business calculator
Add or remove GST from any amount instantly using a custom tax rate to calculate accurate pre-tax and tax-inclusive prices for free.
To add GST, multiply the pre-tax amount by (1 + rate). To remove it, divide the tax-inclusive amount by (1 + rate). At 10%, $100 becomes $110, and $110 divided by 1.1 returns $100 with $10 of GST. Subtracting 10% from $110 would give $99 and understate the pre-tax price, which is the error that most often breaks an invoice reconciliation.
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Total amount
$110
Tip
Save this page to quote customers, prepare invoices, and isolate GST components from all-inclusive prices quickly.
Summary
GST Total Amount
$110
GST Tax Component
$10
Pre-Tax Net Price
$100
GST Rate
10.00%
Breakdown
Compare the base pre-tax amount with the GST component.
| Item | Value |
|---|---|
| Base Pre-Tax Price | $100 |
| GST Component | $10 |
Comparison
Summary of GST base price, tax amount, and inclusive total.
| Item | Value |
|---|---|
| Pre-Tax Net | $100 |
| GST Tax | $10 |
| Total Gross | $110 |
Guide
Goods and Services Tax (GST) is a broad-based consumption tax applied to most goods and services. Like VAT, it is generally collected by businesses and remitted to the government. GST systems can be tax-exclusive or tax-inclusive, depending on local pricing conventions and invoice rules.
For commercial planning, the most important task is distinguishing whether a quoted figure already includes GST or whether GST must be added on top.
If the amount is tax-exclusive, add GST using:
Total Amount = Base Amount × (1 + (GST Rate) / 100)
GST Amount = Base Amount × (GST Rate) / 100
If the amount is tax-inclusive, recover the net amount using:
Pre-Tax Amount = (Gross Amount) / (1 + (GST Rate) / 100)
GST Amount = Gross Amount - Pre-Tax Amount
These equations make GST isolation easy whether you start from a sticker price or a vendor quote.
A common practical issue is whether the customer sees GST included in the listed price. In some jurisdictions, consumer-facing prices must be inclusive. In other business-to-business settings, quotes are often GST-exclusive, with tax added later. Failing to identify the mode can lead to underbilling or margin erosion.
Registered businesses generally need to display the GST rate and GST amount separately on invoices. This creates a defensible compliance record and allows customers with business entitlements to claim tax credits where local law permits.
Choose whether your amount is tax-exclusive (GST needs to be added) or tax-inclusive (GST is already baked in), enter the amount, and enter the GST rate as a percentage.
In exclusive mode, the calculator multiplies your amount by (1 + rate) for the total. In inclusive mode, it divides your amount by (1 + rate) to recover the pre-tax figure, then shows the difference as the GST component.
A business quotes $100 before tax, with a 10% GST rate, in exclusive mode.
GST amount: $100 × 10% = $10. Total amount: $100 + $10 = $110, the figure the customer actually pays.
If instead that $110 were the tax-inclusive sticker price, the calculator would work backward: pre-tax amount = $110 ÷ 1.10 = $100, and GST = $110 − $100 = $10, the same $10 GST component, just isolated from the other direction.
The most common GST error is applying the rate to a figure that already includes it. Adding 10% to a tax-inclusive $110 gives $121, which overstates the tax by $1 and the price by $11. The reverse of adding a percentage is not subtracting that percentage; it is dividing by one plus the rate. Removing 10% GST from $110 means dividing by 1.10, not subtracting $11.
That asymmetry grows with the rate. At 20%, subtracting instead of dividing understates the pre-tax amount by 4% of the total, which on an invoice run of any size is a real reconciliation problem.
Rounding is the second trap. Rounding GST on every line and rounding the invoice total independently produce different answers, and tax authorities generally specify which one governs. Pick one rule, usually rounding the tax on the invoice total, and apply it everywhere so your ledger reconciles against what you actually filed.
This tool applies one rate you supply to one amount. It does not know your jurisdiction, and it makes no attempt to decide which rate applies to what you are selling. That decision is where most of the real difficulty in GST sits.
Rates and structures differ substantially between countries that use the name. Australia and New Zealand apply a single broad rate; India splits it into central, state, and integrated components depending on whether the supply crosses a state border; Canada runs GST alongside provincial taxes that are sometimes harmonised into a single HST and sometimes not. A calculation that is correct in one of those is wrong in another.
Within any of them, zero-rated and exempt supplies are treated differently even though both mean no GST is charged. Zero-rated supplies generally still let you reclaim the GST on your inputs; exempt supplies generally do not. Basic food, healthcare, financial services, exports, and residential rent commonly fall into one category or the other, and the boundaries move.
Registration thresholds, filing frequency, and the point at which a liability arises are also local rules with real consequences. Use this calculator for the arithmetic on an amount, and check the applicable rate and treatment against your own tax authority's current guidance before you invoice or file.
To put GST on an invoice with multiple line items and more than one tax, use the invoice generator, which downloads the finished invoice as a PDF. To work backward from a target take-home margin after tax, use the profit margin calculator.
Inclusive pricing
A pricing model where tax is already embedded in the listed amount.
Tax credit
A reclaim or offset mechanism for eligible input taxes in business systems.
Gross amount
The final amount after GST or VAT has been applied.
Formula
Exclusive: total = amount x (1 + rate); Inclusive: pre-tax = total / (1 + rate)The calculator can add GST to a pre-tax amount or extract GST from a tax-inclusive total.
Step by step
Example
$100 before GST at 10% becomes $110 total with $10 GST.
Related guides
Guide
Add or extract GST and sales tax, distinguish inclusive and exclusive pricing, and verify registration, taxability, location, invoices, returns, and records.
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Last updated . This is the date the calculator or its guidance last changed, taken from our revision history rather than from the last time the site was deployed.