Reverse GST Calculator: Remove GST from a Total

Remove GST from a GST-inclusive total and recover the original price. Enter the total and GST rate to see the base price and GST amount instantly.

GST-inclusive total

Enter the GST-inclusive total in the currency shown on the source receipt, price, quote, or invoice.

GST Rate (%)

These figures are an example. Replace them with your GST-inclusive total.

Base Amount100.00

GST (15%)+ 15.00

Entered totalGST-inclusive total

115.00

How this split is calculated

How this GST-inclusive total splits

Divisor: 1 + 15 / 100 = 1.15

At 15%, GST is 13.04% of this GST-inclusive total.

Directly subtracting 15% would give 97.75 as the base amount (incorrect).

That is 2.25 away from the correct base amount.

GST-inclusive total breakdown

The segments show each part's share of the total. The GST share is not the same as the entered GST rate.

Pre-GST amount (86.96% of total): 100.00
GST at 15% (13.04% of total): 15.00

GST was added to the base amount, so divide the inclusive total by the divisor instead of subtracting the rate directly.

Amounts use the currency on the source receipt, price, quote, or invoice. This calculator does not convert currencies.

This result handles one GST rate at a time; split mixed-rate amounts before calculating.

Values display to two decimal places. Invoice and filing rounding rules can differ by jurisdiction.

What this result means for you

For a $115.00 total at 15% GST, the base price is $100.00 and the GST amount is $15.00. The calculator divided the total by 1.1500, then subtracted the base from the total.

Subtracting 15% directly would give $97.75, which is $2.25 away from the correct base. GST was added to the base price, so reverse it with division, not subtraction.

Use the GST rate that applied to the original transaction. This calculator separates the amounts; it does not decide which rate or tax treatment applies.

Includes the total, GST rate, base price, GST amount and formula used. The calculation stays in your browser.

Remove GST from a Total

Divide the GST-inclusive total by 1 plus the GST rate as a decimal. A $115 GST-inclusive total at 15% becomes a $100 base price and $15 GST. Do not subtract 15% from $115: that gives $97.75, not the original price.

Reverse GST formula

Base price = Total price / (1 + GST rate / 100)GST component = Total price - Base price

Need to add GST, use Excel, or a country-specific method?

This page only recovers the base price and GST from an inclusive total. Open the matching page when the job is different.

Add GST to a pre-tax price GST formulas in Excel New Zealand GST at 15%Australia GST at 10%Canada GST/HST split

How to Use the Reverse GST Calculator

Enter the GST-inclusive total

Enter the final amount that already includes GST.

Enter the GST rate

Use the GST rate that applied to the original transaction.

Check the base price and GST

Review the recovered base price and the GST amount inside the total.

Reverse GST and Remove GST Mean the Same Task

Both phrases describe working backwards from a total that already includes GST. The result has two parts: the original price before GST and the GST amount inside the total. Enter the inclusive total—not the pre-tax price—to use this calculator.

Reverse GST Formula

First calculate Base price = Total price / (1 + GST rate / 100). Then calculate GST amount = Total price - Base price. For 15%, divide by 1.15; for 10%, divide by 1.10. The divisor changes with the rate, but the formula stays the same.

Worked example: remove 15% GST from $115

A $115 GST-inclusive total at 15% becomes a $100 base price and $15 GST. Divide $115 by 1.15 to get $100, then subtract $100 from $115 to get the $15 GST amount. At 10%, a $220 total becomes $200 before GST and $20 GST because $220 / 1.10 = $200.

Common mistakes when removing GST

Do not subtract the GST percentage from the total: the percentage was calculated from the smaller base price. Do not treat the total as the base or apply one rate across items that used different GST rates. Reverse each amount with the rate that actually applied, then check rounding against the source invoice.

When to Use a Reverse GST Calculator

Use it when you know a GST-inclusive sale, receipt, invoice or payment total and need the price before GST plus the GST amount. If you already know the pre-tax price and want the final total, add GST on the home-page calculator.

Use the GST Rate That Applied to the Total

The formula accepts any GST percentage, but the correct rate depends on the original transaction. Confirm the rate on the invoice or with the relevant tax authority. If one total contains items taxed at different rates, calculate those lines separately instead of applying one rate to the whole total.

Reverse GST Calculator FAQ

Q1.How do I remove GST from a total?

Divide the GST-inclusive total by 1 plus the GST rate as a decimal. The result is the price before GST. Subtract that base price from the total to get the GST amount.

Q2.What is the reverse GST formula?

Base price = Total price / (1 + GST rate / 100). GST amount = Total price - Base price. For example, $115 / 1.15 = $100 before GST, leaving $15 GST.

Q3.Why is subtracting the GST rate from the total wrong?

GST is a percentage of the base price, not the final total. Subtracting 15% from $115 gives $97.75, but the original base was $100. Division reverses the percentage increase correctly.

Q4.Can I use any GST rate?

Yes. Enter the GST percentage that applied to the transaction. Confirm the rate first, and calculate mixed-rate items separately rather than applying one rate to the whole total.

Q5.What is the difference between reverse, inclusive and exclusive GST calculations?

Reverse GST works backwards from a known GST-inclusive total. To add GST to a pre-tax price, use the home-page calculator. Excel formulas, New Zealand 15%, Australia 10%, and Canada GST/HST splits each have their own page.

Q6.Can I use this result for a GST return or invoice?

Use it to check the mathematical split between the base price and GST amount. Confirm the applicable rate, rounding, invoice rules and reporting treatment with the relevant tax authority or adviser before filing.

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