Two independent meters on a late GSTR-3B/GSTR-1: the Section 47 late fee, capped by last year’s turnover, and Section 50 interest at 18% p.a. — charged only on the tax actually paid through the cash ledger, not the gross liability before ITC set-off.
A client with ₹10 lakh gross output tax but ₹8.5 lakh of eligible ITC only pays interest on the ₹1.5 lakh actually settled through the cash ledger — not the ₹10 lakh gross figure. This retrospective clarification to Section 50(1) (Finance Act 2019, made retrospective from 1 July 2017 by the Finance Act 2021) is the single most common overstatement in manually computed GST interest demands.
Section 47 late fee for a non-nil GSTR-3B or GSTR-1: ₹50 per day of delay (₹25 CGST + ₹25 SGST), capped by the prior financial year's aggregate turnover — ₹2,000 for turnover up to ₹1.5 crore, ₹5,000 for ₹1.5-5 crore, ₹10,000 above ₹5 crore. A NIL return attracts a lower ₹20/day (₹10+₹10), capped at ₹500.
Section 50 interest applies at 18% per annum, computed on the number of days from the due date to the actual payment date — but only on the portion of tax actually discharged through the electronic CASH ledger, not the gross output tax liability before setting off available input tax credit. This was clarified with retrospective effect from 1 July 2017 (Finance Act 2019, made retrospective by the Finance Act 2021 amendment to Section 50(1)) after years of litigation over gross-vs-net computation.
A separate, harsher 24% p.a. rate applies under Section 50(3) to specific situations — undue or excess claim of input tax credit, or excess reduction in output tax liability — which this calculator does not model; those cases need a fact-specific determination, not the standard late-payment rate.
GSTR-3B due 20 May 2026, filed 15 June 2026 (26 days late). Turnover ₹3.2 crore last year (non-nil). Gross output tax ₹10 lakh, ITC available ₹8.5 lakh, so ₹1.5 lakh settled via cash ledger.
