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GST Calculator

Calculate GST (Goods & Services Tax) easily: Add GST to base amount or Reverse GST (extract tax from total) at the current 5%, 18% and 40% rates or any custom rate.

Runs in your browser. Nothing you add is uploaded.

What the GST Calculator does

GST calculations go wrong in one specific way: people subtract the GST percentage from a GST-inclusive price. That is arithmetically incorrect, because the percentage was applied to the base amount, not to the total. This calculator handles both directions properly — adding GST to a base price, and extracting GST from an inclusive price — and splits the result into CGST and SGST where that applies.

How to calculate GST

  1. Choose the direction: add GST to an exclusive amount, or remove GST from an inclusive amount.
  2. Enter the amount and select the GST rate — 5%, 18% or 40% since 22 September 2025, or type another rate.
  3. Read the tax amount and the net and gross totals.
  4. For intra-state supply, use the CGST and SGST split, each being half the total rate.

The GST Calculator runs entirely in your browser — nothing you enter is uploaded, stored, or logged.

How it works

GST Added (Exclusive)

GST Amount = (Price × GST%) / 100

Total Amount = Price + GST Amount.

Example: Rs. 1,000 with 18% GST = Rs. 1,000 + Rs. 180 = Rs. 1,180.

Reverse GST (Inclusive)

GST Amount = Price - (Price × (100 / (100 + GST%)))

Calculates the base price and extracted GST from a tax-inclusive total.

Example: Rs. 1,180 with 18% GST -> Base Price = Rs. 1,000, GST = Rs. 180.

When to use it

Issuing a correct invoice

Invoices must show the taxable value and the tax separately. Starting from the price you intend to charge inclusive of tax means working backwards to the taxable value.

Reconciling supplier bills

Checking that the tax charged matches the taxable value at the stated rate catches both supplier errors and incorrect rate classifications.

Pricing to a round retail figure

To land on a clean inclusive price, calculate backwards from the total to find the base price rather than adding tax to a round base.

Good to know

  • To remove 18% GST from an inclusive amount, divide by 1.18 — do not subtract 18%. On ₹1,180 that gives ₹1,000, whereas subtracting gives ₹967.60, which is wrong.
  • Intra-state supply splits the rate equally into CGST and SGST. Inter-state supply uses IGST at the full rate.
  • The rate depends on the HSN or SAC classification of the goods or service, not on the transaction value.
  • Round only the final figure. Rounding intermediate values introduces discrepancies that reconciliation will flag.

Guides that use this tool

Frequently asked questions

What is CGST and SGST?

For intra-state transactions, GST is split equally between Central GST (CGST) and State GST (SGST).

How do I remove GST from an inclusive price?

Divide the inclusive amount by (1 + rate/100). At 18%, an inclusive price of ₹1,180 gives a taxable value of ₹1,180 ÷ 1.18 = ₹1,000, and GST of ₹180. Subtracting 18% from ₹1,180 gives ₹967.60, which is wrong because the 18% was never calculated on ₹1,180 in the first place.

What is the difference between CGST, SGST, and IGST?

For supply within a single state, the total rate is split equally between CGST (central) and SGST (state) — 18% becomes 9% plus 9%. For supply across state lines, the entire rate is charged as IGST. The total tax is identical either way; only the split between authorities differs.

Which GST rate applies to my product?

That is determined by the HSN code for goods or the SAC code for services, as published by the GST Council. Since 22 September 2025 the main slabs are 5% and 18%, with 40% on luxury and sin goods, 3% on gold, and some items zero-rated or exempt. This calculator applies whichever rate you select — it cannot determine the correct classification for you, and misclassification is a compliance matter worth confirming with your accountant.

Is GST calculated on the discounted price?

Yes. A discount shown on the invoice and agreed at or before the time of supply reduces the taxable value, so GST applies to the post-discount amount.

Does this handle reverse charge or input credit?

No. This is a rate calculator for the tax on a single transaction. Reverse charge liability, input tax credit eligibility, and return filing are compliance processes that depend on your registration status and the nature of the supply.

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