MATH & PROBLEM SOLVING
Reverse Percentage
Calculator
Find the original whole number when you only know the part and its percentage.
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Instant results
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Step-by-step math
REVERSE PERCENTAGE
Find the original number
Amount
Example: 45 (the known part)
%
Example: 15% of the whole
THE ORIGINAL WHOLE NUMBER IS
300
45 is 15% of what number?
45 ÷ (15 ÷ 100) = 300
45 ÷ (15 ÷ 100) = 300
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How Reverse Percentage Works
Reverse percentage helps you find the original whole number when you only know a part and the percentage it represents.
The Formula
Original Whole = Part ÷ (Percentage ÷ 100)
Example: 45 is 15% of what number?
45 ÷ (15 ÷ 100) = 45 ÷ 0.15 = 300
45 ÷ (15 ÷ 100) = 45 ÷ 0.15 = 300
Step-by-Step Method
STEP 1
Convert % to Decimal
Divide the percentage by 100.
Example: 15% → 0.15
Example: 15% → 0.15
STEP 2
Divide the Part
Divide the known amount by the decimal.
Example: 45 ÷ 0.15
Example: 45 ÷ 0.15
STEP 3
Get the Whole
The result is the original number.
Example: 300
Example: 300
Real-Life Examples
DISCOUNT / SALE PRICE
After 20% discount, the price is $80
What was the original price?
80 ÷ (20 ÷ 100) = $100
EXAM / TEST SCORE
You scored 36 marks which is 75% of total
What are the total marks?
36 ÷ (75 ÷ 100) = 48 marks
TAX / COMMISSION
You received $540 after 10% tax was deducted
What was your gross amount?
540 ÷ (10 ÷ 100) = $600
DATA ANALYSIS
120 people represent 40% of total respondents
What is the total number of respondents?
120 ÷ (40 ÷ 100) = 300 people
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Frequently Asked Questions
What is reverse percentage? ↓
Reverse percentage is when you know a part and the percentage it represents, but you need to find the original whole number.
It is the opposite of normal percentage calculations.
When should I use a reverse percentage calculator? ↓
Use it when working backwards from discounts, taxes, commissions, grades, or any situation where you know the result after a percentage was applied.
Common in shopping (original price after discount) and academics (total marks from percentage).
How is reverse percentage different from normal percentage? ↓
In normal percentage, you know the whole and want to find the part. In reverse percentage, you know the part and the percentage, and want to find the whole.
The formula is different: you divide instead of multiply.
Can I use this for finding original price after discount? ↓
Yes! This is one of the most common uses. If the sale price is $80 after 20% discount, enter 80 as the part and 20 as the percentage.
The calculator will give you the original price of $100.