Deductions only on actual payment restrict timing for employer contributions, taxes and interest, subject to limited return-date exceptions. Section 43B limits deductibility to the previous year in which specified sums are actually paid, covering taxes, employer welfare fund contributions, interest on loans from designated financial institutions and banks, leave encashment, railway asset payments, and delayed payments to micro or small enterprises. A proviso allows deduction if payment is made on or before the return-filing due date (except for micro or small enterprise delay). Explanations state prior-year allowance precludes later deduction, ''any sum payable'' may include liabilities not presently payable, and interest converted into instruments deferring liability is not deemed paid.