Add GST to a base price, or remove GST from a total that already includes it. Enter the amount and rate — base, GST and total appear at once.
Your total is 1.15× the amount before GST. Use this total for a GST-added quote or invoice.
Type the price before GST, or the final total that already includes it.
Enter the GST rate, then choose Add GST or Split GST from total to match that starting figure.
Read base, GST and total. Copy if you need the figures elsewhere.
Same 10% rate. Two starting figures. Pick the direction that matches the amount you already have.
Generic worked examples, not customer results.
A generic service quote starts with a price before GST.
Input: $200.00 before GST at one 10% GST rate.
Output: GST = $20.00; total = $220.00.
Why: GST is 10% of the before-tax amount, so $200.00 × 10% produces $20.00.
Use: Use this breakdown when preparing a quote or invoice that starts before GST.
Boundary: This arithmetic assumes one rate applies to the whole amount; calculate mixed-rate lines separately.
A generic receipt or displayed price already includes GST.
Input: $220.00 total at one 10% GST rate.
Output: Before GST = $200.00; GST = $20.00.
Why: Divide $220.00 by 1.10 to reverse the increase. Subtracting 10% directly gives $198.00, which is not the original before-GST amount.
Use: Use this split to check a receipt or a GST-inclusive displayed price.
Boundary: This arithmetic assumes one rate applies to the whole amount; check each mixed-rate line separately.
Multiply the base price by the GST rate divided by 100 to find the GST, then add it to the base price. For example, $100 at 10% GST gives $10 GST and a $110 total.
Divide the GST-inclusive total by 1 plus the GST rate as a decimal. At 10%, divide by 1.10. The result is the base price; subtract it from the total to find the GST component.
GST is calculated from the base price, not the final total. Directly subtracting the percentage from a GST-inclusive total gives the wrong base. Use division, or open the Reverse GST Calculator for the complete backwards-calculation workflow.
You can enter any non-negative GST rate. Replace the starting value with the rate that applies to your transaction; rates and exceptions vary by jurisdiction and can change, so confirm the current rate with the relevant tax authority.
GST exclusive means the starting price does not include GST, so tax must be added. GST inclusive means the final price already contains GST, so the base and tax must be separated.
It keeps unrounded values during calculation and displays two decimal places. All results use the same currency as the amount you enter; no currency conversion occurs. Follow the source invoice and local rules for final rounding.
No. It performs the arithmetic for one GST rate at a time. Check the original transaction's rate, rounding, exemptions, invoice requirements and filing rules before relying on it for a return.
No. The calculation runs in your browser, and this homepage calculator does not store your amounts on a server.
Choose the calculator that matches your calculation direction, workflow, or tax task.
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