GST & Tax
Reverse GST Calculator
Work back from a GST-inclusive price or MRP to the price before GST and the tax inside it.
Rates last verified 2025-09-22 — always confirm against the current notification before filing.
How reverse GST works
A reverse GST calculation starts from a price that already includes GST, such as an MRP, a restaurant bill or a vendor's all-in quote, and splits it into the taxable value and the tax inside it. Divide the inclusive price by (1 + rate/100) to get the price before GST, and the rest is GST. Put another way, the GST inside an inclusive price is rate ÷ (100 + rate) of it.
The common mistake is to take the GST rate straight off the inclusive price. 18% of ₹1,180 is ₹212.40, but the GST inside ₹1,180 is only ₹180, because the 18% was charged on ₹1,000, not on ₹1,180. At 18%, the GST inside any inclusive price is 15.25% of it; at 5%, it's 4.76%; at 40%, it's 28.57%; and at the 3% rate for gold and jewellery, it's 2.91%.
To go the other way and add GST to a price, use the GST Calculator. If you don't know which rate applies, look up the item in the HSN/SAC Finder.
Worked examples
A packaged product at 5%, with an MRP of ₹525. ₹525 ÷ 1.05 = ₹500 is the price before GST, and the GST is ₹25. Sold within the state, that's ₹12.50 CGST and ₹12.50 SGST.
A restaurant bill of ₹1,050. Most restaurants charge 5% GST, so the food costs ₹1,000 and the GST is ₹50: ₹25 CGST and ₹25 SGST.
A ₹2,360 all-in quote from a service provider at 18%. ₹2,360 ÷ 1.18 = ₹2,000 for the service and ₹360 GST. If the provider is in another state, the whole ₹360 is IGST.
Frequently asked questions
What is the reverse GST formula?
Price before GST = inclusive price ÷ (1 + rate/100), and GST = inclusive price − price before GST. For ₹1,180 at 18%: ₹1,180 ÷ 1.18 = ₹1,000, so the GST is ₹180. You can also find the GST directly as inclusive price × rate ÷ (100 + rate).
Does MRP include GST?
Yes. MRP printed on packaged goods is the maximum retail price inclusive of all taxes, so a retailer can't charge GST on top of it. To find the GST inside an MRP, enter the MRP here with the product's GST rate.
Why isn't the GST just 18% of the total?
Because the 18% was charged on the price before GST, not on the total. On a ₹1,180 bill, 18% of ₹1,000 is ₹180. Taking 18% of ₹1,180 gives ₹212.40, which overstates the tax by ₹32.40. The GST inside an 18%-inclusive price is always 15.25% of it.
Which amount goes on the invoice as the taxable value?
The price before GST. A GST invoice shows the taxable value, the CGST and SGST (or IGST) separately, and the total. If you agreed on an all-in price with a customer, work back to the taxable value here, then enter that in the GST Invoice Generator.
Can I claim input tax credit on the GST worked out here?
Only if you're GST-registered, the purchase is for your business, and the supplier has issued a proper tax invoice and reported it so it shows in your GSTR-2B. A retail bill that only shows an inclusive price, with no GSTIN or tax breakup, isn't enough for a claim.