Monthly GST taxpayers face the September GSTR-3B deadline on October 20, 2026. Quarterly Return Monthly Payment filers follow on October 22 or October 24, depending on state grouping. For students, interns, and young finance teams, this weekend matters. Use a focused checklist to prevent DRC-01C blocks, interest costs, and portal slowdowns.
Begin with input tax credit hygiene. Match GSTR-2B with purchase books, tag ineligible credits, and compute reversals under Rule 42 and Rule 43. Tie up reverse charge entries. Then compare GSTR-1 and GSTR-3B to close outward tax gaps. Resolve any DRC-01C prompt early. Plan cash versus credit to avoid avoidable interest.
GSTR-3B due dates: who files by 20, 22 and 24 October
File September GSTR-3B by October 20 if you are a monthly filer. QRMP taxpayers have staggered windows on October 22 and October 24. Check your state grouping on the portal before scheduling challans. Teams supporting multiple GSTINs should prioritise high liability entities first, then smaller units with simpler reconciliations.
ITC weekend fixes: 2B versus books, Rule 42/43 and RCM
Lock the eligible credit number before drafting 3B. Remove blocked credits, vendor-debit notes, and timing mismatches from the pool. Compute Rule 42 common credit reversal using exempt turnover ratios. Review capital goods reversal under Rule 43. For reverse charge liabilities, pay tax in cash and then record eligible credit accurately.
| Check | Quick formula | Action |
|---|---|---|
| ITC 2B versus books | Books eligible ITC − 2B eligible ITC | Trim ineligible; chase vendors for missing invoices. |
| GSTR-1 versus 3B | GSTR-1 taxable value − 3B taxable value | Pay shortfall; document reasons for variance. |
| Reverse charge (RCM) | RCM base × rate − tax already paid | Discharge in cash; claim eligible credit thereafter. |
| Rule 42/43 reversal | Common credit × exempt turnover ratio | Reverse now; track interest if delayed. |
DRC-01C alerts: clear mismatches before the portal blocks
DRC-01C flags variances between GSTR-1 and 3B or 2B and 3B. Do not ignore it over the weekend. Provide a reasoned response, attach workings, and pay differential tax if needed. Non-response can halt subsequent workflows, including furnishing GSTR-1, until the discrepancy is addressed on the portal.
Cash and credit planning: interest, late fee and bank limits
Compute interest on net cash liability at eighteen percent per annum. Use liability × 18 percent × days divided by 365. Wrongly availed and utilised credit typically attracts twenty-four percent. Late fees apply per day, with notified turnover-based caps. Prepare challans early, and respect bank, UPI, and net-banking transaction limits.
Portal tactics and proof: staggered filing windows, challans and ARN
Avoid peak hours near midnight on October 20, 22 and 24. Generate challans using NEFT or RTGS if bank limits pinch. Keep CPIN copies, payment receipts, and acknowledgement reference numbers. Save the filed return summary and liability ledger screenshots. These artefacts close review loops during audits, placements, or client appraisals.
After filing, reconcile e-invoice and e-way bill data with sales registers. Tag vendors whose invoices missed GSTR-2B and initiate quick follow-ups. Archive workings and variance notes for interviews, internal reviews, and client briefings. Meet the October 20, 22 or 24 cut-offs confidently, and turn this compliance sprint into a career-strengthening habit.
