GST Calculator
Add GST to a price, or work backwards to pull it out of a GST-inclusive total.
How to use the GST Calculator
- Enter the amount.
- Set your GST rate and choose add or remove.
- Read the net, the GST and the gross total.
Add: GST = net × rate% · Remove: net = gross ÷ (1 + rate%)
About the GST Calculator
This calculator handles GST in both directions. In add mode it applies GST = net x rate% to a tax-exclusive price and gives you the GST amount plus the gross total. In remove mode it works backwards from a GST-inclusive total using net = gross / (1 + rate%), then reports the tax that was baked into the price. The rate is entirely yours to set, so the tool never assumes any particular country figure.
The reverse calculation is the part people most often get wrong. To strip GST from a gross price you divide by one plus the rate, not multiply the gross by the rate. At 18%, a $118 inclusive price divides by 1.18 to give a $100 net and $18 of GST. Multiplying $118 by 18% would overstate the tax, so the division method is the correct one.
Enter your amount, set the rate, and choose add or remove to see the net, the GST, and the gross side by side. Because you control the percentage, the same tool works for any GST or sales-tax rate worldwide. For value-added tax elsewhere, use the VAT Calculator, or price a markup with the Markup Calculator.
Frequently asked questions
How do I add GST to a price?
Choose add mode, enter the net price, and set your rate. The tool multiplies the net by the rate to get the GST, then adds it on for the gross total. At 18%, a $100 net becomes $18 GST and a $118 gross.
How do I remove GST from an inclusive price?
Choose remove mode and enter the gross total. The calculator divides by one plus the rate to find the net, then shows the GST inside it. At 18%, $118 divides by 1.18 to give a $100 net and $18 of tax.
Why not just multiply the gross by the rate to find GST?
Because the gross already includes the tax, multiplying it by the rate overstates the GST. The correct reverse method divides the gross by one plus the rate to recover the true net, and the difference is the actual GST.
What GST rate does the tool use?
None by default beyond the starting value you can change. The rate field is fully editable, so you set whatever GST or sales-tax percentage applies in your country or situation. The tool makes no country-specific assumption.
Can I use this for other sales taxes?
Yes. Because you enter the rate yourself, the same add and remove maths works for any percentage-based sales tax or VAT. Just type in the correct rate for your region.