Taxpayers whose income is not themselves within withholding, are expected to pay advance tax in three or four installments across the fiscal year. The annual return then works like a settlement where each installment is a credit against the final liability, and the department reconciles the two with interest charged on any shortfall. The mathematics is therefore decided by what you actually paid. Receipts or portal payment records for every installment must be preserved because the system matches your declared payments against departmental records, and a payment you cannot substantiate is a deduction you cannot prove. Underpayment is punished by interest on the difference from the date each installment fell due. The forward-looking habit is to re-estimate at every installment. If income jumps mid-year, a larger third installment avoids a painful settlement in return season, while genuinely falling income can justify a lower payment and a refund later. Speed matters in both directions, because the department refunds genuine overpayment only after your return is filed and verified.