This document presents a proposed closed-form expression for estimating the minimum operating voltage (vddmin) of CMOS D flip-flops, which is critical for ensuring functional error-free operation in circuits. It demonstrates that vddmin is a linear function related to the square root of the logarithm of the number of flip-flops and is influenced by manufacturing variations. The findings validate the dependence of vddmin on logic gate count and provide insights into optimizing circuit design for energy efficiency.