What do GSTR-1, GSTR-3B and CMP-08 each report?
GSTR-1, GSTR-3B and CMP-08 are three different returns that serve three different purposes under GST, and a Chennai business's obligations depend on which registration category it falls into. GSTR-1 reports the details of outward supplies, essentially every invoice a business has issued during the period, and this data flows through to the recipient's input tax credit. GSTR-3B is a summary return that consolidates outward supplies, input tax credit claimed, and the net tax payable, and it is the return through which actual tax payment is made. CMP-08 is a statement-cum-return filed by businesses registered under the composition scheme, reporting a simplified summary of turnover and the tax payable at the composition rate, rather than invoice-level detail.
These returns and their purpose are identical for a business in Chennai as for a business anywhere else in India, since GST return filing runs entirely through the national GST portal.
Monthly versus quarterly filing: the QRMP option
Not every business files GSTR-1 and GSTR-3B monthly. Smaller taxpayers below a turnover threshold set for this purpose can opt into the Quarterly Return Monthly Payment (QRMP) scheme, under which GSTR-1 and GSTR-3B are filed quarterly, while tax is still paid monthly through a simplified challan based on either the previous quarter's liability or actual liability for the month. This scheme is designed to reduce the compliance burden of monthly return filing for smaller taxpayers while keeping the exchequer's cash flow through monthly payments.
Whether a business should opt into QRMP or continue filing monthly depends on its transaction volume, how frequently its customers need invoice data reflected quickly for their own credit claims, and its internal bookkeeping rhythm. Because the eligibility threshold and scheme mechanics are revised periodically, businesses should confirm current eligibility on the GST portal before opting in or out for a financial year.
Composition scheme taxpayers, who file CMP-08, are on a quarterly cycle by design and follow a separate annual return process, since the composition scheme itself is meant for smaller taxpayers who pay tax at a fixed rate on turnover rather than claiming input tax credit.
Consequences of late or non-filing
Filing late or not at all under GST carries consequences that compound over time: late fees accrue for each day of delay, interest applies on any tax paid late, and a business's GST registration can eventually face suspension or cancellation for continued non-filing. Persistent non-filing also blocks a business's own ability to file subsequent returns in some cases, since certain returns are sequential, and it can affect the business's compliance rating as visible to customers and vendors. Because the exact late fee amounts, interest rates and cancellation triggers are set out in the GST law and revised periodically, this article does not quote figures — the safest approach is to check the current schedule on the GST portal and, more importantly, to avoid the situation by filing on time.
Beyond the direct cost, late filing has a second-order effect: a supplier's late or incorrect GSTR-1 filing can delay or block input tax credit for their own customers, which is a commercial relationship problem as much as a compliance one.
The reconciliation discipline that matters
Accurate, timely GST return filing depends on reconciliation happening continuously, not just at filing time. This means matching sales recorded in the business's own books against what is reported in GSTR-1, checking that input tax credit claimed in GSTR-3B matches what suppliers have actually reported (visible through GSTR-2B), and reconciling the annual figures against the books before the annual return is filed. A business that reconciles only at year-end, rather than each period, tends to discover mismatches, missing invoices or credit that needs reversal well after the fact, which is harder and sometimes costlier to correct.
For businesses on QRMP, reconciliation discipline matters even more, because the quarterly return consolidates three months of activity at once, and errors compound across that window before they surface.
What PNPC does
PNPC's Chennai office manages monthly and quarterly GST return filing for businesses across categories, including GSTR-1, GSTR-3B and CMP-08 for composition taxpayers. This includes assessing whether a business qualifies for and should opt into the QRMP scheme, preparing and filing returns within the applicable cycle, reconciling outward supply data and input tax credit against GSTR-2B before each filing, and flagging discrepancies for correction before they compound.
Engagement typically begins with a review of the business's current filing pattern and turnover to confirm the correct filing frequency and category, followed by a recurring monthly or quarterly filing and reconciliation cycle. Always check the official GST portal at gst.gov.in for current late fee schedules, interest rates and QRMP eligibility thresholds.
If your Chennai business needs its GST return filing brought current or wants a reconciliation review before the next cycle, contact PNPC's GST return filing team to get started.
Common mistakes businesses make with monthly and quarterly filing
A recurring issue PNPC sees is a business opting into QRMP for the reduced filing frequency without accounting for the monthly payment obligation that continues regardless, then treating the quarter as "nothing due" in the two months between GSTR-3B filings and getting caught out by the monthly challan deadline. Another common gap is a business that changes its scheme election, moving in or out of QRMP or composition, without updating its internal reconciliation calendar to match, so the team keeps working to the old filing rhythm for a period or two after the scheme has actually changed. Building the filing calendar around the business's current, confirmed scheme status, rather than an assumption carried over from a previous year, avoids most of these timing errors.
What is genuinely state-specific about GST in Tamil Nadu
GST is one law, but it is administered through state jurisdictions, and that is where the local detail lives. A Tamil Nadu registration carries state code 33 as the first two digits of the GSTIN, and the registration is allocated between the central and the Tamil Nadu authority - which determines which office raises queries, conducts scrutiny and hears you in an audit or assessment. A business operating from Chennai and another state needs a separate registration per state, with its own returns, its own input-tax pool and its own officer, so what looks like one compliance obligation is really several running in parallel. Chennai's base is weighted towards automotive and auto components, engineering and general manufacturing, textiles, and BFSI back-office operations, alongside heavy port-linked EXIM activity - so export incentives, customs interaction and factory-level compliance come up far more often here than in a services-only market, which shapes the issues that actually surface in Tamil Nadu scrutiny.