Invoice Calculator Guide: Line Items, GST & Invoice Totals
A well-built invoice is the foundation of professional business. Here's how to structure an invoice, calculate totals correctly with GST, and ensure legal compliance.
Invoice Calculation Structure
| Item | Qty | Rate | Amount |
|---|---|---|---|
| Web design | 1 | ₹15,000 | ₹15,000 |
| SEO services | 3 months | ₹5,000 | ₹15,000 |
| Hosting setup | 1 | ₹3,000 | ₹3,000 |
| Subtotal | ₹33,000 | ||
| GST @ 18% (CGST 9% + SGST 9%) | ₹5,940 | ||
| Total Payable | ₹38,940 | ||
CGST vs SGST vs IGST
Frequently Asked Questions
What information must be on an invoice?
A valid invoice typically needs: supplier name, address, and GSTIN; buyer name and address; invoice number and date; itemised list of goods/services with HSN/SAC codes; rate and amount; applicable GST (CGST + SGST or IGST); total payable; payment terms and bank details. For international: also add currency, country codes, and shipping terms.
What is the difference between a tax invoice and a bill of supply?
A tax invoice is issued when GST is applicable (registered seller to buyer). A bill of supply is issued by composition dealers or for exempt goods/services where no GST is charged. GST-registered businesses must issue a tax invoice for all taxable supplies.
How do I calculate invoice total with GST?
Total = Subtotal + GST. Subtotal = sum of (quantity × unit price) for all line items. For 18% GST on ₹10,000: GST = ₹1,800, Total = ₹11,800. For intra-state: split GST into CGST (9%) + SGST (9%). For inter-state: charge IGST (18%).
What is a pro forma invoice?
A pro forma invoice is a preliminary invoice sent before delivery — it shows what will be charged but is not a demand for payment. Used to confirm order details, for customs purposes on imports, and to help buyers arrange funding before the actual invoice is issued.
How long should I keep invoices?
In India, GST records (including invoices) must be kept for 72 months (6 years) from the due date of the annual return. Income tax records must be kept for 6 years from the end of the relevant assessment year. Keep digital copies as backup.
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