Sales Tax/GST Calculator
Add GST, VAT or sales tax to a price — or work out the tax hiding inside a tax-inclusive price.
What is the Sales Tax/GST Calculator?
Sales tax maths trips everyone up: adding 18% is easy, but working backwards from a tax-inclusive price is not (you cannot just subtract 18%). This calculator does both directions correctly.
It includes presets for GST slabs (5%, 12%, 18%, 28%), VAT at 20%, and a custom rate field for any other tax — and shows the net price, the tax amount and the gross price side by side.
How to use the Sales Tax/GST Calculator
- Enter the amount.
- Pick a preset rate or type a custom rate.
- Choose whether the amount already includes tax, or tax must be added.
- Read the price before tax, the tax amount and the total.
Key features
- Add-tax and remove-tax (inclusive) modes
- GST 5/12/18/28% and VAT 20% presets
- Any custom rate
- Net, tax and gross shown to 2 decimals
- Results update as you type
Frequently asked questions
How do I add GST to a price?
Choose “Add tax to the amount”, enter the price and rate (for example 18%), and the tool shows the tax amount and the final price including tax.
How do I find the tax inside a final price?
Choose “Amount already includes tax”. The calculator splits the total into the original price and the tax portion — the reverse GST calculation used on invoices.
Which rates are built in?
The common GST slabs of 5%, 12%, 18% and 28%, plus VAT 20% and a fully custom rate for any country or US state.
Is rounding handled?
Results are shown to two decimal places, matching how invoices and receipts are normally written.