Two novel univariate calibration methods, namely the extended ratio subtraction method (EXRSM) and the simultaneous ratio subtraction method (SRSM) were employed for the simultaneous determination of catechol (CT) and hydroquinone (HQ) in synthetic binary mixtures. The precision, accuracy, and specificity of these methods were statistically compared to those obtained from the derivative method (as a univariate calibration method), and the principal component regression (PCR) and the partial least squares (PLS) methods (as two multivariate calibration methods). Comparison of the results showed that there was no significant difference between the proposed methods. The main advantages of the proposed methods are that, unlike the other analytical methods, it is not necessary to use expensive apparatus and chemicals, and that they can be easily performed using a simple spectrophotometer that is available in all quality control labs. The developed methods were successfully applied for the simultaneous determination of CT and HQ with different ratios in tap water as the real sample.