GST Invoice Mandatory Fields — The Complete Checklist

A GST invoice is only valid if it carries a specific set of fields defined under GST invoicing rules — miss one and the invoice can be rejected during your buyer's input tax credit reconciliation or flagged in your own GSTR-1 filing. This checklist covers every mandatory field, the fields that only apply conditionally, and the ones people assume are required but aren't.

The core fields every GST invoice must have

These apply to essentially every tax invoice, regardless of what you sell:

• Supplier details — your legal business name, address, and GSTIN
• Invoice number — unique and sequential for the financial year
• Invoice date — the date of issue
• Recipient details — buyer's name and address, plus GSTIN if they're GST-registered (B2B)
• HSN or SAC code — HSN for goods, SAC for services, at the digit length your turnover requires
• Description, quantity, and unit — for each item or service line
• Taxable value — the value before tax, after any discount
• GST rate and amount — shown as CGST + SGST (intra-state) or IGST (inter-state)
• Place of supply — required whenever it's inter-state, or differs from the buyer's address
• Total invoice value — taxable value plus tax, in figures (and ideally in words for high-value invoices)
• Signature — of the supplier or an authorized representative, physical or digital

Fields that only apply in specific situations

A few fields are mandatory only when the transaction meets certain conditions:

• Buyer's name, address, and state — mandatory even for an unregistered (B2C) buyer once the invoice value crosses the prescribed threshold, regardless of whether they have a GSTIN.
• Delivery address — required as a separate field whenever goods are shipped to an address different from the billing address.
• Reverse charge indicator — a line stating whether GST on the supply is payable by the recipient under reverse charge, wherever that applies.
• Export invoice details — invoices for exports must additionally state whether tax is paid or the supply is made under a Letter of Undertaking (LUT), along with the shipping bill details where applicable.
• QR code and IRN — businesses above the e-invoicing turnover threshold must generate the invoice through the government's Invoice Registration Portal, which returns an IRN and QR code that must appear on the invoice copy issued to the buyer.

Fields people assume are mandatory but aren't

• Buyer's PAN — not required; GSTIN (which embeds the PAN) is what matters for registered buyers.
• Bank account details — useful for the buyer to pay you, but not a GST compliance requirement.
• A specific invoice template or logo placement — no fixed layout is prescribed; only the field list is mandated.
• Terms and conditions or payment due date — good business practice, not a GST field.

Including these is harmless and often helpful for your client relationship — just don't treat their absence as a compliance issue, and don't let chasing them distract from the fields that are actually mandatory.

Worked example: checklist applied to a real invoice

A design agency in Mumbai invoices a registered client in Mumbai (intra-state) for ₹80,000 of website design work:

Every row in this table maps directly to a mandatory field — if any one of them were missing, the invoice would be incomplete even though the tax math is correct.

Common mistakes with mandatory fields

• Leaving place of supply blank on inter-state invoices — this is what determines CGST/SGST vs IGST, so it can't be inferred later if omitted.
• Truncating the GSTIN — a 15-character GSTIN entered incorrectly (even by one digit) invalidates the buyer's input tax credit claim.
• Using the wrong HSN/SAC digit length — check your required digit length against your turnover slab rather than copying a code you've seen elsewhere.
• Forgetting the reverse charge line on supplies where it applies — a small omission that shifts the compliance burden incorrectly.

If you haven't nailed down the step-by-step invoice creation process itself, start with how to create a GST invoice step-by-step, which walks through building the invoice from scratch. For the HSN/SAC field specifically, see how to find your HSN code as a freelancer. To see how this checklist translates into an actual invoice layout, see the GST invoice format explained, which includes a downloadable sample.

Let the fields fill themselves in

Tracking every mandatory and conditional field by hand across every invoice is where most compliance slips happen. The GST Invoice Generator includes every required field by default — GSTIN, HSN/SAC, place of supply, and the correct CGST/SGST/IGST split — so nothing gets left blank.

For agencies issuing these at volume, see Dharayana plans to save recurring client and field details so each new invoice starts pre-filled and compliant.

Frequently asked questions

What are the mandatory fields on a GST invoice?

Supplier name/address/GSTIN, a unique sequential invoice number and date, recipient details (GSTIN if registered), HSN/SAC code, description/quantity/ unit of goods or services, taxable value, GST rate and amount split into CGST/SGST or IGST, place of supply, and the total invoice value. A few conditional fields apply depending on the transaction — reverse charge, delivery address, and unregistered-buyer details above a value threshold.

Is a signature required on a GST invoice?

Yes, in general — a physical or digital signature of the supplier or an authorized representative is required. Invoices generated through the e-invoicing system carry a digitally signed QR code and IRN from the government portal, which is treated as meeting this requirement.

Do I need the buyer's address on every GST invoice?

Always for B2B invoices, since the buyer's GSTIN and address establish their input tax credit claim. For B2C invoices below the prescribed value threshold, buyer name and address aren't mandatory, but you must capture them above that threshold.

What is "place of supply" and why does it matter on the invoice?

Place of supply is the state where the transaction is deemed to occur for GST purposes. It determines whether you charge CGST/SGST or IGST, and it must be shown separately on the invoice whenever it differs from the buyer's billing address, such as inter-state supplies.

Is an HSN/SAC code mandatory on every invoice regardless of invoice value?

The code itself is mandatory once you're GST-registered, but the required digit length (4, 6, or 8 digits) depends on your aggregate turnover in the preceding financial year, not on the value of the individual invoice.

Ready to stop double-checking fields by hand? Try the GST Invoice Generator — every mandatory field is built in, free and with no login required.