Background/purpose: This study aimed to investigate the differences among the equations used in estimating the reliability coefficient using the half-split method. These equations demonstrate Spearman-Brown's, Rulon's, Guttman's, Mosier's, Flanagan's, and Horst's. Materials/methods: The study instrument was a 43-item scale for evaluating the computerized mathematics curriculum for the tenth grade in southern Jordan. It was applied to a sample of 303 male and female teachers and educational supervisors. Results: The results showed that all values of the reliability coefficients estimated in the six equations were acceptable. In addition, the best equation for estimating the half-split reliability coefficient was the Spearman-Brown equation, followed by two equations by Flanagan and Rulon. Conclusion: Considering the results of the current study, the researchers do not recommend using Mosier's equation because it gave the lowest reliability-coefficient value.