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GST Compliance Utility

GST Interest Calculator

Calculate estimated interest for delayed GST return payments and separately calculate interest on wrongly availed and utilised ITC for notice and reversal scenarios.

Last updated: 16 August 2026
GSTR Interest

GST Return Interest Calculator

Estimated interest on delayed payment of GST liability in a return. Default rate: 18% per annum.

Interest period starts from the day after the applicable due date.
Default calculation rate used by this tool.
Optional. Minimum Electronic Cash Ledger balance available during the delay period.

Tax Liability

For an estimate of net cash liability. Does not model every credit-utilisation sequence.
How the estimate works: Interest is calculated using the 18% annual rate and a 365-day year. For delayed GSTR-3B interest, the GST portal's January 2026 enhancement provides for the minimum Electronic Cash Ledger balance during the delay period; this tool includes an optional ECL field for an estimate.
ITC Reversal

ITC Notice / Reversal Interest Calculator

Estimate interest where wrongly availed or excess ITC has been utilised and is being reversed or paid back.

Interest is calculated up to this date.
This tool uses 18% as the default practice setting.
Important: Enter the date on which the relevant ITC was completely utilised according to the facts and ledger position of the case. The date should not be selected merely because the credit was availed.
IGST ITC
CGST ITC
SGST / UTGST ITC
Legal/practice note: This calculator uses 18% as the default practice setting. The actual statutory rate applicable to wrongly availed and utilised ITC should be verified for the relevant period and legal provision.
Interest = ITC Amount × 18% × Number of Days ÷ 365

Understanding GST Interest

GST Return Interest

Interest may arise where tax remains unpaid beyond the applicable due date. For the return-interest calculator, OKOSUM uses an 18% annual rate and the actual number of delayed days entered by the user.

Interest on Wrongly Availed and Utilised ITC

ITC interest is a separate calculation from ordinary delayed return interest. Where wrongly availed ITC has been utilised, the applicable utilisation date and reversal/payment date are important to the interest period.

Why are IGST, CGST and SGST shown separately?

Separate head-wise fields make it possible to capture different utilisation dates and calculate an individual interest amount for each head rather than assuming one common date.

What does "completely utilised" mean?

For a wrongly availed ITC calculation, the relevant utilisation date is tied to utilisation of the wrongly availed credit and the Electronic Credit Ledger position. Users should use the date supported by their ledger and case records.

Can the GST portal's interest amount differ from this calculator?

Yes. This is an independent estimate. The GST portal can apply system validations, ledger data and return-specific rules. For GSTR-3B, the GST portal introduced an enhanced interest calculation from the January 2026 tax period.

Disclaimer: OKOSUM is an independent GST utility platform and is not affiliated with or endorsed by the Government of India, GSTN or any government department. Results are estimates for informational purposes and should not be treated as an official demand, notice computation or legal/tax opinion. Verify the applicable law, notifications, circulars, portal computation and case-specific facts, and consult a qualified GST professional for complex matters.

Legal reference points used in this tool include Section 50 of the CGST Act, Rule 88B of the CGST Rules and the GSTN advisory on the enhanced GSTR-3B interest calculation from the January 2026 tax period.

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