Percentage Calculator

When to use this

You're looking at a job listing that says "15% annual bonus" and want to know what that actually adds to a $72,000 salary. Or a store is running "35% off everything" and you need the real price before you get to checkout. Maybe your portfolio dropped from $12,400 to $10,800 and you want to know the exact percentage loss. Percentages are everywhere — tips, taxes, grades, discounts, returns — and the mental math is easy to get wrong.

This calculator handles the three percentage problems that come up most often, all in one place. Enter your numbers and the result updates instantly, along with the formula used so you can verify the logic or do it yourself next time. No more Googling "how to calculate percentage change" and scrolling past five ads to find the formula.

It's also a teaching tool. Students working through math or finance problems can see both the answer and the step-by-step calculation. Understanding that "percentage of" is multiplication, "what percent" is division, and "percentage change" is a ratio removes the mystery from a concept that trips people up well into adulthood.

Good to know

Percentage change uses a positive starting value. A zero baseline has no defined percentage change, and negative baselines need context rather than an automatic increase or decrease label. Equal values have 0% change.

Percentage change has a direction. Going from 100 to 150 is a 50% increase. Going from 150 back to 100 is a 33.3% decrease — not 50%. The denominator changes because percentage change is always relative to the starting value. This asymmetry surprises people and is the most common percentage mistake.

"Percentage of" and "percent off" are different operations. "20% of 80" is 16. "20% off 80" is 80 minus 16 = 64. The first is pure multiplication; the second is a discount calculation. Make sure you're solving the right problem.

Percentages can exceed 100%. If your stock went from $50 to $150, that's a 200% increase. If your website traffic tripled, that's a 200% increase too. "100% more" means doubled, not "all of it."

The formula is always the same pattern. Percentage = (Part / Whole) x 100. Every percentage problem is a rearrangement of this single equation. Finding the part? Multiply. Finding the whole? Divide. Finding the percent? Divide and multiply by 100.

Quick Reference

Scenario	Formula	Example
What is X% of Y?	(X / 100) x Y	15% of 200 = 30
X is what % of Y?	(X / Y) x 100	30 is 15% of 200
% increase	((New - Old) / Old) x 100	200 to 250 = +25%
% decrease	((Old - New) / Old) x 100	250 to 200 = -20%
Sale price after discount	Price x (1 - Discount/100)	$80 at 25% off = $60
Price before tax	Total / (1 + Tax/100)	$108 with 8% tax = $100