Section 31 of CGST Act Explained: Tax Invoice Requirements & Timing

Section 31 of CGST Act Explained: Tax Invoice Requirements & Timing

A tax invoice is more than a bill — under GST, it is the legal document that triggers tax liability, enables the recipient to claim input tax credit, and forms the backbone of the entire return-filing and matching ecosystem. Section 31 of the CGST Act, 2017 lays down when a registered person must issue a tax invoice, what it must contain, and the special timing rules for goods versus services, continuous supplies, and reverse charge transactions.

Because invoicing errors cascade downstream — affecting both the supplier's tax liability and the recipient's ability to claim ITC under Section 16 — getting Section 31 right is one of the most operationally important parts of GST compliance. This article explains the section in plain terms; as always, treat time limits, formats, and thresholds mentioned here as indicative and verify the current position before relying on them.

What Section 31 of the CGST Act says

Section 31 requires every registered person supplying taxable goods or services to issue a tax invoice showing the description, quantity, value of goods or services, tax charged, and other prescribed particulars, before or at the time specified in the section.

For goods, the section generally requires the invoice to be issued:

• Before or at the time of removal of goods for supply, where the supply involves movement of goods, or
• Before or at the time of delivery of goods or making them available to the recipient, in other cases.

For services, the section generally requires the invoice to be issued before or after the provision of service, but within a prescribed period from the date of supply of service (commonly understood to be a specified number of days — verify the current limit, as it may differ for certain classes of taxpayers such as banks and financial institutions, which may have a longer prescribed period).

Section 31 also addresses several special situations:

• Continuous supply of goods — where successive statements of accounts or successive payments are involved, the invoice must generally be issued before or at the time each statement is issued or payment is received.
• Continuous supply of services — where the contract provides for periodic payment, invoices are generally tied to the due date of payment as per the contract, or the date of actual payment, or the date of completion of an event to which payment is linked, depending on the facts.
• Goods sent on approval basis — invoices must generally be issued at the time the supply is deemed to take place, or a prescribed period from the removal of goods, whichever is earlier.
• Reverse charge supplies from unregistered persons — the recipient, being liable to pay tax, is generally required to issue an invoice on the date of receipt of goods or services, since the unregistered supplier cannot issue a GST-compliant tax invoice.
• Continuing services that cease before completion — an invoice must generally be issued at the time the supply ceases, to the extent of the supply made before cessation.
• Cases where the value of supply is below a prescribed threshold and the recipient is unregistered — a tax invoice may not be mandatory unless the recipient specifically requests one, though a consolidated invoice or bill of supply mechanism may apply instead.

The section also empowers the government to prescribe the manner, particulars, and categories of documents (like bill of supply for exempt supplies or composition taxpayers, and other prescribed documents such as receipt vouchers, refund vouchers, and payment vouchers for reverse charge) through rules — so the granular formatting requirements sit in the CGST Rules rather than the section itself, and should be checked separately.

Who it applies to

Section 31 applies to:

• Every registered person supplying taxable goods or services, who must issue a tax invoice for each such supply.
• Registered persons receiving supplies from unregistered persons under reverse charge, who must self-issue an invoice since the unregistered supplier cannot.
• Businesses with continuous supply arrangements, such as annual maintenance contracts, subscription services, construction contracts with milestone billing, or utility supplies.
• Composition scheme taxpayers, who issue a "bill of supply" instead of a tax invoice, since they cannot charge GST separately.
• Suppliers of exempt goods or services, who similarly issue a bill of supply rather than a tax invoice.
• E-commerce operators and businesses issuing e-invoices, where applicable, subject to separate e-invoicing rules for businesses above a prescribed turnover threshold (verify the current applicability threshold).

Key provisions

The essential operative rules under Section 31 are:

1. Timing for goods — invoice issued at or before removal/delivery, depending on whether movement is involved.
2. Timing for services — invoice issued within a prescribed number of days from the date of supply of service, with a possibly different (often longer) period for specified sectors like banking and insurance — verify current limits.
3. Continuous supply rules — invoice timing tied to statement of accounts, contractual payment due dates, or actual payment, depending on whether it is goods or services.
4. Reverse charge self-invoicing — recipients liable under reverse charge from unregistered suppliers must issue their own invoice and, in many cases, a payment voucher at the time of payment to the supplier.
5. Bill of supply for exempt/composition supplies — a simplified document without tax charged, replacing the tax invoice where GST is not separately chargeable.
6. Receipt and refund vouchers for advances — where advance payment is received for a supply, a receipt voucher is generally required, and if the supply does not eventually take place, a refund voucher.
7. Revised invoices — registered persons can issue revised invoices against invoices already issued during the period between the effective date of registration and the date of grant of registration certificate.
8. Prescribed particulars — invoices must contain specific fields such as GSTIN of supplier and recipient (where registered), invoice number and date, description, HSN/SAC code, quantity, taxable value, tax rate, and tax amount, along with signature — the exact list of mandatory fields is prescribed under the rules and should be verified against the current format requirements.

Practical example

Consider a company that manufactures and sells goods that require transportation to the buyer's location. Because the supply involves movement of goods, Section 31 requires the tax invoice to be issued before or at the time the goods are removed from the factory for delivery — not after the goods reach the customer. If the company waits until the customer confirms receipt to raise the invoice, it would technically be non-compliant with the timing requirement, even if the tax is eventually paid correctly.

In a services example, an IT consulting firm providing a one-time project-based service would generally need to issue its invoice within the prescribed number of days from completion of the service. But if the same firm has an annual retainer contract with monthly payments due on a fixed date each month, it falls under continuous supply of services, and the invoice timing would instead be linked to that contractual due date, regardless of whether work was actually performed that exact month.

