The GSTR-3B due date for September 2026 was usually the 20th of the following month, so 20 October 2026 for monthly filers. If you file quarterly under the QRMP scheme, the Q2 (July–September) GSTR-3B was usually due on the 22nd or 24th of October, depending on your state. If you have not filed yet, this guide explains what the delay costs and how to catch up.
Dates here are statutory defaults. Extensions by notification do happen, so always confirm on the GST portal or the CBIC website before relying on any date.
GSTR-3B due date for September 2026: who files when
TaxpayerReturnUsual due date Monthly filer (regular)GSTR-3B for September20 October 2026 QRMP filer, Category X statesGSTR-3B for July–September22 October 2026 QRMP filer, Category Y statesGSTR-3B for July–September24 October 2026Which category your state falls in is listed on the GST portal. If a due date fell on a Sunday or a public holiday, check whether the portal moved it to the next working day.
What if you missed the September 2026 due date?
Do not wait for the next month. The late fee runs per day until you file, so every extra day adds to it. File the September return first, then the October return due on 20 November 2026. You cannot file a later month's GSTR-3B on the portal while an earlier one is pending.
Late fee for GSTR-3B: how it is calculated
The late fee under section 47 is charged per day of delay, split equally between CGST and SGST (or applied under IGST). The usual structure is:
- Return with tax liability: ₹50 a day (₹25 CGST + ₹25 SGST).
- Nil return: ₹20 a day (₹10 + ₹10).
- Maximum cap: depends on your annual turnover, and is lower for nil returns.
Because the caps and the slabs have been revised by notification over time, check the current notification on the CBIC website for your turnover bracket before computing the exact amount. The fee is paid in cash and cannot be set off against your ITC balance.
Interest on late GST payment
Interest is separate from the late fee. Under section 50, interest is usually charged at 18% a year on the tax you paid late, counted from the day after the due date until the day you pay. For wrongly claimed and utilised ITC the rate is usually 24% a year. Interest generally applies on the net tax payable in cash, not on the portion already covered by your ITC balance, but confirm your specific case with a CA.
A simple worked example: suppose your net cash liability for September was ₹1,00,000 and you paid 10 days late. Interest at 18% a year is roughly ₹1,00,000 × 18% × 10 ÷ 365 ≈ ₹493. Add the per-day late fee, and you can see why filing sooner is cheaper even when the cash is tight.
Steps to file a delayed GSTR-3B
- Match sales. Compare outward supplies in your books with what you reported in GSTR-1. Our GSTR-1 vs GSTR-3B reconciliation checklist shows how.
- Check ITC against GSTR-2B. Claim only credit that appears in your auto-drafted statement and is allowed. See our guide to GSTR-2B reconciliation before GSTR-3B and the list of blocked credits under section 17(5).
- Work out interest. The portal calculates interest on the liability paid late. Review the figure it shows in Table 5.1 before you pay.
- Fund the cash ledger. Create a challan for tax, interest and late fee, and allow time for the payment to reflect.
- File and keep proof. Offset the liability, submit with your authorised signatory, and save the acknowledgement.
Mistakes that make a late filing worse
- Filing a nil return when there were sales, which later needs correction.
- Claiming ITC for invoices missing from GSTR-2B just to reduce cash outgo.
- Paying the tax but never filing the return. Payment alone does not stop the late fee.
- Forgetting the time limits that sit around this season, such as the ITC time limit on 30 November 2026.
Key takeaways
- Monthly filers' GSTR-3B for September 2026 was usually due on 20 October 2026; QRMP filers on the 22nd or 24th.
- Late fee runs per day and is paid in cash; interest is charged separately.
- File the earliest pending month first; later months are blocked until then.
- Always confirm dates, caps and extensions on the official portal or with your CA.
If you keep your accounts in Smart Books, its GST section has a GSTR-3B return view where you can sync the portal data, save a draft and file, and a liability and ITC comparison that flags where GSTR-3B liability is lower than GSTR-1 or ITC claimed is higher than GSTR-2B. That makes it easier to catch mismatches before you file; read more on the Smart Books page.
