Most Indian freelancers and small business owners know they need to issue a GST invoice. Far fewer know the actual GST invoice rules that govern what goes on it, when it must be issued, and what happens if they get it wrong. There are two laws you need to know cold: Section 31 of the CGST Act 2017 (which tells you when to issue the invoice) and Rule 46 of the CGST Rules 2017 (which tells you what must be on it). Miss either one and you're exposed — to GST notices, ITC rejections for your client, and penalties that start at ₹10,000.
Arjun runs a UX design consultancy out of Koramangala, Bengaluru. He completed a ₹72,000 project for a client in Hyderabad in late March 2026. He was busy wrapping up the financial year and didn't get around to issuing the invoice until April 15 — 46 days after delivering the work. His accountant flagged it immediately. Under Section 31 of the CGST Act, service invoices must be issued within 30 days of supply. Arjun's invoice was 16 days late. His client's finance team refused to process ITC against it. Arjun had to issue a fresh invoice with a corrected date, refile GSTR-1, and explain the discrepancy in writing to his client's CA. Three weeks of back-and-forth to fix a deadline he didn't know existed.
The GST invoice rules aren't complicated once you know them. The problem is that nobody teaches them clearly — you either find out from a CA after something goes wrong, or you stumble across them in a 200-page government circular. Let me break them down properly.
What Are the GST Invoice Rules? The Two Laws That Matter
When people search for "gst invoice rules," they're really looking for two distinct sets of rules that work together:
The "When" Rule — Invoice Timing
Section 31 defines when a tax invoice must be issued. It sets hard deadlines based on whether you're supplying goods or services, and what type of business you're in. Violating Section 31 timing rules is treated as a failure to issue an invoice — which attracts penalties under Section 122 of the CGST Act.
The "What" Rule — Mandatory Fields
Rule 46 defines exactly which fields must appear on every GST tax invoice. There are 12 mandatory fields — miss any one of them and the invoice is legally non-compliant. Your client cannot claim Input Tax Credit against a non-compliant invoice, which makes it your problem, not just theirs.
Section 31 — GST Invoice Time Limits You Must Know
The GST invoice time limit under Section 31 is one of the most commonly violated rules — because most people don't know it exists until they've already broken it. Here's the complete breakdown:
| Type of Supply | Invoice Must Be Issued | Legal Reference |
|---|---|---|
| Goods — continuous movement | Before or at time of removal | Section 31(1)(a) |
| Goods — no movement | Before or at time of delivery | Section 31(1)(b) |
| Services — general | Within 30 days of service completion | Section 31(2) |
| Services — banking / NBFC / insurance | Within 45 days of service completion | Section 31(2) proviso |
| Continuous supply of services | On each payment due date or actual receipt | Section 31(5) |
| Reverse charge supply | Date of payment or 60 days from supplier invoice, whichever is earlier | Section 31(3)(f) |
⚠️ The 30-day rule catches freelancers constantly.
If you complete a service on March 31, your invoice must be dated no later than April 30. Not whenever you get around to billing. Not end of next quarter. 30 days from delivery — hard deadline. A late invoice is treated as a missing invoice for GST purposes.
Rule 46 — GST Invoice Mandatory Fields (Complete List)
Rule 46 of the CGST Rules 2017 lists every field that must appear on a compliant GST tax invoice. These are the GST invoice mandatory fields — not suggestions, not best practices. All 12 are legally required. Here's the full list with what each one means in practice:
| Rule 46 Field | What It Means in Practice | Common Mistake |
|---|---|---|
| Supplier name, address, GSTIN | Your registered business name and address exactly as in GST portal | Using trade name instead of legal name |
| Invoice number | Sequential, max 16 characters, unique within financial year | Restarting numbering mid-year or exceeding 16 chars |
| Invoice date | Date of issue — must comply with Section 31 time limits | Backdating invoices to avoid late issuance penalty |
| Buyer name, address, GSTIN | Registered details of the recipient — verified against GSTN | Using client's trade name or unverified GSTIN |
| Place of Supply | State code determining CGST+SGST vs IGST — not always billing address | Leaving blank or defaulting to supplier state |
| HSN / SAC code | HSN for goods, SAC for services — digit count depends on turnover | Using HSN code for services, or wrong digit count |
| Description of goods / services | Clear description — "professional services" alone is insufficient | Vague descriptions that don't match the supply |
| Quantity and unit | For services, quantity can be 1 and unit can be "job" or "project" | Leaving blank for service invoices |
| Taxable value | Pre-tax value — must match what was agreed, before discounts are applied | Showing final amount instead of pre-tax amount |
| GST rate and tax amount | Rate (%) and rupee amount for CGST+SGST or IGST separately | Showing only total tax without splitting by head |
| Total invoice value | Taxable value + all taxes — must be auto-calculated, not manual | Rounding errors that don't match tax calculations |
| Reverse charge declaration | "Whether tax is payable under reverse charge: Yes/No" | Field missing entirely from invoice — most common gap |
Every field above is non-negotiable under the new GST invoice rules. The gst invoice mandatory fields india mandates under Rule 46 are identical whether you're a sole proprietor or a private limited company — gst tax invoice rules make no exceptions based on business size. If you've ever wondered whether the gst invoice rules section 31 timing requirements and Rule 46 field requirements are linked — they are. A late invoice that's also missing mandatory fields compounds the penalty exposure. If your current template is missing even one field — particularly the Place of Supply or Reverse Charge declaration — fix it before your next invoice goes out. GSTInvoiceFree.in includes all 12 Rule 46 mandatory fields automatically.
