful training stress. Recommended activities include easy walking, gentle cycling, and post-workout stretching with movement.
Zone 2 — Aerobic Base / Fat Burn (60–70% HRR)
Comfortable effort where you can hold a conversation in full sentences. Zone 2 develops the aerobic energy system, improves fat oxidation, and builds the endurance foundation that supports all higher-intensity work. Most endurance athletes should spend 70–80% of their total training time in this zone. This is the zone where mitochondrial density and capillary networks develop most efficiently.
Zone 3 — Aerobic / Tempo (70–80% HRR)
Moderate effort. Conversation becomes limited to shorter sentences. This zone improves aerobic capacity, stroke volume, and the ability to sustain moderate effort for extended periods. Tempo runs, steady-state cycling, and sustained swimming sets typically fall in this zone. Extended time in Zone 3 develops the "tempo pace" that many runners use as a benchmark for training progression.
Zone 4 — Threshold / VO2max (80–90% HRR)
Hard effort at or near lactate threshold. Speaking is limited to a few words at a time. This zone produces the strongest stimulus for VO2 max improvement and lactate threshold elevation. Typical workouts include interval training (4–6 intervals of 3–5 minutes), hill repeats, and race-pace work. Zone 4 training is potent but fatiguing — limit to 1–2 sessions per week with adequate recovery between.
Zone 5 — Anaerobic / Maximum (90–100% HRR)
Maximum effort sustainable only for short bursts (30 seconds to 2 minutes). This zone develops anaerobic power, neuromuscular coordination, and the ability to tolerate high lactate concentrations. Sprint intervals, Tabata protocols, and short race finishes utilise this zone. Zone 5 work carries the highest fatigue cost and injury risk — use sparingly and always after thorough warm-up.
Karvonen vs. Percentage-of-Max-HR: A Direct Comparison
Consider two runners, both age 35 (estimated max HR: 184 bpm). Runner A has a resting HR of 50 bpm. Runner B has a resting HR of 75 bpm.
| Zone | % of Max HR Method (both runners) | Karvonen — Runner A (RHR 50) | Karvonen — Runner B (RHR 75) |
|---|---|---|---|
| Zone 2 (60–70%) | 110–129 bpm | 130–144 bpm | 140–151 bpm |
| Zone 4 (80–90%) | 147–166 bpm | 157–171 bpm | 162–173 bpm |
The flat percentage method assigns identical zones to both runners. The Karvonen method differentiates them: Runner A's zones are wider (because a larger HRR provides more dynamic range), while Runner B's zones are higher relative to their max (because a higher resting HR means a smaller HRR must be distributed across the same percentage bands). This distinction matters for training prescription — prescribing Zone 2 at 110–129 bpm for Runner A would be too easy, falling mostly in their true recovery zone.
Zone Distribution for Common Training Goals
The proportion of time spent in each zone depends on your training goal and periodisation phase. These guidelines reflect the consensus of current endurance coaching literature.
| Goal | Zone 1–2 | Zone 3 | Zone 4–5 |
|---|---|---|---|
| General health / fat loss | 80–90% | 10–15% | 0–5% |
| Half-marathon / marathon | 75–80% | 10–15% | 10–15% |
| 5K / 10K performance | 70–75% | 10% | 15–20% |
| VO2 max improvement | 60–70% | 10% | 20–30% |
These distributions apply to weekly training volume, not individual sessions. A typical training week might include 3–4 easy Zone 2 sessions, one tempo session in Zone 3, and one interval session in Zones 4–5. This polarised approach — training mostly easy with focused hard sessions — produces superior adaptation compared to spending the majority of training in Zone 3 (the "grey zone" where effort is too hard for recovery but too easy for maximal stimulus).
Pair zone-based heart rate training with running pace targets for sessions where pace is the primary variable (such as tempo runs or race-pace intervals). For overall energy balance, daily energy needs for active individuals should account for the training volume distribution across these zones.
Glossary
Heart Rate Reserve (HRR)
The difference between maximum heart rate and resting heart rate: HRR = maxHR − restingHR. Heart rate reserve represents the usable range of heart rate for exercise and forms the basis of the Karvonen method for calculating personalised training zones. A larger HRR indicates greater cardiovascular fitness and provides a wider dynamic range for zone-based training.
Karvonen Method
An exercise intensity prescription method published by Finnish physiologist Martti Karvonen in 1957. The formula — THR = (HRR × intensity%) + restingHR — produces personalised heart rate targets by incorporating resting heart rate as a proxy for individual fitness level. It remains the standard method for heart rate-based exercise prescription in clinical and sports settings.
Lactate Threshold
The exercise intensity at which blood lactate concentration rises sharply above baseline — typically occurring at 75–90% of VO2 max in trained individuals. Training at or near lactate threshold improves the body's ability to clear lactate and sustain higher intensities for longer periods. It approximately corresponds to the upper boundary of Zone 3 or lower boundary of Zone 4 in heart rate-based training.