Reverse GST Calculator

Work backwards from a final, GST-inclusive amount to the price before tax. If you know both the pre-tax and final price, it can also tell you which GST rate was applied — useful for checking supplier bills.

Rates and rules last reviewed: 30 September 2026

Price before GST

₹10,000.00

GST included @ 18%: ₹1,800.00
CGST @ 9%: ₹900.00
SGST/UTGST @ 9%: ₹900.00
Final price (incl. GST): ₹11,800.00

For guidance only

This calculator gives an estimate for general information. It is not tax or legal advice. Check the applicable rate and rules for your case on the official sources below or with a qualified professional.

How to use the Reverse GST Calculator

Choose what you know: the final price and rate, or the price before and after GST.
Enter the amounts (and the rate, if known).
Read the pre-tax price and GST — or the rate that was charged.

Formula

Price before GST = Final price × 100 ÷ (100 + Rate)

GST = Final price − Price before GST

GST rate % = (Final price − Price before GST) ÷ Price before GST × 100

Why reverse GST needs a different formula

A GST-inclusive price is (100 + rate)% of the original price. So to get back to 100%, divide by (100 + rate) and multiply by 100. A common mistake is to subtract the rate percentage of the total, which removes too much tax.

₹11,800 at 18%: correct vs common mistake
Method	Price before GST	GST
Correct: 11,800 × 100 ÷ 118	₹10,000	₹1,800
Wrong: 11,800 − 18% of 11,800	₹9,676	₹2,124

Finding the rate that was charged

If a bill shows a price before and after tax but not the rate, the rate is (after − before) ÷ before × 100. If the answer isn't a standard slab, the bill may include rounding, cess, discounts or other charges.

Worked examples

Final price ₹590 including 18% GST

Price before GST = 590 × 100 ÷ 118 = ₹500
GST = 590 − 500 = ₹90

₹500 + ₹90 GST

Which rate turns ₹2,000 into ₹2,100?

Difference = 2,100 − 2,000 = ₹100
Rate = 100 ÷ 2,000 × 100 = 5%

GST rate: 5%

Important notes

Results are rounded to the nearest paisa. If a bill was rounded to the nearest rupee, the derived rate may be slightly off a standard slab.

Frequently asked questions

What is the reverse GST formula?

Price before GST = GST-inclusive price × 100 ÷ (100 + GST rate). For 18%, divide the inclusive price by 1.18.

Is 'reverse GST' the same as reverse charge (RCM)?

No. This page is about back-calculating GST from an inclusive amount. The reverse charge mechanism is a different concept in which the recipient, instead of the supplier, pays GST to the government.

How do I find GST from an MRP?

MRP includes all taxes. Divide the MRP by (1 + rate ÷ 100) to get the taxable value; the difference is the GST.

Sources and review

Last reviewed on 30 September 2026 by the BizToolsIndia editorial team. Official references:

Spotted an error or a rate change? Tell us.