GST Invoice Rules for Services vs Goods — Key Differences
The GST invoice rules for services differ from goods in ways that trip up freelancers and consultants specifically. Here's where the rules diverge:
| Rule | Goods | Services |
|---|---|---|
| Invoice timing | Before or at removal | Within 30 days of supply |
| Tax code type | HSN code mandatory | SAC code mandatory |
| Quantity field | Mandatory with unit of measure | Can show "1 Job" or "1 Project" |
| Place of Supply | Delivery location | Usually recipient's location (with exceptions) |
| Delivery challan required? | Yes, for goods in transit | No |
| Bill of Supply | For exempt goods only | For exempt services or unregistered supplier |
GST Invoice Cancellation Rules — What You Can and Cannot Do
You can't simply delete a GST invoice once it's been issued. The GST invoice cancellation rules require a formal paper trail — and the process differs depending on whether you're above or below the e-invoicing threshold.
For businesses below ₹5 crore AATO (most freelancers and small businesses):
Issue a credit note under Section 34 of the CGST Act referencing the original invoice number, date, and reason for cancellation. The credit note must be issued before the due date of the September GSTR-3B of the following financial year. Declare it in GSTR-1 under the credit note table.
For businesses above ₹5 crore AATO (e-invoice mandatory):
Cancel on the IRP portal within 24 hours of IRN generation. After 24 hours, cancellation on the portal is not possible — you must issue a credit note instead. The IRN itself cannot be amended after 24 hours under any circumstances.
GST Invoice Amendment Rules — Correcting Errors After Filing
Made a mistake on an already-filed invoice? The GST invoice amendment rules give you a window to fix it — but not indefinitely. Here's how amendments work:
- Amendments to B2B invoice details (buyer GSTIN, taxable value, tax amount) are done through the "Amendments to B2B invoices" table in GSTR-1 of any subsequent month.
- The amendment window closes at the due date of the September GSTR-1 of the following financial year — typically October 11. After that, no amendments are possible for that financial year.
- For e-invoices: the IRN cannot be amended. Cancel within 24 hours and reissue, or issue a credit note and fresh invoice after 24 hours.
- Amendments affect your client's GSTR-2B — their ITC gets updated automatically once you file the amended GSTR-1.
⚠️ Don't issue a "revised" invoice with the same number.
Some people issue a second invoice with the same number marked "Revised" — this creates a duplicate in the GSTN system. The correct process is always: credit note for the original + fresh invoice with a new sequential number.
5 GST Invoice Rule Violations That Trigger Notices
These aren't theoretical risks. These are the new GST invoice rules violations that GSTN's automated matching system actually catches and flags — sometimes months after the invoice was issued.
Issuing Invoices After the Section 31 Time Limit
Completing a service in March and invoicing in May is a Section 31 violation — you had 30 days. It's not a technicality. A late invoice is treated as a failure to issue an invoice, which means your client's ITC claim on that invoice is on shaky ground if ever scrutinised. The fix is simple: set a calendar reminder for 25 days after every project completion. Never let 30 days pass.
Non-Sequential Invoice Numbering Within a Financial Year
Your invoice series must be sequential and consistent within each financial year. Gaps are a red flag — if you go from INV/2026-27/004 to INV/2026-27/007, GSTN's system notices the gap. Gaps suggest cancelled invoices that weren't reported, or invoices issued outside the system. Some businesses also reset their numbering mid-year when they switch software — also a violation of the new GST invoice rules on numbering.
Wrong GSTIN on the Invoice — Supplier or Buyer
A single transposed digit in a GSTIN — either yours or your client's — means the invoice cannot be matched in the GSTN system. Your client's GSTR-2B won't show the ITC. They'll follow up with you. You'll need to issue a credit note and a corrected invoice. Verify every GSTIN on every invoice against the GST portal's taxpayer search before sending — it takes 30 seconds and prevents a two-week headache.
Showing Total Tax Instead of Splitting by Head
Rule 46 requires the tax breakup to show CGST and SGST separately (for intrastate) or IGST separately (for interstate). Showing only "GST: ₹9,000" without splitting by head is a Rule 46 violation — even if the total is mathematically correct. Worse, some invoices show both CGST+SGST and IGST on the same invoice — which is impossible. You charge one or the other, never both. The split is determined entirely by Place of Supply.
Using a Business Name That Doesn't Match GST Registration
Your invoice must show your legal name exactly as registered with GST — not your brand name, not your freelance trading name, not a shortened version. If your GST registration says "Arjun Kumar Design Studio" and your invoice header says "AK Design," the GSTN system may not match it to your GSTR-1 filing. Many freelancers register under their full legal name and invoice under a brand name — without realising the mismatch creates a compliance gap.
