If your business is registered under the GST composition scheme, you touch the return system only a handful of times a year — and that is exactly why the next deadline slips past people. The CMP-08 due date for July-September 2026 is 18 October 2026. CMP-08 is not a return you file to report information after the fact; it is the statement through which you actually pay the tax you owe for the quarter. Miss it, or under-state it, and interest starts running on money you have already built into your selling prices.
What the CMP-08 due date for July-September 2026 actually covers
Rule 62 of the CGST Rules requires a person paying tax under the composition levy to “furnish a statement, every quarter…, containing the details of payment of self-assessed tax in FORM GST CMP-08, till the 18th day of the month succeeding such quarter.” The GST portal describes the form in the same terms: it is “used to declare the details or summary of self-assessed tax which is payable for a given quarter.”
Two words in that rule carry the whole obligation. Self-assessed means no one hands you the figure — you work out your own tax on the quarter’s turnover and put it in the form. And payment means CMP-08 doubles as the challan: filing it is how the tax leaves your account. So for the July, August and September quarter just ended, the statement and the payment are both due on 18 October 2026, which falls on a Sunday — plan to have it done by the working day before, and do not assume the date shifts unless the government notifies an extension.
Why it is a payment, not a paperwork return
The composition scheme is built for simplicity: a small business pays tax at a low flat rate on turnover, cannot claim input tax credit, and issues a bill of supply rather than a tax invoice. Because the compliance is so light — one short statement a quarter instead of monthly GSTR-1 and GSTR-3B — it is easy to treat CMP-08 as a box-ticking exercise. It is not. The number you enter is the tax you are paying, and if it is short, the shortfall carries interest from the due date under the general GST rules, quietly, with no monthly return arriving to remind you it exists. By the time the annual return is prepared months later, a small quarterly under-payment has been accruing interest the whole time.
The trap with the composition scheme is not complexity — it is infrequency. You file so rarely that the quarterly payment feels optional. It is not; it is the tax itself.
The four CMP-08 dates across the year
Because the rule fixes the due date at the 18th of the month after each quarter, the whole year’s payment calendar is predictable. Put these four dates in your compliance diary once and the scheme runs itself:
| Quarter | CMP-08 due date |
|---|---|
| April – June | 18 July |
| July – September | 18 October |
| October – December | 18 January |
| January – March | 18 April |
The one on your desk right now is the second row: the July–September quarter, due 18 October 2026.
CMP-08 is not GSTR-4 — you owe both
Composition taxpayers have two separate obligations that are often confused. CMP-08 is the quarterly statement-cum-challan for paying the self-assessed tax — four times a year, each due on the 18th of the month after the quarter. GSTR-4 is the annual return that consolidates the year, due once, by 30 April following the end of the financial year. Paying your CMP-08 challans on time through the year does not discharge the annual return, and filing GSTR-4 does not make up for a quarter’s payment you skipped. This quarter’s job is the CMP-08 payment on 18 October; the annual GSTR-4 is a separate deadline for next April.
What to check before you file this quarter
Three checks are worth running before 18 October. First, confirm the scheme still fits — the composition route is meant for smaller businesses (broadly, up to ₹1.5 crore of turnover for goods and ₹50 lakh for services), and if you have crossed the limit during the year your obligations change. Second, capture any tax payable under reverse charge on inward supplies: composition dealers still owe this, and it belongs in the quarter’s self-assessed figure, not just the tax on your own sales. Third, reconcile the quarter’s turnover to your books before you commit the number, because the figure you enter is the figure you pay — there is no monthly return that will surface an error later.
None of this is heavy work — but it is real money leaving on a fixed date, and the light compliance load is precisely what makes it easy to forget. If you would rather have the computation checked and the statement filed on time — and the annual GSTR-4 handled when it falls — that is the kind of routine an outsourced finance team takes off your desk entirely.