GST Calculator
Add or remove GST from an amount at any tax rate, instantly.
Goods and Services Tax (GST) is a consumption tax applied at a set percentage on the sale of goods and services, and businesses regularly need to move between tax-exclusive and tax-inclusive amounts — quoting a net price before adding GST, or working backward from a GST-inclusive invoice total to find the underlying pre-tax amount.
This calculator handles both directions. In Add GST mode, enter a net (pre-tax) amount and rate to see the GST amount and the final gross total. In Remove GST mode, enter a gross (tax-inclusive) amount to back out exactly how much of it was GST and what the original net amount was — a common need when reconciling invoices or receipts that only show a final total.
The math is straightforward but easy to get backward under pressure: adding GST multiplies the net amount by the rate, while removing GST from a gross amount requires dividing by (1 + rate), not simply subtracting the percentage — a mistake that consistently produces a slightly wrong answer.
How to use GST Calculator
- 1
Choose add or remove
Pick whether you're starting from a pre-tax or tax-inclusive amount.
- 2
Enter the amount and rate
Input your amount and the applicable GST rate.
- 3
Read the breakdown
See the net amount, GST amount, and gross amount instantly.
Features
- Handles both adding and removing GST
- Works with any GST rate, not a fixed default
- Instant live calculation as you type
- Clear three-way breakdown: net, tax, and gross
Frequently asked questions
Common mistakes to avoid
- Subtracting the tax percentage directly from a gross amount instead of dividing by (1 + rate).
- Using the wrong GST rate for a mixed-rate invoice with multiple tax categories.
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