How to Use a Reverse Percentage Calculator
Reverse percentage works backwards. You've got the final number after a percentage was applied — now you want the original. Sale price and want the pre-discount sticker? Total after tax and need the pre-tax amount? This does that.
Steps
Enter the final amount
Enter the number you've got — the one with the percentage already baked in. Shirt costs $68 after a 20% discount? Enter 68.
Enter the percentage that was applied
Now enter the percentage that was applied. 20% discount? Enter 20, select 'decrease.' Price includes 8% sales tax? Enter 8, select 'increase.' That's it.
Get the original number
The calculator does the proper division to find the original. That $68 shirt? Originally $85. Not $81.60, which is what you'd get if you just added 20% back to 68. This trips people up because the base number changes.
Verify the result
You also get a verification: original times percentage equals the final. So $85 minus 20% = $85 - $17 = $68. Seeing the forward math confirms the reverse calculation was right.
Common Reverse Percentage Scenarios
Reverse percentage shows up more than you'd expect. Shopping: store shows the sale price and discount percentage — what was the original sticker? Taxes: receipt total includes sales tax and you want the pre-tax subtotal. Investments: your portfolio grew 15% to $11,500 — what did you put in originally? ($10,000.) Business costs rose 12% to $67,200 — what were they before the increase? ($60,000.) In every one of these cases, the gut-instinct approach (just subtract the percentage) gives the wrong answer. The actual formula: original = final / (1 +/- percentage/100). The reverse percentage calculator handles it so you don't need to remember the math.
Frequently Asked Questions
Because the 20% was applied to the original number, not the discounted one. 20% of $85 is $17 — that's how you got $68. But 20% of $68 is only $13.60. Add that back and you get $81.60. Wrong. The base number is different. Reverse percentage divides by (1 - rate) or (1 + rate) instead of simply adding or subtracting.
Divide the VAT-inclusive price by (1 + VAT rate). UK VAT at 20%: take £120, divide by 1.20, get £100 pre-VAT. The VAT portion is £20. Or just enter £120 in the calculator, set 20% increase, and let it do the division.