GST Calculator
Add GST to a base price, or work backward from a GST-inclusive price to find the original amount and tax — with the CGST/SGST or IGST split.
This tool calculates GST arithmetic only and does not determine which rate applies to a specific product or service. See our Disclaimer.
Last reviewed: — rate structure checked against the GST 2.0 reform of 22 September 2025.
The formula
Adding GST: GST amount = (base price × GST rate) ÷ 100, and the total is base price + GST amount.
Removing GST from a price that already includes it: base price = inclusive amount ÷ (1 + rate/100). It's not as simple as subtracting the percentage directly, because the rate applies to the base, not the inclusive total.
For a supply within the same state, the GST amount splits evenly into CGST (central) and SGST (state). For a supply across states, the full amount is charged as IGST instead, with no split.
Worked examples
Adding 18% GST to 1,000 within the same state gives a GST amount of 180 (CGST 90 + SGST 90), for a total of 1,180.
Removing 18% GST from an inclusive price of 1,180 gives a base price of exactly 1,000 — confirming the two directions are consistent.
Current GST rate slabs (India)
Under the GST 2.0 reform effective 22 September 2025, the previous 5%/12%/18%/28% structure was simplified to mainly two slabs — 5% for everyday essentials and 18% as the standard rate for most goods and services — with a new 40% slab for select luxury and "sin" goods (tobacco, pan masala, large vehicles, betting/gaming, and similar). A 0% (Nil) rate applies to a wide list of essentials, and special rates of 0.25%–3% remain for precious metals and diamonds.
This calculator doesn't look up which rate applies to a specific product — check the current rate for your specific item on the official GST portal (gst.gov.in) or with a tax professional, since exact classifications can be nuanced and are subject to change.
Method and sources
Adding GST multiplies the pre-tax amount by the rate; removing it divides the GST-inclusive amount by (1 + rate ÷ 100). Within one state the tax is split equally into CGST and SGST; on a supply between states the full rate is charged as IGST. The slab structure above comes from the GST Council's 56th meeting (3 September 2025), put into effect through the CBIC rate notifications issued on 17 September 2025.
Limitations
This is an arithmetic calculator, not a compliance or filing tool. It doesn't account for the Composition Scheme, reverse charge mechanism, input tax credit, or item-specific HSN classification. For actual GST filing or a specific transaction, verify the applicable rate and rules with a chartered accountant or the official GST portal.
Frequently asked questions
Why can't I just subtract 18% from an inclusive price?
Because 18% GST was added to the base price, not the inclusive total. Subtracting 18% of the inclusive amount would overcorrect — you need to divide by (1 + rate/100) instead.
When do I use CGST + SGST vs IGST?
CGST and SGST apply when the supplier and the place of supply are in the same state — the tax splits evenly between the central and state governments. IGST applies when the supply crosses state lines, charged as a single combined rate.
Does this calculator tell me the GST rate for my product?
No — it only does the arithmetic once you know the rate. Which rate applies to a specific product or service depends on its HSN/SAC classification, which can change over time (most recently with the GST 2.0 reform in September 2025). Check the current rate on the official GST portal or with a tax professional.