Formula, in Cardio Conditioning

Heart Rate Zone Formula (Karvonen)

Karvonen's reserve formula uses resting heart rate as a personalization anchor, which is more accurate than the basic %HRmax. Zone 2 — 60–70% of heart-rate reserve — is the aerobic-base workhorse.

4 variables. Published Mar 12, 2026. Updated May 10, 2026. By AI Fit Hub.

Education, not medical advice. The result comes only from the published formula and your inputs. How we check our formulas.

Formula

target_HR = (HRmax − HRrest) × intensity_pct + HRrest
HRmax (Tanaka 2001) = 208 − 0.7·age

Variables

target_HR

Target heart rate

Beats per minute. The middle of a training zone for the intensity prescribed.

HRmax

Maximum heart rate

BPM. Tanaka 2001 formula: 208 − 0.7·age. More accurate than the legacy 220 − age, especially for over-40s.

HRrest

Resting heart rate

BPM, measured first thing in the morning before getting up, after at least 5 minutes lying still. Average 3–5 days.

intensity_pct

Intensity percentage

Decimal. Zone 1 (recovery): 0.50–0.60; Zone 2 (aerobic base): 0.60–0.70; Zone 3 (tempo): 0.70–0.80; Zone 4 (threshold): 0.80–0.90; Zone 5 (VO₂max): 0.90–1.00.

Step by step

1

Estimate HRmax. Tanaka 2001 (208 − 0.7·age) is the strongest population estimate. A measured max test is more accurate when available.

Age 30: HRmax = 208 − 0.7·30 = 187 BPM.
2

Measure resting heart rate over several mornings.

5-day morning average: 58 BPM.
3

Compute heart rate reserve: HRmax − HRrest.

187 − 58 = 129 BPM reserve.
4

Apply the intensity percentage and add HRrest back. For Zone 2 use 0.60 to 0.70.

60% Z2 floor: 129 × 0.60 + 58 = 135 BPM. 70% Z2 ceiling: 129 × 0.70 + 58 = 148 BPM. Zone 2 = 135–148 BPM.

Worked example

30-year-old, HRrest 58, Zone 2 target

Age

Resting HR

Zone

Zone 2 (60–70% HRR)

HRmax = 187. HRR = 129. Z2 floor = 0.60·129 + 58 = 135. Z2 ceiling = 0.70·129 + 58 = 148.

Zone 2: 135–148 BPM. Aerobic base work — should be able to hold a conversation. Most easy runs and the bulk of marathon training live here.

Common variations

%HRmax: target_HR = HRmax × intensity_pct. Simpler but ignores cardiac fitness reflected in HRrest.

Lactate threshold-based: 'aerobic threshold' (LT1) corresponds to ~70–75% HRmax; 'anaerobic threshold' (LT2) to ~85–90% HRmax. Lab testing required.

Talk test: if you can hold a full conversation, you're in Zone 2. Broken sentences = Zone 3. Single words = Zone 4+.

Run the numbers next

Cardio Zone 2 Heart Rate Calculator
Calculate your Zone 2 heart rate with Maffetone, Karvonen, % Max HR, and lactate threshold methods compared side by side.
Cardio VO2 Max Estimator
Estimate aerobic capacity with the Cooper 12-minute run or Rockport 1-mile walk field tests.
Cardio Cycling Power & FTP Zone Calculator
Calculate your 7 Coggan power training zones from FTP or a 20-minute test result with W/kg ratio.

Sources

Tanaka H et al. Age-predicted maximal heart rate revisited , Journal of the American College of Cardiology (2001)
Karvonen MJ, Kentala E, Mustala O. The effects of training on heart rate; a longitudinal study , Annales Medicinae Experimentalis et Biologiae Fenniae (1957)