What is a GST Invoice?
A GST invoice is a legal document issued by a GST-registered business to its customer for goods or services supplied. Under the CGST Act 2017, every registered supplier must issue a tax invoice containing specific mandatory fields. Without a valid GST invoice, your customer cannot claim Input Tax Credit (ITC) — making proper invoicing critical for B2B transactions.
Mandatory Fields in a GST Invoice
Your GST invoice must include: (1) Name, address, and GSTIN of supplier; (2) Invoice number and date; (3) Name, address, and GSTIN of recipient (for B2B); (4) HSN/SAC code for each item; (5) Description, quantity, and value of goods/services; (6) Tax rate and tax amount (CGST/SGST or IGST); (7) Place of supply (state); (8) Signature of authorised person. Missing any of these can make your invoice invalid for ITC claims.
CGST vs SGST vs IGST — Which Applies?
The type of GST depends on whether the transaction is within the same state (intra-state) or across states (inter-state). If supplier and customer are in the SAME state: you charge CGST (Central GST) + SGST (State GST), each at half the applicable rate. For 18% GST, that's CGST 9% + SGST 9%. If supplier and customer are in DIFFERENT states: you charge IGST (Integrated GST) at the full rate. For 18% GST, that's IGST 18%. On a ₹10,000 invoice with 18% GST — same state: CGST ₹900 + SGST ₹900 = ₹1,800 tax. Different state: IGST ₹1,800.
Invoice Types You Need to Know
Tax Invoice: Standard invoice for GST-registered businesses for taxable supplies. Quote/Proforma: Estimate document — not a legal invoice, but can be converted to one when the deal is confirmed. Credit Note: Issued when you need to reduce the value of a previously issued invoice (refund or correction). Bill of Supply: Used by composition dealers or for exempt supplies where no GST is charged. Receipt Voucher: When you receive advance payment before supply.
How to Create a GST Invoice for Free
Option 1 — Techfied Invoicer (Recommended for Indian businesses): Go to invoicer.techfied.in and register free. Set your business profile with GSTIN and state. Click 'New Invoice', add your customer's details and state — CGST/SGST or IGST is calculated automatically. Add line items (or dictate them by voice). Choose one of 6 professional templates. Click 'Create & Send' — PDF is emailed instantly with a UPI payment link. Free plan includes 10 invoices/month. Option 2 — Excel/Word Templates: Download a free GST invoice template online. You must manually calculate CGST/SGST/IGST. Error-prone and time-consuming for high volumes.
Common GST Invoice Mistakes to Avoid
Wrong state for customer: Always verify the customer's billing state — wrong state means wrong tax type (CGST/SGST vs IGST). Missing HSN/SAC code: Mandatory for all goods and services. Wrong HSN codes can attract notices. Invoice number not sequential: GST invoices must be in a running serial number within a financial year. Not mentioning 'Tax Invoice': The document must clearly say 'Tax Invoice' at the top. Incorrect GSTIN: Always double-check the 15-digit GSTIN — wrong GSTINs invalidate ITC claims.
GST Rate Reference for Common Services
0%: Educational services, healthcare, exports. 5%: Packaged food, transport, restaurant (without AC). 12%: Processed food, computers, some IT services. 18%: Most professional services (IT, consulting, design, marketing), restaurants (with AC), electronics. 28%: Luxury goods, automobiles. When in doubt about your HSN/SAC code and applicable rate, consult your CA — wrong rates can result in GST notices.