Abstract We illustrate that the Organisation for Economic Co-operation and Development guideline 305 (OECD-305) for growth-correcting bioconcentration factors (BCFs) and biomagnification factors (BMFs) violates the mass-balance assumption underlying the definition of BCFs and BMFs and provides unrealistic estimates of BCFs and BMFs of chemicals in nongrowing fish. We present and test alternative methods for growth-correcting BCFs and BMFs that maintain mass balance. We conclude that the OECD-305-recommended growth correction of BCFs and BMFs causes error, is unnecessary, and should be revisited. Environ Toxicol Chem 2019;38:2065–2072. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC. Abstract Effect of growth on bioconcentration factors and biomagnification factors.