Background and aims: Ectopic lipid storage is implicated in type 2 diabetes pathogenesis; hence, exercise to deplete stores (i.e., at the intensity that allows for maximal rate of lipid oxidation; MLO) might be optimal for restoring metabolic health. This intensity (“Fat_max”) is estimated during incremental exercise (“Fat_max test”). However, in “the field” general recommendations exist regarding a range of percentages of maximal heart rate (HR) to elicit MLO. The degree to which this range is aligned with measured Fat_max has not been investigated. We compared measured HR at Fat_max, with maximal HR percentages within the typically recommended range in a sample of 26 individuals (Female: n = 11, European ancestry: n = 17). Methods and results: Subjects completed a modified Fat_max test with a 5-min warmup, followed by incremental stages starting at 15 W with work rate increased by 15 W every 5 min until termination criteria were reached. Pulmonary gas exchange was recorded and average values for V˙ o₂ and V˙ co₂ for the final minute of each stage were used to estimate substrate-oxidation rates. We modeled lipid-oxidation kinetics using a sinusoidal model and expressed MLO relative to peak V˙ o₂ and HR. Bland-Altman analysis demonstrated lack of concordance between HR at Fat_max and at 50%, 70%, and 80% of age-predicted maximum with a mean difference of 23 b·min⁻¹. Conclusion: Our results indicate that estimated “fat-burning” heart rate zones are inappropriate for prescribing exercise to elicit MLO and we recommend direct individual exercise lipid oxidation measurements to elicit these values.