The objectives were to develop equations for predicting ileal digestible phosphorus (P) based on nonphytate P, phytate P, calcium to nonphytate P ratio, and exogenous phytase concentrations in broiler diets and to evaluate the accuracy of the models. The modified Michaelis–Menten model was used to predict apparent ileal digestible (AID) or standardized ileal digestible P in broiler diets. Two different methods were used to analyze 25 published ileal digestible P data to evaluate the accuracy of the equation for predicting AID P. The first method assessed mean and linear biases. While the mean bias was significant (P < 0.05), the linear bias was not significant. The second method involved regressing the 25 AID P data against those predicted by the current model. The results showed that the intercept and slope of the regression were not statistically different from 0 and 1, respectively. This suggests that the current equation accurately represents the test data. In conclusion, the accuracy of the model depends on validation processes. Considering that the current model was developed using various phytase products, it would be preferable to use an equation that is based on a single phytase product if requisite quantity of data is available.