GST Interest Calculation Changes 2026: Revised Rules & GSTR-3B Tax Liability Breakup

Understand the new GST interest calculations rules along with revised interest calculation formula for delayed filings of GSTR 3B implemented in 2026 

The 30th January 2026 GSTN advisory has enhanced the interest calculations on delayed filings and payments of GSTR 3B from the January 2026 tax period. The interest will be computed automatically by the portal and will be reflected in Table 5.1 of GSTR 3B. 

Key Takeaways

• The interest calculation procedure has been automated by the GST portal with applying a revised interest calculation formula.
• This enhancement facilitates the benefit of minimum cash available in the Electronic cash ledger of the taxpayer from the due date of payment of tax.
• The revised interest calculation formula is Interest = (Net Tax Liability – Minimum Cash Balance in ECL from due date to date of debit) × (No. of days delayed / 365) × Applicable Interest Rate
• The interest is calculated only on the net shortfall in the Electronic Cash Ledger (ECL) after the due date of payment and not on the entire tax liability.

Background of GST Interest Levy

The revised computation formula considers only the minimum cash available in the Electronic Credit Ledger (ECL) of the taxpayer from the due date of payment of tax.

• To begin with, Section 50 of the CGST Act, 2017 states that a taxpayer is liable to pay interest for the delay made in filing GSTR 3B and making the payment of tax. Hence, interest at 18% is mandatorily payable on delayed tax payments, and this section specifies when interest is payable on tax.
• Rule 88B of the CGST Rules, 2017 states how the interest on such delayed tax payment is to be calculated, i.e., interest is payable only on the portion of the tax paid through ECL of the taxpayer, and no interest is payable on the tax paid by utilising ITC.
• Further, the proviso to Rule 88B states that no interest will be payable on the portion of the tax paid through ECL if the cash was deposited on or before the due date, even if the return for the period is filed after the due date.

Key Features of the Revised GST Interest Calculation

Here are the Key Features of the GSTN’s Advisory dated 30th January 2026:

1. System-Computed Interest – 

The amount of interest is auto-populated by the portal on the basis of the revised computational formula in Table 5.1 of GSTR 3B. This is the minimum interest to be payable by the taxpayer and thus cannot be edited by the taxpayer to downvalue the auto-computed interest.

2. Auto population of tax liability breakup in GSTR 3B –

For the filing of GSTR-3B from the January 2026 tax period onwards, the GST Portal shall auto-populate the “Tax Liability Breakup Table” in GSTR-3B on the basis of the date of
documents related to supplies reported in GSTR-1 / GSTR-1A / IFF pertaining to any previous tax period. Where the corresponding tax liability has been discharged in the current period’s GSTR-3B.

Auto-populated values are suggestive in nature. Taxpayers may increase these values based on their own records and computations, if required.

The auto-populated breakup can be viewed at:
Login → GSTR-3B Dashboard → Table 5.1 (Payment of Tax) → Tax Liability Breakup

3. Update in Table 5.1 – Suggestive Cross-Utilisation of ITC – 

From January-2026 period onwards, once the available IGST ITC has been fully exhausted, the GST Portal will allow paying IGST liability in Table 6.1 of GSTR-3B using available CGST and SGST ITC in any sequence.

4. Collection of Interest in GSTR-10 for Delayed Filing of Last Applicable GSTR-3B –

In case of cancelled taxpayers, if the last applicable GSTR-3B return has been filed after the due date, then the interest applicable on such delayed filing shall be levied and collected through the Final Return, i.e., GSTR-10. 

Apart from the Table 5.1 of GSTR-3B, the interest due from last period payable in current month's GSTR-3B shall be auto-populated in the tab ‘Tax Liability Breakup, As Applicable’ from February 2026 return onwards, as per the GSTN advisory dated 16th March 2026.

GST Revised Interest Calculation Formula

Interest = (Net Tax Liability – Minimum Cash Balance in ECL from due date to date of debit)
× (No. of days delayed / 365) × Applicable Interest Rate

The most significant feature of the revised computation formula is the use of the minimum available cash balance (lowest daily balance) in the Electronic Cash Ledger between the due date and the payment date.

Let us Understand the Formula with a Simple Example:

The GST payable in cash is Rs.1,00,000. The due date to pay such tax is on 20^th Feb 2026, but the payment is made on 5^th March 2026, i.e., 13 days' delay. 

Let us assume that the cash available in ECL is Rs.40,000 deposited before 20^th Feb, and the remaining Rs.60,000 is deposited on 5^th March. Interest payable at 18%.

Solution: The interest is payable only on the amount of shortfall existed on the due date, i.e.,

Net Tax Liability Rs.1,00,000 – Minimum Cash Balance in ECL from due date Rs.40,000 = Rs.60,000.

Thus, interest is payable on Rs.60,000

= 60,000 X 18% X 13/365 days

= Rs.384.

• Rs.384 will be auto-populated in Table 5.1 of GSTR-3B.
• This represents the minimum interest payable as per the revised system.
• Interest is not charged on the entire Rs.1,00,000.