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Percent Calculator

Formula: P% × N = (P/100) × N
Formula: (A/B) × 100%
Formula: ((New − Original) / Original) × 100%
Formula: ((B − A) / A) × 100%

🔹 What Is a Percentage?

A percentage expresses a ratio “per 100.” Writing 37% is the same as 37 out of 100 (i.e., 37/100 or 0.37). Percentages let you quickly compare parts of different-sized wholes—useful in finance, shopping, statistics, and health tracking.

Try our related tools for health and budgeting: BMI Calculator, Calorie Calculator, Body Fat Calculator, BMR Calculator.

🔹 Core Percentage Formulas

  • Find P% of N: (P / 100) × N
  • What percent is A of B? (A / B) × 100%
  • % Increase/Decrease (A → B): ((B − A) / A) × 100%
  • Find the whole given part & percent: Whole = Part ÷ (P / 100)

🔹 Worked Examples

Scenario Setup Work Answer
Find 15% of 200 P = 15, N = 200 (15/100) × 200 30
What % is 30 of 120? A = 30, B = 120 (30/120) × 100% 25%
Price rises from €80 to €92 Original = 80, New = 92 ((92−80)/80) × 100% 15% increase
Weight drops from 250 to 212.5 A = 250, B = 212.5 ((212.5−250)/250) × 100% −15% (decrease)

Want more number tools? Try our Fraction Calculator or Scientific Calculator.

🔹 Common Pitfalls & Tips

  • Percent of vs. percent points: From 10% to 12% is a 2 percentage-point rise, which is a 20% increase relative to 10%.
  • Two-step discounts compound: 20% off, then 30% off is not 50%—it’s 0.8 × 0.7 = 0.56, i.e., 44% off total.
  • Divide by the correct base: In “A is what % of B,” B is the base.
  • Negative results signal decreases: A negative % change means a drop from the original.

🔹 Converting % ⇄ Decimals ⇄ Fractions

Form Convert To Rule Example
Percent → Decimal Decimal Divide by 100 37% → 0.37
Decimal → Percent Percent Multiply by 100 0.125 → 12.5%
Percent → Fraction Fraction p% = p/100, then simplify 25% = 25/100 = 1/4
Fraction → Percent Percent (a/b) × 100% 3/8 = 0.375 = 37.5%

🔹 Everyday & Business Use Cases

  • Shopping: Discounts (e.g., 15% off), VAT additions.
  • Finance: Savings rates, loan APR, investment returns (see your Scientific Calculator for quick math).
  • Health & Fitness: Body composition changes, calorie adjustments (use the Calorie Calculator).
  • Data & Reports: Market share, growth rates, KPIs.

🔹 References & Sources

Source Type What We Used It For Link
Khan Academy – Percent basics Educational site Definitions & foundational examples khanacademy.org
CK-12 – Percent concept Open textbook Concept reinforcement & practice styles ck12.org
OECD Data – Percentage change notes Official data portal Percentage change usage conventions data.oecd.org

🔹 FAQ

▾ What’s the quickest way to find P% of a number?
Multiply by P/100. Example: 18% of 250 = 0.18 × 250 = 45.
▾ How do I tell % increase from percentage points?
% increase compares relative change vs. the original. Percentage points measure the absolute difference between two percentages. From 10% to 12% is +2 percentage points, which is a 20% increase relative to 10%.
▾ What percent is A of B if B = 0?
Undefined, because division by zero isn’t allowed. Our calculator will warn you if the base is 0.
▾ Are two consecutive discounts additive?
No. They compound. A 20% discount then 30% discount equals 0.8 × 0.7 = 0.56 → 44% total, not 50%.
▾ How do I reverse a percentage to find the original price?
If €85 is after a 15% discount, original = 85 ÷ 0.85 = €100.
▾ Does the tool accept commas or % signs?
Yes—inputs like “1,200” or “15%” are accepted. We sanitize inputs for you.
▾ Can I calculate negative changes?
Yes. If the new value is lower than the original, the result is a negative percentage, indicating a decrease.