Tax amount = taxable amount × tax % ÷ 100, and grand total = taxable amount + tax.
Each figure is rounded to two decimals for display. The discount and the tax rate apply to the whole invoice, not to individual lines.
Worked Example: A Freelancer's Invoice
Item
Qty × Rate
Amount
Website design
1 × ₹40,000
₹40,000
Hosting and maintenance (months)
12 × ₹500
₹6,000
Logo design
1 × ₹8,000
₹8,000
Subtotal
₹54,000
Less 10% discount
− ₹5,400
Taxable amount
₹48,600
GST at 18%
₹8,748
Grand total
₹57,348
If the client is in the same state, the ₹8,748 is shown on the bill as ₹4,374 CGST plus ₹4,374 SGST; for a client in another state it is shown as ₹8,748 IGST.
Preparing a GST Tax Invoice
This tool gives you the numbers; a valid GST tax invoice also needs certain details. These include the supplier's name, address and GSTIN, a unique serial invoice number and date, the buyer's name and address (and GSTIN for business buyers), the HSN or SAC code and description of each item, the taxable value, the rate and amount of tax split into CGST, SGST or IGST, and the place of supply. The CBIC website lists the full requirements.
Items at different GST rates: the calculator applies one rate to the whole invoice. If one invoice has, say, ₹30,000 of services at 18% and ₹20,000 of goods at 5%, calculate each group separately and add the results: ₹35,400 + ₹21,000 = ₹56,400.
A discount shown on the invoice at the time of sale reduces the taxable value, which is why the calculator applies tax after the discount.
A business that is not registered under GST must not charge GST. Set the tax field to 0 to produce a bill of supply total.
Many businesses round the grand total to the nearest rupee and show the difference as a "round off" line.
Frequently Asked Questions
The discount is applied first to the subtotal to get the taxable amount, and then tax is calculated on that discounted amount - the same order most invoices follow.
Yes, enter your applicable GST rate (e.g. 18%) in the "Tax / GST" field. Note that this calculator shows a single combined tax amount rather than splitting it into CGST/SGST or IGST - use the GST Calculator if you need that breakdown.
Yes, both fields default to treating a blank or zero value as no discount or no tax applied.
Group the items by rate and run the calculator once for each group, then add the grand totals. On the final invoice, show the taxable value and tax for each rate separately, since GST returns report tax rate by rate.
TDS is deducted by the client when paying, not added to or subtracted on the invoice itself, and it is generally calculated on the amount excluding GST when GST is shown separately. The invoice should still show the full grand total; the client then pays it minus any TDS and issues you a TDS certificate.