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GST Calculator
Add or remove GST, with CGST, SGST and IGST split and Indian number formatting.
- Available — Live on this site right now.
- Browser Tool — Runs in the browser you are reading this in.
- No Install — Nothing to download, no extension, no account.
- Client-Side — Runs entirely on your device. No test data is uploaded.
This page explains the tool. The tool itself is one click away and needs no sign-in.
Open GST CalculatorWhat this calculator does
The GST Calculator works in three modes. ADD GST takes an exclusive price and adds the tax. REMOVE GST takes a GST-inclusive amount and works backwards to the base price. BREAKDOWN shows the full component split.
The tax split follows the Indian structure: an intra-state supply splits the total rate evenly into CGST and SGST, while an inter-state supply puts the whole rate into IGST. The rate buttons cover 0%, 5%, 12%, 18% and 28%, and a custom rate is accepted.
Two extra sections handle the cases that cause the most argument in practice: a discount-plus-GST calculator that lets you choose whether the discount or the tax is applied first, and a side-by-side comparison of two GST rates on the same amount. Amounts are formatted in the Indian numbering system.
How to use it
- Decide whether your amount already includes GSTThis is the whole decision. If the figure on the invoice is what the customer pays, use REMOVE GST. If it is the pre-tax price, use ADD GST. Getting this backwards is the single most common GST error.
- Enter the amount and choose the rateUse one of the standard rate buttons or type a custom rate. Decimal amounts and decimal rates are both accepted.
- Choose intra-state or inter-stateINTRA-STATE (CGST + SGST) splits the rate in half between the two; INTER-STATE (IGST) applies the whole rate as IGST. The total tax is identical either way — only the split differs.
- Press CALCULATE GSTYou get the base amount, the GST amount, the final amount and the component split. COPY RESULT and COPY FORMULA copy the answer or the working, and ★ SAVE CALCULATION keeps it in your browser.
- Use the discount section when both applyChoose whether the discount comes first or the GST does. The two orders give different final amounts, which is exactly why the option exists — the page's own FAQ asks whether GST should be calculated before or after a discount.
What the results mean
Base amount
The taxable value before GST. In ADD mode it is what you entered; in REMOVE mode it is the figure the calculator derived by dividing the inclusive amount by the tax factor.
GST amount
The tax itself. In ADD mode it is base × rate ÷ 100; in REMOVE mode it is the inclusive amount minus the derived base, which is the only way to get it right without rounding drift.
CGST and SGST
On an intra-state supply the rate is split evenly — 18% GST is 9% CGST plus 9% SGST — with the central and state halves shown separately because they are reported separately.
IGST
On an inter-state supply the entire rate is IGST: 18% GST is 18% IGST, with no CGST or SGST component. The total tax is the same as the intra-state case.
Why removing 18% means dividing by 1.18
Because the tax was added to the base, not to the total. If base × 1.18 = inclusive, then base = inclusive ÷ 1.18. Subtracting 18% of the inclusive amount instead gives a base that is too low — and the page has a FAQ on precisely this point.
The formula
These are the expressions the calculator evaluates, written out so you can reproduce any result by hand.
Worked example
₹10,000 at 18% GST, worked in both directions and split both ways.
- ADD — base
- ₹10,000
- ADD — GST at 18%
- 10,000 × 18 ÷ 100 = ₹1,800
- ADD — final
- ₹11,800
- Intra-state split
- CGST 9% = ₹900, SGST 9% = ₹900
- Inter-state
- IGST 18% = ₹1,800
- REMOVE from ₹11,800
- 11,800 ÷ 1.18 = ₹10,000, GST = ₹1,800
Adding and removing are exact inverses: ₹10,000 becomes ₹11,800, and ₹11,800 comes back to ₹10,000. Subtracting 18% of ₹11,800 instead would give ₹9,676 — wrong by ₹324, which is the mistake dividing by 1.18 avoids.
Limits worth knowing
A browser can only report what the platform gives it. These are the honest boundaries of this page, so a result is never read as more than it is.
- It computes the arithmetic; it does not know your rates. Which HSN or SAC code applies, which rate that code carries, and whether a supply is intra-state or inter-state are determinations you make and enter — the calculator does not look them up and has no rate database.
- It is not tax advice or a compliance tool. There is no input-tax-credit handling, no reverse charge, no cess, no TDS or TCS, no e-invoicing and no return filing. For anything you will actually file, confirm with a qualified professional or the GST portal.
- Rounding on a real invoice follows the supplier's own rules and the applicable regulations. The calculator shows unrounded arithmetic, so a paise-level difference against an invoice line is normal.
- Nothing is uploaded. Amounts, saved calculations and settings stay in your browser's local storage, which is what the page's own privacy FAQ says.
Tips
- Say out loud which number you have before choosing a mode: “this is what the customer pays” means REMOVE, “this is my price before tax” means ADD.
- When a discount and GST both apply, settle the order first — discount-then-GST and GST-then-discount give different totals, and the invoice has to match the contract.
- Use the two-rate comparison when a classification is genuinely ambiguous between, say, 12% and 18%. Seeing both totals side by side is more useful than recalculating twice.
Troubleshooting
Removing GST gives a different answer than I expected.
You are probably subtracting the rate from the inclusive amount. Removing 18% means dividing by 1.18, not multiplying by 0.82. The calculator does it correctly; the discrepancy is the manual method.
Which should I pick, CGST + SGST or IGST?
Intra-state supplies — supplier and place of supply in the same state — use CGST + SGST. Inter-state supplies use IGST. The total tax is identical; only the split and the reporting change.
My total is a rupee off from the invoice.
Almost always rounding. Invoices round per line and sometimes per component, while the calculator shows the raw arithmetic. Compare the base amount rather than the total to see whether the underlying figures agree.
Should the discount come before or after GST?
Commercially it depends on your terms, and it changes the total. Use the discount section's order control to model whichever your contract or invoice specifies rather than assuming.
Ready to run it?
Add or remove GST, with CGST, SGST and IGST split and Indian number formatting. Nothing to install, and it opens in this browser.