GST Calculator
Add GST to a base price or remove GST from a GST-inclusive total. Enter the amount and rate to see the base, GST and total instantly.
Price already includes GST? Remove GST with the Reverse GST Calculator
Calculating for Singapore? Use the Singapore GST calculator (9% + service charge)
In New Zealand? Use the NZ GST calculator (15%, IRD ×3÷23 method)
In Australia? Use the Australian GST calculator (10%, ÷11 method)
How to Use the GST Calculator
Enter the Amount
Enter the base price before GST or the final total that already includes GST.
Set Rate and Direction
Enter the applicable GST rate, then choose Add GST or Remove GST for your starting amount.
Check the Breakdown
Review the base amount, GST amount and total, then copy the result if needed.
Add or Remove GST in One Calculator
Enter an amount and GST rate, then choose the direction that matches your starting figure. Use Add GST when the amount excludes GST. Use Remove GST when the total already includes GST. The calculator shows the base amount, GST amount and final total immediately.
The GST Calculation Formula
To add GST: GST = Base amount × GST rate / 100, then add the GST to the base. To remove GST: Base amount = GST-inclusive total / (1 + GST rate / 100), then subtract the base from the total to find the GST. For a complete backwards-calculation guide, use the Reverse GST Calculator.
GST Basics: What Is It?
Goods and Services Tax (GST) is charged as a percentage of a base price. A price may be shown before GST or with GST already included. The calculation changes with that direction, so confirm what your starting amount represents before using the result.
Output Tax and Input Tax for Business
As a business owner you act as a tax collector: you charge GST on sales (Output Tax) and claim back GST on business expenses (Input Tax). The difference is what you pay to or receive from the tax office. Using a calculator ensures these numbers are right and prevents headaches at tax time.
Common GST Calculation Mistakes
The most common error is using the wrong direction. If you start with a net/base price and need to add tax, use the GST Exclusive Calculator — built for B2B quotes, purchase orders, and ex-GST invoicing. If you start with a final price that already includes GST and need to split out the tax, use the GST Inclusive Calculator for receipts and expense claims, or the Reverse GST Calculator when working backwards from a quoted total.
Compliance and Record-Keeping
GST rates, registration thresholds, exemptions and invoice rules vary by jurisdiction. Use the rate that applies to your transaction and confirm filing rules with the relevant tax authority. Keep valid tax invoices for business claims; this calculator provides the arithmetic, not filing advice.
GST Calculator FAQ
Q1.How do I add GST to a price?
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.
Q2.How do I remove GST from a 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.
Q3.Why can’t I subtract the GST percentage directly?
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.
Q4.Which GST rate should I enter?
Enter the rate that applies to your transaction. GST rates and exceptions vary by jurisdiction and can change, so confirm the current rate with the relevant tax authority.
Q5.What is the difference between GST exclusive and GST inclusive?
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.
Q6.Can I use a custom GST rate?
Yes. Enter any GST percentage in the rate field. The calculator applies the same add or remove formula to the amount you provide.
Q7.Does this calculator file or pay GST for me?
No. It calculates the base, GST and total amounts only. Filing rules, registration thresholds, exemptions and invoice requirements depend on your jurisdiction.
Q8.Are my amounts stored or sent to a server?
No. The calculation runs in your browser, and this homepage calculator does not store your amounts on a server.
Recommended Tools
Choose the calculator that matches your calculation direction, workflow, or tax task.
GST Exclusive Calculator
Add GST to a price before tax. Enter the GST-exclusive amount and GST rate to calculate the GST amount and final GST-inclusive total for a quote or invoice.
GST Inclusive Calculator
Split a GST-inclusive total into the price before GST and the GST amount. Enter the total and GST rate to break down receipts, prices and expense claims.
Reverse GST Calculator
Use this reverse GST calculator to remove GST from a GST-inclusive total. Get the original price and GST amount with the formula, examples and common mistakes.
Canada GST/HST Calculator (All 13 Provinces)
Calculate Canadian sales tax for all 13 provinces: GST 5%, HST 13-15%, PST and Quebec QST. Add, remove or reverse tax instantly with official CRA rates.
Quebec GST/QST Reverse Calculator
Reverse or add Quebec sales tax instantly: GST 5% + QST 9.975% calculated in parallel per Revenu Québec rules. Split any total into base, GST and QST.
Singapore GST Calculator (9%)
Add or remove Singapore's 9% GST instantly, with an optional 10% service charge for restaurant bills. Official IRAS rates, history table and bill-split tips.
GST Calculator NZ — Add or Remove 15% GST
Add 15% GST to a price or pull the GST out of a GST-inclusive total with Inland Revenue's ×3÷23 method. Free NZ GST calculator with formulas and examples.
GST Calculator Australia — Add or Remove 10% GST
Add 10% GST to a price or pull the GST out of a GST-inclusive total with the official ÷11 method. Free Australian GST calculator with formulas and examples.