Reverse percentage calculator to find the original amount before a percentage increase or discount. Remove GST, undo a markup or find the pre-sale price.

What is the Reverse Percentage Calculator?

A Reverse Percentage Calculator works backwards. You know the final amount and the percentage that was applied, and you want the figure you started with. Typical cases are finding the price before 18% GST was added, the original MRP before a 20% discount, or last year's salary when you only know the new pay and the hike.

Many people try to subtract the percentage from the final amount, which gives the wrong answer. The correct method divides the final amount by (1 + change ÷ 100), and that is exactly what this tool does. Enter a positive percentage for an increase and a negative percentage for a discount or reduction. It is useful for shoppers, small traders, accountants and students preparing for aptitude exams.

How to use the Reverse Percentage Calculator

Enter the amount you can see now in Final amount, such as a GST-inclusive bill of 1180.
Enter the percentage that was applied in Applied change (%): 18 for an 18% increase, or -20 for a 20% discount.
Press Calculate to get the original amount before the change.
Copy the result for your invoice, accounts or homework.
Press Reset to work out another original value.

Features

Recovers the starting value from a final amount and applied %
Handles both increases (positive %) and reductions (negative %)
Accepts changes from just above -100% up to 10,000%
Inline validation for empty or invalid entries
Copy result in one tap, on any screen size

Why use this reverse percentage calculator

Remove GST or tax from an inclusive price correctly
Check whether a 'discounted' price really matches the claimed MRP
Avoid the subtract-the-percentage trap
Quick, free and private in your browser

Formula used

Original = final ÷ (1 + change ÷ 100).

Examples

Price before 18% GST

Input: Final amount 1180, Applied change 18

Result: 1,000 The item cost ₹1,000 before 18% GST was added.

Original price before a 20% discount

Input: Final amount 2400, Applied change -20

Result: 3,000 A ₹2,400 sale price after 20% off means the original price was ₹3,000.

Salary before a 12% hike

Input: Final amount 56000, Applied change 12

Result: 50,000 A new salary of ₹56,000 after a 12% increase started at ₹50,000.

Results are estimates for general information, not financial, medical, legal, tax, or property advice. Confirm important figures with the relevant institution or a qualified professional.

Reverse Percentage Calculator: frequently asked questions

How do you calculate the original price before a percentage increase?

Divide the final amount by (1 + percentage ÷ 100). For a ₹1,180 bill that includes 18% GST, the original is 1180 ÷ 1.18 = 1000. This calculator applies that formula automatically. Simply subtracting 18% of 1180 would give 967.60, which is wrong because the 18% was charged on the original price, not on the total.

How do I reverse a discount?

Enter the discount as a negative number in Applied change (%). If you paid ₹2,400 after 20% off, enter 2400 and -20, and the calculator returns 3,000, the original price. The tool divides by (1 − 0.20) = 0.8. This is handy for checking whether a sale tag's claimed MRP is honest.

Can I remove GST from a GST-inclusive price with this?

Yes. Enter the inclusive amount as Final amount and the GST rate, such as 5, 18 or 40, as Applied change. The result is the taxable value, and the GST portion is the final amount minus that result. The Reverse GST Calculator does this split for you, including CGST and SGST. For filed invoices, follow the rounding rules your accounting software or tax advisor uses.

Why can't I enter -100% as the change?

A 100% reduction takes any amount to zero, so there is no single original value that can be recovered from it. For that reason the calculator only accepts changes greater than about -99.999999%, up to a maximum of 10,000%. Entering -100 or lower shows the message 'Applied change (%) must be between -99.999999 and 10,000.'

Is reverse percentage the same as percentage decrease?

No. A percentage decrease measures how much a value fell, while reverse percentage finds where it started. For example, if a price dropped 20% to ₹2,400, the decrease from ₹3,000 is ₹600. Reverse percentage gives you the ₹3,000 starting point. Use a percentage change calculator when you already know both values.