CMP-08 by the 18th: The Quarterly Deadline Keeping Composition Dealers Compliant

The dates that move money in India are rarely the ones that make headlines. While the market watches the Reserve Bank of India's next Monetary Policy Committee meeting on 5-7 October 2026 and tracks the primary-market pipeline, roughly the busiest deadline for India's smallest registered businesses arrives quietly on the 18th. Form GST CMP-08, the statement-cum-challan of self-assessed tax, is due on the 18th of the month succeeding each quarter. For the July to September 2026 quarter, that means 18 October 2026 is the date every composition dealer should ring on the calendar.

This is a compliance event, not a market event, but for the lakhs of composition taxpayers who run kirana stores, small manufacturing units and neighbourhood restaurants, it is the single recurring cash outflow that keeps their registration clean. Miss it and interest starts running at 18% per annum. This watchlist sets out the deadline, the arithmetic and the surrounding calendar so no composition dealer is caught short in October 2026.

Statutory Deadlines

The headline entry on the watchlist is Form GST CMP-08 for the July-September 2026 quarter, due 18 October 2026. The form is filed on the GST portal and doubles as both a declaration of self-assessed quarterly tax and the challan through which that tax is paid. It must be filed by taxpayers registered under the composition levy of Section 10 of the CGST Act, 2017 - both those who registered as composition taxable persons through Form GST REG-01 and existing taxpayers who opted for the composition levy through Form GST CMP-02.

Because CMP-08 recurs on a fixed cadence, a composition dealer can plan the whole year in advance. The 18th of the month after each quarter is the constant, and there are four such dates:

CMP-08 is distinct from the annual return. A composition taxpayer files CMP-08 four times a year and then reconciles the whole year in a single Form GSTR-4, which is due by 30 June following the close of the financial year. For FY 2025-26 the GSTR-4 deadline of 30 June 2026 has already passed; for FY 2026-27 the annual return will be due by 30 June 2027. The quarterly CMP-08 on 18 October 2026 is therefore the next live filing obligation in the composition cycle, not the annual one.

Composition dealers should not confuse their quarterly rhythm with the monthly regular-scheme calendar. Regular taxpayers file GSTR-1 by the 11th and GSTR-3B by the 20th of each month, and e-commerce operators file GSTR-8 by the 10th - obligations covered in our note on the GSTR-8 TCS deadline. Composition dealers are spared that monthly grind precisely because they pay a fixed percentage of turnover through CMP-08 instead. Understanding how self-assessment tax works is central here: the dealer computes and pays the liability without a departmental assessment, which is why accuracy on the 18th matters.

Market Events

The composition deadline sits inside a broader October 2026 calendar that every small business should read alongside its own filing. The most consequential entry is the RBI Monetary Policy Committee meeting scheduled for 5-7 October 2026. At its previous review on 5 August 2026 the MPC held the repo rate at 5.25% in a unanimous vote, the fourth consecutive pause of the year after decisions in February, April, June and August 2026, with the Standing Deposit Facility at 5.00% and the Marginal Standing Facility at 5.50%. The stance was left neutral, and the committee revised its FY 2026-27 projections to 6.7% GDP growth and 5.0% CPI inflation. Any move at the October meeting feeds directly into the external-benchmark loan rates that composition dealers rely on for working capital, so the outcome, published on rbi.org.in, belongs on the watchlist.

The repo rate matters to a small trader well beyond the headline. A cash-credit or overdraft line priced at repo plus a spread reprices within roughly three months of any MPC change, so the 5.25% level held on 5 August 2026 is the reference point for a dealer's borrowing cost through the CMP-08 quarter. For those with surplus after paying their October tax, the same rate environment shapes what a systematic investment plan can earn - our SIP calculator and lumpsum calculator let a dealer model a monthly deployment of retained profit at assumed return rates.

The two GST rows in that table are the standing monthly cadence rather than any special notification, and they are listed so composition dealers can see how their single quarterly date compares with the regular scheme's twin monthly filings. The composition scheme's whole appeal is that it collapses that monthly workload into four CMP-08 statements a year.

