A GST calculator adds goods and services tax (GST) to a price or works out how much GST is inside a tax-inclusive total. To add GST, multiply by (1 + rate ÷ 100); to remove it, divide by the same number. For example, 1,000 + 18% GST = 1,180, and a 1,180 inclusive price contains 180 of GST.
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How to use the GST calculator
- Enter the amount.
- Enter the GST rate, for example 18 for 18%.
- Choose “Add GST” if the amount excludes tax, or “Amount includes GST” if it already contains tax.
- Read the total, the price before GST and the GST amount.
GST formulas
| To find | Formula | 18% on 1,000 |
|---|---|---|
| GST to add | amount × rate ÷ 100 | 180 |
| Total with GST | amount × (1 + rate ÷ 100) | 1,180 |
| Price before GST | total ÷ (1 + rate ÷ 100) | 1,180 ÷ 1.18 = 1,000 |
| GST inside a total | total − total ÷ (1 + rate ÷ 100) | 1,180 − 1,000 = 180 |
Use “add GST” when your price excludes tax and “includes GST” when the amount already contains it. A common mistake is to take 18% of a GST-inclusive total: 18% of 1,180 is 212.40, not the 180 actually inside it.
GST calculator worked examples
- India, 18%, exclusive: ₹2,500 + 18% = ₹2,500 + ₹450 = ₹2,950. Within a state this is split into 9% CGST (₹225) and 9% SGST (₹225); between states it is charged as 18% IGST.
- India, 5%, inclusive: ₹1,050 ÷ 1.05 = ₹1,000 before tax, so the GST inside is ₹50.
- Australia, 10%, inclusive: GST is one-eleventh of the price: A$110 ÷ 11 = A$10.
- Canada, 5% GST: C$80 + 5% = C$84. Provinces that use HST charge a single higher combined rate instead.
GST rates by country
| Country | Main GST rates | Notes |
|---|---|---|
| India | 5% and 18%; 40% on selected goods | Two-slab structure from 22 September 2025; some items are exempt (0%) |
| Australia | 10% | Some food, health and education items are GST-free |
| Canada | 5% GST | HST provinces charge one combined GST and provincial rate |
| New Zealand | 15% | Applies to most goods and services |
Rates change, so check the tax authority before you invoice. India’s GST Council removed the old 12% and 28% slabs in 2025; cigarettes and some tobacco products kept their earlier rates for a transition period.
GST-inclusive prices: how much is tax?
For a tax-inclusive price, the GST share of the total is rate ÷ (100 + rate):
| GST rate | Share of the inclusive price | GST in 1,000 inclusive |
|---|---|---|
| 5% | 4.76% | 47.62 |
| 10% | 9.09% | 90.91 |
| 15% | 13.04% | 130.43 |
| 18% | 15.25% | 152.54 |
| 40% | 28.57% | 285.71 |
Rounding and invoices
The GST calculator shows two decimals. Businesses usually calculate GST per invoice line or per invoice according to their accounting system and local rules, so a total built from rounded lines can differ by a few paise or cents. Registered businesses also claim input tax credits for GST they paid on purchases; that netting is outside the gst calculator.
Estimates for education only, not tax, legal or financial advice. Check current rules with the tax authority or a qualified adviser.
CGST, SGST and IGST in India
In India, the total GST rate on a sale is split differently depending on where the buyer is. For a sale within one state, half goes to the central government as CGST and half to the state as SGST. For a sale between states, the whole amount is charged as IGST. The total does not change, only the labels on the invoice.
Take a taxable value of ₹10,000 at 18%. The GST calculator gives ₹1,800 of tax and ₹11,800 in total. For a buyer in the same state the invoice shows CGST ₹900 and SGST ₹900. For a buyer in another state it shows IGST ₹1,800.
Working back from a GST-inclusive price
Shoppers usually see prices that already include tax. To find the tax inside a price, divide by 1 plus the rate. A ₹2,360 price at 18% has a base of ₹2,360 ÷ 1.18 = ₹2,000 and tax of ₹360. In Australia and New Zealand the same idea applies with a 10% and 15% rate; in Australia, the tax inside a GST-inclusive price is simply one eleventh, so a $110 bill holds $10 of GST.
Common mistakes
- Taking 18% of the inclusive price. On ₹2,360 that gives ₹424.80, which is too high.
- Using the wrong rate. Goods and services sit in different slabs, so check the rate for the item before you run the GST calculator.
- Rounding each line item differently from the invoice total. Pick one rule and apply it consistently.
Related converters and calculators
Related tools:
- VAT calculator: UK and EU VAT
- Sales tax calculator: US sales tax
- Discount calculator: price before tax
- Profit margin calculator: pricing
- Percentage calculator: any percent
Sources
PIB (Government of India): Next-generation GST reforms, 2025; CBIC: GST; Australian Taxation Office: GST; Canada Revenue Agency: GST/HST rates.
Questions about this calculator
How do I add 18% GST to a price?
Multiply by 1.18. For example, 2,500 × 1.18 = 2,950.
How do I remove GST from a total?
Divide by (1 + rate ÷ 100). For 18% GST, 1,180 ÷ 1.18 = 1,000, so the GST is 180.
What are the GST rates in India?
From 22 September 2025, the main rates are 5% and 18%, with 40% on selected goods; some items are exempt.
How much GST is in an Australian price?
Australian GST is 10%, so the GST in an inclusive price is one-eleventh of it.
What is the difference between CGST, SGST and IGST?
In India, an intra-state sale splits GST equally into central (CGST) and state (SGST) tax; an inter-state sale is charged as integrated GST (IGST).
Check the assumptions and units before relying on a result. Financial, tax and health estimates do not replace advice for your individual circumstances.
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