GST monthly checklist for FY 2026-27

Every recurring filing your firm owes for a regular monthly GST taxpayer in FY 2026-27. Print, pin to the cubicle wall, work through it on the 4th of every month.

For each registered client, every month

1. By 5th — Reconcile sales register against GSTR-2A/2B for the previous month. Flag missing invoices from suppliers; chase them.
2. By 8th — Issue + collect any debit/credit notes for the prior month. Update HSN/SAC if any product mix shifted.
3. By 11th — File GSTR-1 (outward supplies). Late fee ₹50/day, cap ₹5,000 per form. Once filed, the ARN is the proof — save it under documents → year → month for that client.
4. By 13th — If client is on QRMP, file IFF for invoice furnishing.
5. By 14th — Pull GSTR-2B (auto-populated). Reconcile ITC vs books. Flag any ineligible ITC under Sec 17(5).
6. By 17th — Compute net tax liability for GSTR-3B. Generate challan if cash payment needed. Send to client for funds.
7. By 20th — File GSTR-3B with DSC/EVC. Interest at 1.5% per month if liability not paid. Save ARN.
8. By 25th— If applicable, file ITC-04 (job-work) for the half-year if your client's turnover is ≤5 cr (above 5 cr, this is quarterly).

Quarterly events to layer on top

• Q1, Q2, Q3, Q4 end + 18 days — CMP-08 if any client is on composition scheme.
• FY end + 9 months — GSTR-9 (annual return) if turnover ≥ ₹2 cr.
• FY end + 9 months — GSTR-9C (reconciliation, CA-attested) if turnover ≥ ₹5 cr.

The 5 mistakes that consistently cost late fees

1. Filing GSTR-1 in the wrong tax period (B2B invoice dated end-of-month, filed in next month).
2. Forgetting to file when there's zero turnover. Late fee accrues on nil returns too.
3. Not reversing ITC on supplier non-filing — comes back later as a notice with interest.
4. Mixing intra-state and inter-state on the same invoice (most software prevents this; spot-check anyway).
5. Place of supply incorrectly defaulted to the firm's state — should be the client's.