This study developed a 3² factorial framework for optimising 500 mg metformin hydrochloride sustained-release matrix tablets using guar gum and hydroxypropyl methylcellulose K100M (HPMC K100M). Guar gum and HPMC were varied independently at 10, 15 and 20% w/w. Nine batches were assessed for granule flow, tablet hardness, friability, assay and drug release over 12 hours. Drug release at 1, 4, 8 and 12 hours served as optimisation responses. Increasing either polymer progressively reduced release, while high combined concentrations caused incomplete terminal release. ANOVA showed significant models for all four responses, with adjusted R² values from 0.942 to 0.978. HPMC produced the larger negative coefficient, although the interaction between polymers became more evident at later time points. Numerical desirability optimisation identified 16% guar gum and 17% HPMC K100M. The confirmation batch released 25.1, 50.4, 76.3 and 95.2% at 1, 4, 8 and 12 hours, respectively, with prediction errors below 2%. The work illustrates how factorial design can locate a balanced formulation region and avoid the limitations of one-factor-at-a-time development. Experimental confirmation remains essential.