How to comply

To stay compliant with Section 31, businesses should generally:

• Map each type of supply (goods with movement, goods without movement, one-time services, continuous services) to the correct invoice timing rule, rather than applying a single default practice across the board.
• Automate invoice generation at the point of dispatch or delivery for goods, ideally integrated with the e-way bill and dispatch process, to avoid manual timing errors.
• Track contractual payment due dates carefully for continuous supply arrangements, since invoice timing is often tied to the contract rather than actual service delivery.
• Issue self-invoices and payment vouchers promptly for reverse charge transactions with unregistered suppliers, since this is often overlooked.
• Use the correct document type — tax invoice, bill of supply, receipt voucher, or refund voucher — based on the nature of the transaction and registration status.
• Ensure all mandatory particulars are present, including correct HSN/SAC codes, GSTIN, and sequential invoice numbering, since incomplete invoices can jeopardise the recipient's ITC claim under Section 16.
• Comply with e-invoicing requirements if turnover crosses the applicable threshold, including generating invoice reference numbers (IRN) through the government portal before the invoice is treated as valid for specified purposes.
• Reconcile invoice dates with return filing periods to ensure tax is reported in the correct tax period, since invoice timing directly determines the time of supply and tax liability.

Penalties/consequences (hedged)

Failure to issue an invoice, issuing an incorrect invoice, or failing to account for it properly generally attracts consequences such as:

• A general penalty for contravention of GST provisions where no specific penalty is separately prescribed, which is typically expressed as a monetary amount or a percentage of tax involved, subject to a minimum and maximum — verify current figures.
• Denial of input tax credit to the recipient if the invoice is invalid, incomplete, or does not match reporting requirements, indirectly harming business relationships even if the supplier alone was at fault.
• Interest liability on delayed tax payment where the invoice timing error results in tax being reported in a later period than required.
• In cases of deliberate non-issuance of invoices to evade tax, more severe consequences including higher penalties and potential proceedings under provisions dealing with tax evasion.
• Under e-invoicing rules, an invoice without a valid IRN (where e-invoicing applies) may be treated as not a valid tax invoice for certain purposes, again affecting downstream ITC.

Because monetary penalty amounts and thresholds are periodically revised, please verify the current figures against the latest CGST Act and CBIC notifications before assessing exposure.

Recent changes (hedge)

Invoice-related rules under GST have evolved significantly since 2017 — most notably through the phased rollout of mandatory e-invoicing, which started with larger taxpayers and has progressively been extended to lower turnover thresholds over successive years. Time limits for reporting e-invoices to the Invoice Registration Portal have also been tightened for certain categories of taxpayers in various notifications.

Because e-invoicing applicability thresholds, reporting time limits, and invoice format requirements (particularly around HSN code digit requirements) have changed multiple times, businesses should verify the current threshold and procedural requirements applicable to their turnover and sector before assuming last year's compliance approach still holds.

Common mistakes

Frequent errors businesses make around Section 31 include:

• Issuing invoices late for goods, especially raising the invoice only after delivery confirmation rather than at removal.
• Missing the invoice timing window for services, particularly for one-off consulting or professional services with informal billing practices.
• Misapplying continuous supply rules, by treating milestone-based contracts as one-time supplies or vice versa.
• Failing to self-invoice for reverse charge purchases from unregistered vendors, especially for services like legal fees, transport, or rent from unregistered landlords.
• Omitting mandatory invoice particulars, such as incorrect or missing HSN/SAC codes, which can affect both supplier compliance and recipient ITC.
• Not generating e-invoices/IRNs where applicable, especially as thresholds have been lowered over time, catching mid-sized businesses off guard.
• Using the wrong document type, such as issuing a tax invoice instead of a bill of supply for exempt or composition supplies.
• Not issuing receipt vouchers for advances, particularly in service industries where advance payments are common.

FAQ

What is Section 31 of the CGST Act?

Section 31 specifies when a registered person must issue a tax invoice for a supply of goods or services, and empowers rules prescribing the invoice's contents and related documents like bills of supply and payment vouchers.

When should a tax invoice be issued for goods?

Generally before or at the time of removal of goods, where the supply involves movement, or before or at the time of delivery in other cases. Please verify any sector-specific variations.

When should a tax invoice be issued for services?

Generally within a prescribed number of days from the date of supply of service, though the exact number of days should be verified as it may differ for certain regulated sectors like banking.

What is a bill of supply and who issues it?

A bill of supply is issued instead of a tax invoice by composition scheme taxpayers and suppliers of exempt goods or services, since these suppliers cannot charge GST separately on the invoice.

Do I need to issue an invoice for reverse charge purchases from unregistered suppliers?

Yes, generally the recipient liable to pay tax under reverse charge must self-issue an invoice on the date of receipt of goods or services, along with a payment voucher at the time of payment.

What happens if I don't issue an invoice on time?

It can result in a general penalty for contravention of GST provisions, interest on any resulting delay in tax payment, and potential denial of input tax credit to the recipient — please verify current penalty amounts.

Is e-invoicing mandatory for all businesses?

No, e-invoicing generally applies only to businesses above a specified turnover threshold, and this threshold has been lowered progressively over the years — verify the current applicability threshold for your business.

What details must a tax invoice contain?

Prescribed particulars generally include supplier and recipient GSTIN (where applicable), invoice number and date, description of goods/services, HSN/SAC code, quantity, taxable value, applicable tax rate and amount, and signature — the exact list is set out in the CGST Rules and should be verified for completeness.

Legal Suvidha's GST team handles this — setting up compliant invoicing workflows, e-invoicing integration, and reverse-charge documentation so businesses don't lose ITC or face penalties over invoicing technicalities.

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