This calculator switches between adding GST to a net (GST-exclusive) amount and removing GST from a GST-inclusive price, at any rate you enter. It shows the net amount, the GST portion, and the gross total — useful for invoicing, pricing, and working out the tax already baked into a price across GST countries like Australia, New Zealand and Singapore.
How it works
Pick a direction and enter the amount and rate:
- Add GST (exclusive → inclusive):
GST = net × rate ÷ 100,gross = net + GST. At 10%, gross = net × 1.10. - Remove GST (inclusive → exclusive):
net = gross ÷ (1 + rate ÷ 100),GST = gross − net. At 10%, net = gross ÷ 1.10.
The key subtlety is in Remove mode: the GST is not the rate times the inclusive price, because the rate applies to the net. You divide by (1 + rate) first, then take the difference.
Example
A GST-inclusive price of $110 at a 10% rate, in Remove mode:
- net = 110 ÷ 1.10 = $100.00
- GST = 110 − 100 = $10.00
In Add mode, a net $100 at 10% gives $10 GST and a $110 gross.
| Direction | Input | Rate | Net | GST | Gross |
|---|---|---|---|---|---|
| Add | $100 net | 10% | $100 | $10 | $110 |
| Remove | $110 gross | 10% | $100 | $10 | $110 |
GST rates by country
The tool works with any rate you enter. Common GST rates:
| Country | Rate | Notes |
|---|---|---|
| Australia | 10% | Standard rate; some items are GST-free (fresh food, medical) |
| New Zealand | 15% | Broad-based, few exemptions |
| Singapore | 9% | Raised from 8% in 2024 |
| India | 5%, 12%, 18%, 28% | Multiple rates depending on goods/services category |
| Canada | 5% federal GST | Provinces add HST/PST on top |
Common mistakes when calculating GST
Taking the rate of the inclusive price. This is the most frequent error. At 10%, GST is not 10% of $110 — that gives $11, which overstates the tax by $1. The correct calculation is $110 ÷ 1.10 = $100 net, so GST = $10. The rate always applies to the net, not the gross.
Confusing GST-free and GST-exempt. In Australia these are legally distinct categories with different treatment for input tax credits, but both result in zero GST on the supply. The calculator does not handle this distinction — it calculates GST at the rate you enter.
Rounding mid-calculation. Always carry full decimal precision until the final step. Rounding the net to the nearest cent before subtracting to find GST can introduce a rounding error that does not match the tax invoice. The calculator maintains full precision and rounds only for display.
All maths runs locally in your browser — your figures are never uploaded.