Earnings

There are no company earnings confirmed in the editorial calendar for the immediate window, so this section names none - inventing a results date would breach the zero-hallucination rule this desk works to. What composition dealers do declare every quarter is their own "earnings": CMP-08 is a self-assessment of turnover, and the tax is a flat percentage of that figure rather than a margin-based computation. Getting the rate right is the whole exercise.

The base on which these rates apply also differs by category. A manufacturer or trader pays 1% on the turnover of taxable supplies in the state, while the 5% and 6% rates apply on total turnover. A trader with Rs 40 lakh of turnover in the Jul-Sep 2026 quarter therefore reports Rs 40,000 of tax on the CMP-08 due 18 October 2026, split Rs 20,000 CGST and Rs 20,000 SGST. Because the levy is a flat percentage rather than a margin computation, the composition scheme shares the spirit of presumptive taxation, where turnover, not profit, drives the number.

Eligibility is capped by turnover, and crossing the ceiling is the event that ends composition status mid-year. The goods scheme caps aggregate turnover at Rs 1.5 crore, reduced to Rs 75 lakh for specified special-category states. Service providers who opted in under Section 10(2A) are capped at Rs 50 lakh. A dealer who breaches the ceiling during the year must move to the regular scheme and start filing monthly - which is why quarterly turnover self-assessment on CMP-08 is also an early-warning signal, not just a payment.

The cost of missing 18 October 2026

Interest under Section 50 of the CGST Act, 2017 accrues at 18% per annum on any tax paid after the 18 October 2026 deadline, computed for the exact number of days of delay. On a Rs 40,000 quarterly liability, 18% per annum works out to roughly Rs 20 a day, so a 30-day slip adds around Rs 600 of avoidable interest. The self-assessed tax itself does not lapse or reduce, so the only variable a dealer controls is time. Composition dealers should also note that a track record of on-time CMP-08 filing feeds into the compliance rating that counts when the annual GSTR-4 for FY 2026-27 falls due on 30 June 2027.

For a dealer with cash to spare after clearing the October tax, the discipline of a fixed quarterly outflow pairs naturally with a fixed monthly investment. A dealer who sets aside a rising amount each year can model it with our step-up SIP calculator, which escalates the monthly contribution in line with a growing business. The broader point is that the composition scheme trades a lighter compliance load for a flat levy, and the 18th of the month after each quarter is the single date that keeps the arrangement intact.

FAQ

What is the CMP-08 due date for the July-September 2026 quarter?

Form GST CMP-08 for the quarter July to September 2026 must be filed and the self-assessed tax paid by 18 October 2026. The rule is fixed: the statement is due on the 18th of the month succeeding each quarter.

Who has to file CMP-08?

Every taxpayer registered under the composition levy of Section 10 of the CGST Act, 2017 must file CMP-08. This covers dealers who registered as composition taxable persons through Form GST REG-01 and existing taxpayers who opted in through Form GST CMP-02.

What are the composition tax rates?

Traders and manufacturers pay 1% of turnover (0.5% CGST plus 0.5% SGST), restaurant services pay 5% (2.5% plus 2.5%), and other service providers under Section 10(2A) pay 6% (3% plus 3%). The rate is applied to turnover, not to profit.

What happens if I file CMP-08 late?

Interest runs at 18% per annum under Section 50 of the CGST Act, 2017 on the tax paid after 18 October 2026, calculated for the number of days of delay. The self-assessed liability does not go away, so the cost only rises with time.

Is CMP-08 the same as the GSTR-4 annual return?

No. CMP-08 is a quarterly statement-cum-challan used to pay tax four times a year. GSTR-4 is the single annual return, due by 30 June following the close of the financial year - 30 June 2027 for FY 2026-27 - that reconciles the full year's figures.

What turnover disqualifies a business from the composition scheme?

The goods composition scheme caps aggregate turnover at Rs 1.5 crore, reduced to Rs 75 lakh in specified special-category states. Service providers under Section 10(2A) are capped at Rs 50 lakh. Crossing the ceiling in-year means shifting to the regular scheme and filing monthly returns.

Does a composition dealer need to file anything else in the same window?

Beyond CMP-08 on 18 October 2026, the only other composition-scheme obligation is the annual GSTR-4, due 30 June following the financial year. Composition dealers do not file the monthly GSTR-1 or GSTR-3B that regular taxpayers file on the 11th and 20th of each month.