This blog post provides a comprehensive overview of Section 201(1A) of the Income Tax Act, 1961, focusing on the interest levied for delayed TDS deduction or payment. It explains the two distinct scenarios for interest calculation (1% for failure to deduct, 1.5% for failure to pay after deduction), clarifies the "month or part of a month" rule, and illustrates calculations with clear examples. Furthermore, it details the severe implications for defaulting deductors, including "assessee in default" status, disallowance of expenditure under Section 40(a)(ia), various penalties (271C, 271H), and potential prosecution. The post concludes with practical best practices to help deductors ensure timely compliance and avoid these costly repercussions.