Key Takeaways
- From the January 2026 tax period onwards, interest in Table 5.1 of GSTR-3B is auto-populated by the GST portal based on the revised Rule 88B formula and is no longer freely editable.
- Interest is charged only on the net shortfall in your Electronic Cash Ledger (ECL) between the due date and the date you actually offset the liability, not on gross tax liability.
- The system-computed figure is the minimum interest payable. Taxpayers can revise it upward but cannot reduce it below the portal value.
- The rate is 18 percent per annum under Section 50(1) of the CGST Act, 2017 for delayed tax payments.
- If you filed a late GSTR-3B for the January 2026 period, the auto-calculated interest shows up in the February 2026 GSTR-3B in Table 5.1.
Many Indian businesses filing their March 2026 GSTR-3B after the delayed portal availability are now opening Form GSTR-3B and seeing a pre-filled interest figure in Table 5.1 that they did not enter manually. This is the practical impact of GSTN Advisory dated 30 January 2026 and the follow-up advisories issued through February 2026. This guide explains exactly what changed, how the new interest formula works, and what to do when the auto-populated figure does not match your own working.
What Changed in January 2026?
Until December 2025, taxpayers who paid GST after the due date calculated interest themselves and entered it manually in Table 5.1 of GSTR-3B. The GST portal did not validate the figure. Many businesses under-reported interest by computing it on the wrong base (for example, on the net liability after Input Tax Credit rather than the cash shortfall) and faced scrutiny notices later.
From the January 2026 tax period onwards, the GST Network auto-populates Table 5.1 using a revised computational logic that directly applies the proviso to Rule 88B(1) of the CGST Rules, 2017. The portal now gives the taxpayer the benefit of the minimum cash balance that was already sitting in the Electronic Cash Ledger (ECL) from the due date till the date of offset, and charges interest only on the net shortfall.
The first live impact was visible in the February 2026 GSTR-3B filing, which carried auto-populated interest for any late payment relating to the January 2026 period.
The Revised Interest Formula
The interest computation now follows this logic:
Interest = (Net Tax Liability in cash for the period minus Minimum cash balance available in the ECL from the due date to the date of debit) × (Number of days of delay / 365) × 18%
Three things to notice:
- Cash portion only. The base is the part of your liability you were supposed to pay in cash, after ITC was applied. Interest does not apply on the ITC-offset portion.
- Minimum ECL balance gives relief. If you already had money sitting in the ECL on the due date, the portal treats that as partial discharge. You pay interest only on the gap.
- 18 percent per annum under Section 50(1). The rate is unchanged. Only the base and the way it is calculated have changed.
Worked Example
A Hyderabad trading company has a cash liability of Rs 4,00,000 for the January 2026 GSTR-3B. The due date is 20 February 2026. The return is actually filed on 10 March 2026 (18 days late). The Electronic Cash Ledger had Rs 1,50,000 continuously available from 20 February to 10 March.
Under the new formula:
- Net shortfall = Rs 4,00,000 minus Rs 1,50,000 = Rs 2,50,000
- Interest = Rs 2,50,000 × 18 / 100 × 18 / 365 = Rs 2,219
Under the old approach many tools would have charged interest on the full Rs 4,00,000, producing Rs 3,551. The new portal logic reduces it to Rs 2,219 because the ECL balance was lying idle the entire time.
Table 5.1 is Now "Editable Upward Only"
This is the behaviour that most taxpayers miss on their first post-January filing.
- The portal-computed figure is the minimum interest payable for that period.
- You can increase the figure if you have a reason to pay more (for example, to settle a notice or to match an officer's working).
- You cannot reduce the figure below what the system has computed, even if your internal working produces a lower number.
If you believe the portal figure is wrong because the ECL history has been misread, the correction route is to raise it through the GST helpdesk or during the reconciliation in your GSTR-9 annual return, not by overriding Table 5.1 during filing.
Why Many Businesses See "Unexpected" Interest in Their GSTR-3B
Three situations cause the pre-filled number to differ from what finance teams expect:
1. Interest from an earlier period appears in a later return. Interest on delayed payment of the January 2026 tax period shows up in the February 2026 GSTR-3B, because that is the first return filed after the delayed payment. Teams that look only at the current period's liability and ignore the Table 5.1 carry-forward get surprised.
2. Finance team calculated on gross liability. Older ERP systems still compute interest on the full output tax before ITC offset. The portal now charges it only on the post-ITC cash shortfall. Your internal figure will be higher than the portal figure in most cases.
3. ECL was debited and re-credited during the delay window. The portal looks at the minimum cash balance across the whole delay period. If you paid out of the ECL on day 3 and re-funded on day 10, the minimum balance between due date and offset may be zero, and interest will be charged on the full shortfall.
What You Should Do Before Filing the Next GSTR-3B
- Open Table 5.1 before you hit Submit. Do not rely on your offline working. The portal figure is now binding as a floor.
- Reconcile the ECL movement. Download the Electronic Cash Ledger statement for the period from the due date through the payment date. The minimum balance during that window is what the portal used.
- Keep a working paper. Save a screenshot of Table 5.1 and the ECL statement together. If a notice comes later, this is your evidence of how the interest was determined.
- Do not try to override downward. Pay the system figure. Dispute it through the grievance route or at annual return stage if you genuinely disagree.
- Review your cash management policy. Because the portal now rewards minimum ECL balance during a delay, depositing cash into the ECL before the due date can meaningfully reduce interest if you anticipate a late filing.
How This Connects to Recent GST Enforcement Changes
The auto-interest mechanism is part of a broader January-to-April 2026 shift toward system-driven enforcement. Taxpayers are already seeing:
- GSTR-3B blocked on ITC mismatch under the zero-mismatch policy
- Three-year filing cutoff barring returns beyond the window
- GST 2.0 Aadhaar and intermediary rules effective April 2026
The direction is consistent: manual discretion is being squeezed out of the return and replaced by portal-driven computation. Finance teams that keep their ECL and filing calendar clean will see the smallest interest bills. Teams that ignore reconciliation will find that the portal has already decided the number before they open the return.
Let Tax Garden Handle the Interest Reconciliation
Reading Table 5.1 correctly, matching it to the ECL movement, and keeping the supporting papers is slow work to do alone every month. Tax Garden runs the reconciliation for you, flags the exact reason for any auto-populated interest, and files GSTR-3B so late filings happen only when they have to. See our GST compliance plans or talk to our team.
