Reverse GST Calculator
Find the base price and the GST amount hidden inside a price that already includes GST.
- GST amount
- —
Arithmetic only, not tax advice.
What is the Reverse GST Calculator?
The reverse GST calculator takes a price that already includes GST and the rate you enter, then works backwards to the base price before tax and the GST amount inside it. Use it to read supplier bills, MRP-style prices or any tax-inclusive quote.
How it works
The base price is the GST-inclusive price divided by one plus the rate divided by 100. The GST amount is the inclusive price minus the base price. For example, 11,800 at an 18 per cent rate gives a base of 10,000 and GST of 1,800.
How to use it
- Enter the price that includes GST.
- Enter the GST rate that was applied.
- Read the base price and the GST amount.
Reverse GST Calculator — FAQ
Why not just subtract the rate percentage from the price?
Because GST is charged on the base price, not on the final price. Subtracting 18 per cent of the total gives a wrong, lower tax figure.
Where do I find the rate to type in?
Use the rate printed on your invoice or the current official rate for the item. This tool never assumes a rate for you.
Can I use it for any tax-inclusive price?
Yes. It works for any percentage added on top of a base price, such as service charges, as long as the percentage was applied to the base.