This paper presents a computational approach to accurately calculate the effects of the wafer-to-wafer oxide thickness (Tox) variations on the extracted TDDB parameters. Methodology relies on the available experimental data from the TDDB tests performed on wafers from the 0.35 ?? technology on the line of production. Wafer-level Tox variations are included too. Results show that the effects on gate-oxide lifetime are significant, ??-parameter variations are considerable, and ??-parameter variations are negligible.