Repeatability is a key statistic in quantitative genetics, measuring the proportion of variance in a trait that is due to individual differences rather than within-individual variation. However, many papers have incorrectly calculated repeatability. This article outlines the correct method for calculating repeatability, highlights a common mistake, and provides a method for checking published values and estimating repeatability from F ratios. Repeatability (r) is calculated as r = s_A² / (s² + s_A²), where s_A² is the among-group variance component and s² is the within-group variance component. These components are derived from an ANOVA. The correct calculation involves using the mean squares from the ANOVA and adjusting for group size. A common mistake is equating Falconer's "variance" with mean square, leading to the incorrect calculation of MS_A/(MS_w + MS_A) instead of repeatability. This value is always greater than the true repeatability, especially when group sizes are unequal. An approximate value of repeatability (r_approx) can be calculated from the F ratio and degrees of freedom using r_approx = (F - 1)/(F - 1 + n̄), where n̄ is the average group size. This method provides a conservative estimate and is useful for checking published values. Examples show that using this method can reveal miscalculations in published studies. The authors recommend that authors, referees, editors, and readers ensure that repeatability is calculated correctly and that published values are accompanied by associated F ratios.Repeatability is a key statistic in quantitative genetics, measuring the proportion of variance in a trait that is due to individual differences rather than within-individual variation. However, many papers have incorrectly calculated repeatability. This article outlines the correct method for calculating repeatability, highlights a common mistake, and provides a method for checking published values and estimating repeatability from F ratios. Repeatability (r) is calculated as r = s_A² / (s² + s_A²), where s_A² is the among-group variance component and s² is the within-group variance component. These components are derived from an ANOVA. The correct calculation involves using the mean squares from the ANOVA and adjusting for group size. A common mistake is equating Falconer's "variance" with mean square, leading to the incorrect calculation of MS_A/(MS_w + MS_A) instead of repeatability. This value is always greater than the true repeatability, especially when group sizes are unequal. An approximate value of repeatability (r_approx) can be calculated from the F ratio and degrees of freedom using r_approx = (F - 1)/(F - 1 + n̄), where n̄ is the average group size. This method provides a conservative estimate and is useful for checking published values. Examples show that using this method can reveal miscalculations in published studies. The authors recommend that authors, referees, editors, and readers ensure that repeatability is calculated correctly and that published values are accompanied by associated F ratios.