Free GST Calculator — Calculate GST Instantly, No Signup

India’s GST system is essential to understand — whether you’re raising an invoice, verifying a bill, or figuring out how much tax you’re actually paying on a purchase. The math is straightforward, but doing it quickly and accurately on a phone or laptop shouldn’t require a spreadsheet.

Today we’re launching GST Calculator on Tools.Town — free, instant, and completely client-side.

What it calculates

The GST Calculator handles both directions of the calculation people actually need:

GST-exclusive (add GST to base price): You have a base amount of ₹1,000 and need to know the final invoice total with 18% GST. The calculator gives you: GST amount (₹180), CGST (₹90), SGST (₹90), and total payable (₹1,180).

GST-inclusive (extract GST from MRP): Your bill shows ₹1,180 and you want to know how much of that is tax. Enter ₹1,180 with 18% inclusive, and you get back the original base amount (₹1,000) and the embedded tax (₹180).

Both directions work for all five standard GST slabs — 0%, 5%, 12%, 18%, and 28% — plus a custom rate field for edge cases.

CGST, SGST, and IGST

For intra-state transactions, GST splits equally between Central GST (CGST) and State GST (SGST). For inter-state transactions, the full rate applies as Integrated GST (IGST). The calculator shows the correct breakdown based on the transaction type you select, so you don’t have to remember the rules.

Why client-side matters for tax tools

We deliberately built this as a pure browser tool. Your purchase amounts, invoice values, and business figures never leave your device. There’s no account, no server request, no tracking of what you’re calculating. The numbers stay yours.

This is the same philosophy behind every tool on Tools.Town — the calculation happens in the browser using a Zod-validated logic module, and the result is immediate.

How to use it

1. Enter your amount — base price or MRP, depending on what you have
2. Select the GST rate — tap one of the preset slabs or type a custom rate
3. Choose inclusive or exclusive — is GST already included in your amount, or are you adding it?
4. Choose intra-state or inter-state — for CGST/SGST vs IGST breakdown
5. Read the result — GST amount, breakdown, and total update instantly

No submit button, no loading spinner. The result updates as you type.

Try it

Open GST Calculator →

If you work with Indian taxes regularly, bookmark it. It handles the three questions that come up most often:

• “How much GST am I paying on this MRP?”
• “What’s the final price after adding 18% GST?”
• “What’s the CGST and SGST split for my invoice?”

Learn more: What is GST? CGST, SGST and IGST Explained →