Reverse Percentage Calculator
To reverse a percentage, divide the known value by the percentage and multiply by 100: original = value ÷ percent × 100.
Last updated 2026-08-14
Embed on your site
Embed this calculator on your site:
<iframe src="https://calculopedia.darzh.xyz/embed/reverse-percentage-calculator/" width="100%" height="700" style="border:0;border-radius:12px" loading="lazy"></iframe>
quizExample
How this calculator works, with real numbers (no JavaScript needed):
Inputs
- The value you know
- 30
- It represents this %
- 15
Results
- Original number
- 200
- The value you entered
- 30
functionsThe formula
Reverse percentage solves the question "30 is 15% of what number?" — you know a part and its percentage, and you want the whole. It's the flip side of the forward percentage calculation.
The formula
Original = known value × 100 ÷ percent
Worked example
30 is 15% of what?
30 × 100 ÷ 15 = 3000 ÷ 15 = 200
So 30 is 15% of 200. The calculator uses exactly this math.
Why it works
"30 is 15% of X" means X × 0.15 = 30. Dividing both sides by 0.15 gives X = 30 ÷ 0.15 = 200. Multiplying by 100 and dividing by the percent (as a whole number) is the same operation.
Real-world uses
- GST-inclusive prices — ₹11,800 is a price including 18% GST. Here you don't want "X is 18% of what" but rather the base: this is where the GST calculator and reverse-percentage logic overlap.
- Scored marks — "I got 34 out of 40. That's 85%. How many marks was the full exam?" Actually the full exam is given; instead: "34 marks is 85% of the total — what's the total?" → 34 × 100 ÷ 85 = 40.
- Sales commissions — "₹7,500 commission is 5% of sales. What were sales?" → 7,500 × 100 ÷ 5 = ₹1,50,000.
- Test prep and budgeting — working back from a known portion to the whole.
helpFrequently asked questions
question_markHow do I reverse a percentage?
Divide the known value by the percentage and multiply by 100: original = value ÷ percent × 100. For example, 30 ÷ 15 × 100 = 200.
question_mark30 is 15% of what number?
30 × 100 ÷ 15 = 200. So 30 is 15% of 200.
question_markWhat is the reverse percentage formula?
Original number = known value × 100 ÷ percent. Use it when you know a part and the percentage it represents, and you want the whole.