Why I Built GSTInvoiceFree.in
I got tired of seeing small creators and shopkeepers get bullied by complex software or expensive CAs just to generate a simple, legal piece of paper they need to get paid.
The GST invoice rules exist for a reason — they create a paper trail that makes the tax system work. But understanding those rules shouldn't require a law degree, and following them shouldn't require a ₹2,000/month subscription. GSTInvoiceFree.in bakes all the GST invoice requirements India mandates directly into the tool — Section 31 timing is your responsibility, but every Rule 46 mandatory field is handled automatically. You can't accidentally miss the Reverse Charge declaration or the Place of Supply, because they're always there.
📋 2026 E-Invoice Update — New GST Invoice Rules for Larger Businesses
Businesses with Annual Aggregate Turnover (AATO) above ₹5 crore must now generate e-invoices through the GSTN IRP portal before issuing to clients. The IRP validates the invoice JSON and returns an IRN (Invoice Reference Number) and a QR code — both must appear on the final invoice sent to the client.
Key new GST invoice rules under e-invoicing: the IRN must be generated before the invoice is shared; cancellation is only possible within 24 hours of IRN generation on the portal; amendments to IRN are not permitted. If your AATO is below ₹5 crore, these new rules don't apply to you — a compliant PDF invoice remains sufficient.
Quick Reference — GST Invoice Rules Summary
Section 31 — Invoice Timing
Goods: before or at removal | Services: within 30 days | Banking/NBFC: within 45 days
Rule 46 — Mandatory Fields
12 fields required: supplier GSTIN, invoice number (max 16 chars), date, buyer GSTIN, Place of Supply, HSN/SAC code, description, quantity, taxable value, tax split (CGST+SGST or IGST), total value, reverse charge declaration
Cancellation (Section 34)
Always via credit note — never delete. E-invoice: cancel on IRP within 24 hours of IRN generation.
Amendment
Via GSTR-1 amendments table. Window closes: September GSTR-1 due date of following financial year.
Penalty (Section 122)
Non-compliance: ₹10,000 or tax amount — whichever is higher.
Generate a GST Invoice That Follows Every Rule — Free
GSTInvoiceFree.in auto-includes all 12 Rule 46 mandatory fields — Place of Supply, Reverse Charge declaration, correct CGST/SGST/IGST split — in every invoice. No login. No software. Instant PDF.
→ Create Compliant GST Invoice FreeFrequently Asked Questions
What are the GST invoice mandatory fields in India?
Under Rule 46 of the CGST Rules 2017, every GST tax invoice must include 12 mandatory fields: supplier name, address and GSTIN; sequential invoice number (max 16 characters); invoice date; buyer name, address and GSTIN; Place of Supply (state code); HSN code (goods) or SAC code (services); description of goods or services; quantity and unit; taxable value; tax rate and amount split as CGST+SGST or IGST; total invoice value; and a reverse charge declaration. Missing any GST invoice mandatory fields makes the invoice non-compliant and blocks your client's ITC claim.
What is the GST invoice time limit under Section 31?
Under Section 31 of the CGST Act 2017, the GST invoice time limit is: for goods, before or at the time of removal; for services, within 30 days of supply completion; for banking and financial services, within 45 days. Issuing a service invoice more than 30 days after delivery is a Section 31 violation. The penalty under Section 122 is ₹10,000 or the tax amount — whichever is higher. The GST invoice time limit is one of the most commonly missed rules among freelancers and consultants.
What are the GST invoice cancellation rules?
GST invoice cancellation rules require you to issue a credit note under Section 34 — you cannot delete or void an invoice. The credit note must reference the original invoice number and date, state the reason, and be filed in GSTR-1 before the September due date of the following financial year. For e-invoices (businesses above ₹5 crore AATO), cancellation must happen on the IRP portal within 24 hours of IRN generation. After 24 hours, only a credit note is possible — the IRN itself cannot be cancelled or amended.
What are the GST invoice amendment rules?
GST invoice amendment rules allow corrections through GSTR-1 by using the "Amendments to B2B invoices" table in any subsequent month's return. You can amend buyer GSTIN, taxable value, tax amounts, and other details. The amendment window closes at the due date of the September GSTR-1 of the following financial year. For e-invoices, amendments to the IRN are not permitted — cancel within 24 hours or issue a credit note and fresh invoice after that. Your client's GSTR-2B updates automatically once you file the amended GSTR-1.
What are the GST invoice rules for services?
The GST invoice rules for services differ from goods in three key ways. First, you must issue the invoice within 30 days of service completion (45 days for banks). Second, you must use a SAC code — not an HSN code. Common SAC codes: 998314 for IT/software services, 998311 for management consulting, 998361 for advertising. Third, the quantity field can show "1 Job" or "1 Project" for services — it doesn't need a unit of measure the way goods do. All other Rule 46 mandatory fields apply equally to service invoices.