GST / tax calculator

Goods and Services Tax (GST), VAT and sales tax all add a percentage to the price of goods and services. Businesses need to add tax to a net price when invoicing, and extract the tax from a gross price when recording purchases. This calculator does both and shows the net, tax and gross amounts.

How to use it

1. Enter the amount.
2. Enter the tax rate, such as 5%, 12%, 18% or 28% for Indian GST, or 20% for UK VAT.
3. Choose whether the amount excludes or includes tax.
4. Read the net, tax and gross figures.

Formulas

• Add tax: Tax = Net × Rate / 100, Gross = Net + Tax.
• Remove tax: Net = Gross / (1 + Rate / 100), Tax = Gross - Net.

Worked examples

• Adding 18% GST to 10,000: tax 1,800, gross 11,800.
• Extracting 18% GST from 11,800: net = 11,800 / 1.18 = 10,000, tax 1,800.

A common mistake is to take 18% of 11,800 (2,124). That overstates the tax, because the 18% applies to the net price, not the gross.

Indian GST split

• Intra-state sale: tax is split equally into CGST and SGST. 18% GST = 9% CGST + 9% SGST.
• Inter-state sale: the full rate is charged as IGST.

Tips

• Round tax per invoice line or per invoice consistently, following local rules.
• Discounts given before supply reduce the taxable value.