GST calculator
A net price of 100 at a 10% GST rate carries 10 of GST and a gross price of 110. Enter the net amount and the rate that applies, whether 10, 15 or 18 percent, and get both invoice lines at once. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Net price
- 100
- Gst rate
- 10
- Rate percent
- 10
- Rate decimal
- 0.1
- Gst amount
- 10
- Gross price
- 110
Goods and Services Tax, almost always shortened to GST, is the consumption tax printed on invoices in Australia, India, New Zealand, Singapore, Malaysia, and several Canadian provinces. Bookkeepers, checkout pages, and classroom worksheets start from a net GST-exclusive price and a GST rate written as a percentage, then need two results: the GST amount on the tax line and the gross GST-inclusive price the customer actually pays. This GST calculator accepts a non-negative net price and a GST percentage, multiplies the net by the rate over one hundred to obtain the GST amount, and adds that amount to the net to obtain the gross price. Zero percent is allowed and yields a gross price equal to the net.
What GST amount and gross price mean on a tax invoice
Goods and Services Tax is a value-added consumption tax charged on most taxable supplies. A typical tax invoice or checkout line starts from a net price that does not yet include GST, applies a published GST percentage, and prints two extra figures: the GST amount on its own tax line, and the gross price that the buyer pays.
The arithmetic is the same in every GST jurisdiction even when the statutory rate differs: GST amount equals net price times GST rate divided by one hundred, and gross price equals net price plus GST amount. Australia’s standard rate is ten percent, so a one-hundred-dollar net supply produces ten dollars of GST and a one-hundred-ten-dollar gross. India’s common standard rate is eighteen percent; New Zealand’s is fifteen; Singapore’s is nine; Canada’s federal GST is five.
This calculator does not look up a rate from a postcode, GSTIN, or HST overlay: you supply the percentage that applies to the line. Zero percent is a valid rate for GST-free or zero-rated supplies and yields a GST amount of zero and a gross price equal to the net.
What you can do with it
Business-math homework on GST invoices
Students add GST to practice net prices and compare handwritten tax and gross against a deterministic percentage result before submitting.
FAQ
How do I add GST to a net (exclusive) price?
Example: a net of 100 at 10% GST → GST 10, gross 110.
What happens if the GST rate is negative?
A negative GST rate is not allowed; zero percent is valid and yields zero GST and a gross equal to the net.
Does this look up Australia, India, or New Zealand GST rates for me?
No. You supply the percentage that applies to the line (for example 10, 18, 15, 9, or 5). The calculator only applies the arithmetic for a known percent.
Is the GST calculator free?
The browser tool is free and runs locally.
How do I handle an exempt or zero-rated item?
Enter a rate of 0. The GST amount comes out as zero and the gross price equals the net price, which is exactly what an exempt or zero-rated line on an invoice should show.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/fin/gst \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"net_price":100,"gst_rate":10}'const res = await fetch("https://api.kit.forhosting.com/fin/gst", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"net_price": 100,
"gst_rate": 10
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/fin/gst",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"net_price": 100,
"gst_rate": 10
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/fin/gst", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"net_price":100,"gst_rate":10}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"net_price":100,"gst_rate":10}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/fin/gst", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"net_price": 100,
"gst_rate": 10
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "fin.gst",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Limits
max_abs | 1000000000000 |
max_gst_rate_percent | 1000 |
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
A negative GST rate is rejected with invalid_input instead of inventing a rebate.
What GST amount and gross price mean on a tax invoice
A negative GST rate is not a legal or accounting input in this model; it would turn tax into a subsidy, so the task fails with invalid_input rather than returning a negative GST amount that would confuse invoicing software.
Input contract, response shape, and error behaviour
The GST rate must be non-negative; negative values are rejected. Prefer numbers over currency-formatted strings; string numbers are accepted only when they match a strict finite numeric pattern without dollar signs, rupee marks, or thousands separators. Send a JSON body with two required finite numbers: net_price (aliases net, price, amount, exclusive), the non-negative GST-exclusive amount, and gst_rate (aliases rate, percent, gst_percent, tax_rate), the GST rate as a percentage such as ten for ten percent. Absolute values for net_price must stay within one trillion and gst_rate must stay within one thousand percent so intermediate products remain finite in IEEE double precision on the Worker and in the browser. On success the response echoes net_price rounded to cents, gst_rate and rate_percent as the same percentage, rate_decimal as rate over one hundred, gst_amount as the rounded tax, gross_price as net plus GST, and formula as the documented identity. Failed validation—missing fields, non-finite numbers, values outside absolute limits, a negative net price, a negative GST rate, or a non-finite computed GST amount or gross—returns invalid_input and is never charged. Pricing is a flat $0.002 per successful request with unit item. Pair a classic ten percent case with an eighteen percent India-style case and a deliberately negative gst_rate to cover the hard invalid_input path in your own tests.
Where a GST calculator earns its keep
Invoice and estimate tools used by independent contractors can fill a GST line and a due-now gross in one call, then layer a known CGST and SGST split themselves if an Indian intra-state supply requires it. Consumer-math classrooms and exam-prep generators need a deterministic oracle that marks a negative GST rate as invalid instead of silently flipping the sign. Prefer this capability when you already know the exclusive amount and the GST percent and only need the tax amount plus the inclusive total. Storefronts that sell in GST countries and quote exclusive prices can send the cart net and the applicable percent, then display gst_amount and gross_price without reimplementing percentage math in every client. Quality-assurance suites for billing libraries can pin one hundred at ten percent to GST ten and gross one hundred ten, plus a fractional net such as forty-nine point ninety-nine for cent-rounding checks, and a deliberately negative rate to prove the hard invalid_input path. This landing targets people searching for a GST calculator, GST amount from net price, or gross price with GST added; it is not a VAT inclusive-to-exclusive converter, not a United States sales-tax ZIP lookup, and not an India GSTIN check-digit tool. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when developers deliberately send a negative rate. Round-trip checks are easy: recompute net times rate over one hundred by hand, confirm it equals the published gst_amount within the same two-decimal rounding, then confirm that net plus gst_amount equals the published gross_price at the published $0.002 automation rate.
Integration use cases
GST-exclusive checkout and tax invoices
Storefronts and invoice tools send a net exclusive price and the GST percent, then display gst_amount and the GST-inclusive gross without embedding rate tables in every client.
Unit tests for GST billing code
QA and engineering pin known-good cases such as one hundred at ten percent to GST ten and gross one hundred ten, plus deliberate negative-rate rejections.
Technical questions
Should I enter 10 or 0.10 for a 10% GST rate?
Enter 10. The gst_rate field is a percentage (10 means 10%). The response also includes rate_decimal (0.10) for convenience.