If your contract or invoice states an interest rate for late payment, claim that rate from the due date. If it does not, courts and arbitrators award a reasonable rate (often 9% to 18% a year, simple) from the due date or the date of notice. MSME suppliers instead claim 3× the bank rate compounded; use the MSME calculator.
Making interest claimable
State the rate in your quotation, purchase order acceptance and invoice (“interest at 18% per annum on amounts unpaid after the due date”). A buyer who accepts the goods and the invoice without objection is generally bound by its terms. Mention the interest in every reminder and in the legal notice, computed to date.
Recovering the interest
Interest is claimed with the principal in the notice, the summary suit or the arbitration. FundRaksha’s advocates compute and claim it as standard; the free consultation tells you what is realistic for your documents. 30% only on recovery.