GST Calculator: How to Add or Remove GST and Split CGST/SGST Correctly

CodexFuse Team · 2026-10-30T12:45:07.941Z · 9 min read min read

Add GST to a net price or extract it from a gross price, split CGST/SGST correctly, and avoid the one formula mistake that overstates your tax.

A gst calculator answers one deceptively simple question: how much of the price on an invoice is tax, and how much is actually yours? Get that split wrong and you either overcharge a customer, under-report tax, or quietly absorb a cost that was never yours to pay. This guide shows you how to add GST to a net price, extract it from a gross price, and split it correctly between CGST and SGST — with a worked example you can check line by line.

The pain is familiar to anyone who sells across India. A customer sees one price, your books need another, and the tax department wants a third number broken down by component. A free, browser-based GST calculator removes the arithmetic risk — but only if you understand what it is computing.

What is GST and how does the CGST/SGST split work?

GST, or Goods and Services Tax, is India's indirect tax on the supply of goods and services, in force since 1 July 2017. On a sale within one state, the tax is collected as two equal halves: CGST goes to the central government and SGST goes to the state government. On a sale between two states, the same tax is collected as a single integrated tax, IGST, with no split.

That distinction decides which number lands on your invoice. Sell within your state and the invoice shows CGST and SGST side by side, each exactly half the total GST. Sell across a border and it shows one IGST line for the full amount. The total tax is the same either way; only the presentation changes.

How do you add GST to a price?

To add GST to a net price, multiply the net price by the GST rate and add the result to the original price. The formula is: GST amount = net price × (rate ÷ 100), and final price = net price + GST amount. For an intra-state sale, split the GST amount equally into CGST and SGST.

Take a net price of ₹10,000 at 18%. The GST is ₹10,000 × 0.18 = ₹1,800, so the final price is ₹11,800. The split is ₹900 CGST and ₹900 SGST. If the same sale were inter-state, the invoice would show ₹1,800 of IGST instead — same total, different lines.

How do you remove GST from a price?

To remove GST from a GST-inclusive price, divide the gross price by one plus the rate, then subtract the result from the gross price. The formulas are: net price = gross price ÷ (1 + rate ÷ 100), and GST = gross price − net price. Dividing, not subtracting a percentage of the gross price, is the step most people get wrong.

The common mistake is subtracting 18% of ₹11,800, which gives ₹2,124 — too much, because that 18% is being taken on a figure that already includes tax. The correct route: ₹11,800 ÷ 1.18 = ₹10,000 net, so GST is ₹1,800. Whenever a marketplace or customer quotes you an inclusive price, divide first.

A worked example: a Jaipur home-decor seller prices a cushion set

Meet Priya, a fictional seller in Jaipur who makes block-printed cushion cover sets. She sells mostly within Rajasthan, with occasional orders from Delhi. Her costs and pricing are real numbers; only the business is invented. Here is how she prices one set end to end.

Step 1: Set the net price

Priya's material, printing and stitching cost ₹640 per set, and she wants a ₹610 margin. Her net price is therefore ₹1,250. This is the price before tax — the number her own books care about.

Step 2: Add GST for a within-Rajasthan sale

Her product falls under a 12% slab. GST is ₹1,250 × 0.12 = ₹150, so the customer pays ₹1,400. Because buyer and seller are in the same state, the invoice shows ₹75 CGST and ₹75 SGST. She checks this in seconds on the GST calculator: Add GST mode, price ₹1,250, rate 12%.

Step 3: Handle the Delhi order differently

A Delhi customer orders the same set at ₹1,400. The tax is still ₹150, but now it is ₹150 of IGST on a single line — no CGST/SGST split. Priya's total collection is identical; only the invoice lines change.

Step 4: Reverse-check a marketplace price

A marketplace later lists her set at ₹1,400 inclusive. Remove GST mode, ₹1,400 at 12%: ₹1,400 ÷ 1.12 = ₹1,250 net, ₹150 GST. The number matches her costing exactly, so she lists with confidence.

Which GST rate applies to your product or service?

There is no single GST rate: the correct rate depends on your product's HSN code or your service's SAC code. India's slabs were rationalised under GST 2.0 from 22 September 2025, with main rates of 5%, 18% and 40% replacing the older 5%, 12%, 18% and 28% structure. A calculator can do the arithmetic for any rate you type, but it cannot classify your goods for you.

• Check the HSN/SAC first: confirm the classification of exactly what you sell before you pick a rate, because neighbouring categories can sit in different slabs.
• Watch for rate changes: a rate that was right last year may have moved under GST 2.0 — re-check before reissuing a price list.
• Keep the rate on the invoice: the rate, the taxable value and the tax split should all appear, so a customer or auditor can recompute every line.
• Reconcile monthly: compare the GST your invoices show against what your returns report; a single wrong rate, repeated, becomes a noticeable gap fast.

For quick reference, here is what ₹1,000 looks like at the older standard slabs — useful for sanity-checking a result at a glance:

What a GST calculator does not do

Honest limits matter, because a tool that looks authoritative can quietly mislead. The CodexFuse calculator computes the CGST/SGST split for intra-state sales; it does not produce an IGST line for inter-state sales, so for those you take the total GST figure and report it as IGST yourself. Its quick-reference slabs predate the GST 2.0 rationalisation, so treat them as arithmetic examples, not as today's rate card.

It also cannot tell you which rate applies to your product, handle composition-scheme rules, or file a return. Those need your HSN/SAC classification and, for anything beyond straightforward invoicing, a tax professional. Use the calculator for what it is: exact arithmetic on a rate you have verified.

Frequently Asked Questions

What is the formula to add GST?

GST amount = net price × (rate ÷ 100), and final price = net price + GST. At 18% on ₹10,000, that is ₹1,800 of GST and an ₹11,800 total, split ₹900 CGST and ₹900 SGST on an intra-state sale.

What is the formula to remove GST?

Net price = gross price ÷ (1 + rate ÷ 100), and GST = gross price − net price. At 18% on ₹11,800, the net price is ₹10,000 and the GST is ₹1,800.

What is the difference between CGST, SGST and IGST?

CGST goes to the centre and SGST to the state, split equally on intra-state sales. IGST is a single integrated tax on inter-state sales, equal to the full GST amount with no split.

Can I use any GST rate in the calculator?

Yes — you can type any rate from 0% to 100%, with 18% as the default. Just confirm the rate for your goods or services from their HSN/SAC classification before invoicing.

Is the calculator's result enough for filing returns?

The arithmetic is exact, but filing also depends on correct classification, the right scheme, and input tax credit rules. Treat the calculator as a calculation aid and confirm the rate and treatment before you file.

Is the CodexFuse GST calculator free?

Yes — unlimited calculations with no signup, and everything is computed in your browser, so nothing you type leaves your device.

Stop guessing at tax — price with the split in front of you

GST mistakes rarely announce themselves. They hide in a copied spreadsheet, a guessed rate, or a discount approved on the wrong number — and they surface weeks later, when fixing them costs real money. The fix is unglamorous: verify your rate, add or remove the tax with the right formula, and check the CGST/SGST split before the invoice goes out.

Run your next price through the free GST calculator now — add mode for your net price, remove mode to reverse-check any inclusive quote — and make the split part of every invoice. And if the admin around your business is eating more time than the business itself, move your hosting, email, security and backups to CodexFuse: one fully managed platform on pay-as-you-go credits, no subscriptions, no server babysitting. Get started today and put your time back into selling.