Percentage Formula Reference

A percentage is a number expressed as a fraction of 100. Understanding percentage formulas allows you to solve any type of percentage problem quickly and accurately.

1. What is X% of Y? → Result = (X ÷ 100) × Y
2. X is what % of Y? → % = (X ÷ Y) × 100
3. % Change (old→new) → % = ((New−Old) ÷ Old) × 100
4. Increase by X% → New = Original × (1 + X/100)
5. Decrease by X% → New = Original × (1 − X/100)

Common Percentage Calculations

Problem	Formula	Example	Answer
25% of 200	200 × 0.25	Discount on $200 item	50
15 is what % of 60	(15÷60)×100	Score out of 60	25%
$50 → $65 change	((65−50)÷50)×100	Price increase	30%
$200 + 20%	200 × 1.20	Tax or markup	$240
$200 − 15%	200 × 0.85	Sale discount	$170

Mental Math Shortcuts

10%: Move decimal left once — 10% of 350 = 35
5%: Find 10% then halve it — 5% of 80 = 4
25%: Divide by 4 — 25% of 200 = 50
50%: Divide by 2 — 50% of 340 = 170
1%: Move decimal left twice — 1% of 850 = 8.50

Real-World Uses

Shopping: Calculate sale prices, discounts, and savings instantly
Finance: Tax rates, interest percentages, investment returns
Grades: Convert marks to percentages (45 out of 60 = 75%)
Tips: Calculate restaurant tips (15%, 18%, 20%)
Statistics: Express proportions and survey results as percentages

How to Calculate Percentage

A percentage is a way of expressing a number as a fraction of 100. The word "percent" comes from the Latin "per centum," meaning "per hundred." Percentages are used in everyday life — from calculating discounts and tax to tracking grades and statistics.

Percentage Formulas

What is X% of Y? → Result = (X / 100) × Y

X is what % of Y? → Percentage = (X / Y) × 100

Percentage Change = ((New − Old) / Old) × 100

Increase by X% → New = Original × (1 + X/100)
Decrease by X% → New = Original × (1 − X/100)

Percentage Examples

25% of 200 = 50 (200 × 0.25)
50 is 25% of 200 ((50/200) × 100 = 25)
100 to 150 = 50% increase ((150-100)/100 × 100)
500 increased by 20% = 600 (500 × 1.20)

Percentage Calculator