Percentages show up everywhere — discounts, tips, tax, grades, price changes. This calculator covers the three questions people ask most, and shows the formula it used so you can check it.
How to use
- Pick the question that matches what you want to know.
- Enter the two numbers.
- Read the result — it updates as you type.
Why use Deftivo
Three calculators in one
Percent of a number, what percent one value is of another, and percentage increase or decrease.
Shows the working
Every result comes with the formula, which is handy for homework and double-checking.
Instant
No button to press — results update as you type.
The formulas
X% of Y = Y × X ÷ 100. For example, 15% of 80 is 80 × 15 ÷ 100 = 12.
X is what percent of Y = X ÷ Y × 100. For example, 30 out of 120 is 25%.
Percentage change = (new − old) ÷ old × 100. Going from 50 to 65 is a 30% increase; from 80 to 60 is a 25% decrease.
Frequently asked questions
How do I calculate a discount?
Use “What is X% of Y” with the discount rate and the price to get the amount taken off, or “Percentage change” with the old and new price to find the discount rate.
Why is a 50% increase followed by a 50% decrease not the same number?
Because the second percentage is taken from a different base. 100 up 50% is 150; 150 down 50% is 75.
What is the difference between percent and percentage points?
Moving from 10% to 12% is a rise of 2 percentage points, but a 20% increase relative to the starting value.