GST compliance is a calendar problem before it is an accounting problem. GSTR-1 on the 11th, GSTR-3B on the 20th (or the 22nd/24th under QRMP), IFF on the 13th, CMP-08 quarterly, GSTR-4 by 30 June, GSTR-9 by 31 December — and each missed date costs ₹50 a day plus 18% interest on tax. This calendar builds the full FY 2026-27 schedule for your filing profile — monthly, QRMP or composition — shows the next deadline at a glance, and exports every date as an .ics file for Google or Outlook Calendar.
The return cycle in one table
| Return | Who | Frequency | Due date |
|---|---|---|---|
| GSTR-1 | Regular taxpayers (monthly) | Monthly | 11th of the next month |
| IFF | QRMP taxpayers wanting to pass ITC monthly | Optional, months 1–2 of a quarter | 13th of the next month |
| GSTR-1 (quarterly) | QRMP taxpayers | Quarterly | 13th of the month after the quarter |
| GSTR-3B | Regular (monthly) | Monthly | 20th of the next month |
| GSTR-3B (QRMP) | Turnover up to ₹5 crore, opted in | Quarterly, with PMT-06 monthly by the 25th | 22nd (southern/western states) or 24th (others) of the month after the quarter |
| CMP-08 | Composition dealers | Quarterly | 18th of the month after the quarter |
| GSTR-4 | Composition dealers | Annual | 30 June following the financial year |
| GSTR-9 / 9C | Turnover above ₹2 crore / ₹5 crore | Annual | 31 December following the financial year |
The calendar applies the state rule for the QRMP 3B date automatically. A narrative walk-through of the year, including the IMS steps between GSTR-1 and 3B, is in GST due dates FY 2026-27.
Two rules that changed the stakes
Hard-locking of GSTR-3B: the tax liability in 3B is now auto-populated from GSTR-1/IFF and cannot be edited downward; corrections go through GSTR-1A before filing 3B. The three-year bar: returns cannot be filed more than three years after their due date, which permanently blocks late filing (and the ITC in it). Both are explained in GSTR-3B hard-locking and the 3-year filing bar. Since GSTR-2B is generated from what suppliers file and what you accept in IMS, your own GSTR-1 timing affects your customers' credit too; see GST IMS explained.
How to use the calendar
- Choose your profile: monthly, QRMP (and your state), or composition.
- Pick the financial year; FY 2026-27 loads by default.
- Scan the month-wise cards; the next due date is highlighted with the days remaining.
- Download the
.icsfile and import it into Google Calendar or Outlook — every date becomes an all-day event with a reminder. - Re-download if you switch schemes mid-year; QRMP opt-in/opt-out happens quarterly.
Late fees and interest
- Late fee: ₹50 per day (₹25 CGST + ₹25 SGST), or ₹20 per day for nil returns, capped by turnover — ₹500 for nil, ₹2,000 for turnover up to ₹1.5 crore, ₹5,000 up to ₹5 crore, ₹10,000 above, per return.
- Interest: 18% per annum on tax paid late, computed on the net cash liability from the due date to the payment date.
- GSTR-1 not filed blocks GSTR-3B filing; two consecutive 3Bs unfiled can block e-way bill generation.
- Compute the interest for a late payment with the late payment interest calculator in simple-interest mode.
Practical rhythm for a small business
- By the 5th: close the previous month's sales register from your GST invoices; reconcile purchase invoices with GSTR-2B.
- By the 10th: file GSTR-1 (or IFF) so your B2B customers see ITC on time.
- By the 18th: check IMS actions, compute cash liability, arrange funds.
- By the 20th: file 3B and pay. Use the business days calculator if a due date lands on a Sunday — extensions are not automatic.
Related tools
- GST invoice generator — the source of your GSTR-1 data.
- GST calculator — check liability figures.
- Late payment interest — 18% interest on delayed tax.
- Business days calculator — count working days to a deadline.
- EDF filing helper — the FEMA deadline that now sits alongside your GST dates.
- HSN/SAC finder — HSN summary in GSTR-1 needs correct codes.