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Free GST calculator — add or remove GST

Short answer

To add GST, multiply the price by the rate: ₹1,000 at 18% is ₹180 GST, ₹1,180 total. To remove GST from an inclusive price, divide by (1 + rate): ₹1,180 ÷ 1.18 = ₹1,000. The calculator below does both at any rate and splits the tax into CGST + SGST or IGST, in your browser, with no signup.

  • No account, no email
  • Offline after first load
  • No data sent anywhere
  • Paisa-exact rounding
The amount is…
GST rate

12% and 28% are for invoices dated before 22 September 2025.

Buyer is in…

GST on ₹1,000 at every rate

Worked examples, both directions. "Add" treats ₹1,000 as the price before GST; "remove" treats ₹1,000 as the price already including GST.

Rate Add: GST Add: total Remove: price before GST Remove: GST inside
0.25% ₹2.50 ₹1,002.50 ₹997.51 ₹2.49
3% ₹30.00 ₹1,030.00 ₹970.87 ₹29.13
5% ₹50.00 ₹1,050.00 ₹952.38 ₹47.62
12% ₹120.00 ₹1,120.00 ₹892.86 ₹107.14
18% ₹180.00 ₹1,180.00 ₹847.46 ₹152.54
28% ₹280.00 ₹1,280.00 ₹781.25 ₹218.75
40% ₹400.00 ₹1,400.00 ₹714.29 ₹285.71

The two formulas

  • Add GST: GST = price × rate ÷ 100; total = price + GST.
  • Remove GST: price before GST = inclusive price × 100 ÷ (100 + rate); GST = inclusive price − price before GST.
  • Split: same state → CGST and SGST (or UTGST) at half the rate each; different state → IGST at the full rate.

A common mistake: taking 18% off an inclusive price. 18% of ₹1,180 is ₹212.40, not the ₹180 of GST it actually contains.

Who this calculator is for — and who should skip it

Use it if…

  • You are writing a quote and need the GST-inclusive price a customer will pay.
  • A supplier quoted "₹X including GST" and you want the price before tax and the input credit in it.
  • You need to know how a figure splits into CGST + SGST versus IGST before raising an invoice.
  • You are a CA, student or freelancer checking an invoice's arithmetic.

Skip it if…

  • You need to know which rate applies to your item — that comes from its HSN or SAC code in the CBIC rate notifications, not a calculator.
  • You need a printable tax invoice — use our free GST invoice generator, which does this same split per line.
  • You bill every day and file GSTR-1 from those bills. That is billing software, and ours is ₹399 a month per app with unlimited users.

Put this calculator on your own site

This page is free to link to, quote and recommend — in a blog post, a forum answer, a WhatsApp group or a client handout. No permission needed and no attribution required: https://399apps.com/tools/gst-calculator/

FAQ

Questions people ask about calculating GST

I have a price that already includes 18% GST — how do I find the price before GST? +
Divide the GST-inclusive price by 1.18. For ₹1,180 that gives ₹1,000 before GST and ₹180 of GST. In general the price before GST is the inclusive price × 100 ÷ (100 + rate). Choose "Remove GST" in the calculator above and it does this for any rate, rounded to the paisa so the two parts add back to exactly what you typed.
How much GST do I add on ₹1,000 at 18%, and how is it split between CGST and SGST? +
18% of ₹1,000 is ₹180, so the total is ₹1,180. If the buyer is in your own state, that ₹180 is charged as ₹90 CGST plus ₹90 SGST (or UTGST in a union territory). If the buyer is in another state, the whole ₹180 is charged as IGST. The rate is the same either way; only the split changes.
Do I charge CGST + SGST or IGST — how do I decide? +
Compare your state with the place of supply. For goods, the place of supply is usually where the goods are delivered; for most services, it is where the buyer is registered or located. Same state as yours: CGST + SGST, half the rate each. Different state: IGST at the full rate. Exports and supplies to SEZ units are treated as inter-state.
Which GST rates should I use now — are 12% and 28% still valid? +
From 22 September 2025, most goods and services moved to two main rates, 5% and 18%, with 40% for a short list of luxury and sin goods. 3% (gold, silver, jewellery) and 0.25% (rough diamonds and precious stones) carry on. 12% and 28% are kept in the calculator for invoices dated before that change. Always confirm your item's current rate against its HSN or SAC code on the CBIC rate notifications.
Is anything I type into this GST calculator sent to a server or saved? +
No. The calculator runs entirely in your browser. It sends nothing you type anywhere and stores nothing — no account, no cookie for the amounts, no log. Close the tab and the numbers are gone.
I run a small shop and work out GST on a calculator for every bill — when is it worth moving to billing software? +
A calculator is fine for a quote or a one-off check. Once you are writing several GST bills a day, the risk is copying a figure wrong and having GSTR-1 not match your books. Billing software applies the HSN rate per item, picks CGST/SGST or IGST from the customer's state, and builds GSTR-1 from the same invoices, so there is nothing to copy.
When the calculator is open all day

Billing software that does the GST maths on every bill

399Apps applies the right rate per item, splits CGST/SGST or IGST from the customer's state, and builds GSTR-1 from the same invoices — flat ₹399 per month per app, unlimited users, cloud or self-hosted.

See pricing Create a free GST invoice