Personal income tax represents a fundamental component of modern fiscal systems, contributing to government revenue mobilisation, redistribution of income, and promotion of social equity. Despite its importance, the structure and effectiveness of personal income taxation vary significantly across countries due to differences in economic development, institutional capacity, and policy priorities. This study undertakes a comparative analysis of personal income tax systems in India, the United Kingdom, and the United States, with specific reference to individual taxpayers. Using secondary quantitative data drawn from official national sources and international databases over a multi-year period, the study examines statutory tax structures, exemption thresholds, progressivity, and revenue performance. Descriptive and comparative analytical methods are employed, supported by graphical analysis and selected statistical indicators. The findings reveal that higher personal income tax revenue is associated more strongly with broader tax bases, effective withholding mechanisms, and administrative efficiency than with higher statutory tax rates alone. The study concludes by deriving policy-relevant insights for strengthening personal income taxation in developing economies, particularly India.