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.
More worked examples
Removing GST: an invoice total of 2,360 with 18% included, within one state, has a base of 2,000.00 and GST of 360.00, split into CGST 180.00 and SGST 180.00. An interstate total of 1,18,000 at 18% has a base of 1,00,000.00 and IGST of 18,000.00. At 5%, a price of 1,000 includes 47.62 of GST on a base of 952.38, with 23.81 each for CGST and SGST.
Adding GST: 50,000 at 3% gives 1,500.00 (CGST 750.00 and SGST 750.00), a total of 51,500.00. A 20,00,000 price at 40% gives IGST of 8,00,000.00 and a total of 28,00,000.00. 1,000 at 12% on an interstate sale gives IGST of 120.00 and a total of 1,120.00.
Rates and rounding
- You type the rate yourself, so any rate works, including 0, 0.25 and 40. A rate of 0 gives a GST amount of 0.00 and a total equal to the base.
- Amounts are shown to two decimals with no thousands separators or currency symbol: 999 at 18% shows 179.82 of GST, 89.91 each for CGST and SGST, and a total of 1178.82.
- In a CGST/SGST split, the label shows half the rate to two decimals while the amounts use the exact half. For a 0.25% rate the label reads 0.13%, but each amount is 1.25 on a 1,000 base.
- The amount must be above zero and the rate cannot be negative. A blank rate shows "Please enter an amount and GST rate."
Guide
- GST Calculations Explained: Inclusive vs Exclusive — Adding and removing GST correctly, the common mistake with inclusive prices, and when the tax splits into CGST and SGST versus IGST.
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.
How do I find the base price from a total with GST?
Choose "Already includes GST" and enter the total. For 2,360 at 18% the base is 2,000.00 and the GST is 360.00. The base is the total divided by 1.18.
Can I use it for VAT or sales tax?
The arithmetic works for any single percentage rate, because you type the rate. The CGST, SGST and IGST labels are specific to India, so ignore them and use the GST amount line.
Why does the CGST label show 0.13% for a 0.25% rate?
The label rounds half the rate to two decimals. The amounts still use the exact half, so on 1,000 the GST is 2.50 and each of CGST and SGST is 1.25.