How to Calculate Percentage Instantly — A Simple Guide for Everyday Use

Whether you're working out a discount at the shops, checking how much your salary has increased, or trying to figure out a test score, percentages come up constantly in daily life. Yet many people still find them confusing.
Here's a quick breakdown of the most common percentage calculations:
What is X% of Y?
Multiply Y by X and divide by 100.
Example: What is 20% of 150? → 150 × 20 ÷ 100 = 30
X is what % of Y?
Divide X by Y and multiply by 100.
Example: 45 is what % of 180? → 45 ÷ 180 × 100 = 25%
Percentage increase/decrease
Formula: ((New − Old) ÷ Old) × 100
Example: Price went from $80 to $100 → (100−80) ÷ 80 × 100 = 25% increase
Reverse percentage (finding the original value)
If a jacket is $85 after a 15% discount, the original price is:
$85 ÷ (1 − 0.15) = $85 ÷ 0.85 = $100
These formulas cover most real-world scenarios. If you'd rather skip the manual math, I've been using this free tool that handles all of these modes instantly with no sign-up needed: https://onlinepercentage.net
It covers everything from basic percentage calculations to percentage change, reverse percentage, percent error, and more — all on one page.