Percentage Calculator
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Editorial Review
Publisher
DP Tech Studio
Last reviewed
April 22, 2026
We keep this page accurate and in plain language — by DP Tech Studio.
Reference sources
Important: Percentage change from zero is undefined, and financial or tax results may require additional context beyond a simple percentage formula.
Three Percentage Problems, One Tool
This calculator handles the three percentage questions that come up most often. Choose the mode that matches your question — the tool does the arithmetic instantly.
Percentages show up everywhere: shopping discounts, exam scores, salary increases, tax amounts, growth rates, and loan interest. If you find yourself reaching for a calculator whenever a percentage is involved, the modes below cover the most common situations.
The Three Calculation Modes
- What is X% of Y? — Use this to find a portion of a value. For example, "What is 20% of 500?" → 100. Formula:
(X / 100) × Y - X is what % of Y? — Use this to express a part as a percentage of a whole. For example, "100 is what % of 500?" → 20%. Formula:
(X / Y) × 100 - % change from X to Y? — Use this to measure growth or decline. For example, "% change from 400 to 500?" → +25%. Formula:
((Y − X) / X) × 100
Example Calculations
Mode 1 — What is 15% of 2,000?
(15 / 100) × 2,000 = 300
Mode 2 — 75 is what % of 300?
(75 / 300) × 100 = 25%
Mode 3 — % change from 800 to 1,000?
((1,000 − 800) / 800) × 100 = +25%
(15 / 100) × 2,000 = 300
Mode 2 — 75 is what % of 300?
(75 / 300) × 100 = 25%
Mode 3 — % change from 800 to 1,000?
((1,000 − 800) / 800) × 100 = +25%
Everyday Situations Where This Helps
- Shopping discounts — A jacket was $120 and is now 30% off. Mode 1: what is 30% of $120? → $36 saved, so you pay $84.
- Exam scores — You scored 78 out of 120. Mode 2: 78 is what % of 120? → 65%.
- Salary increase — Your pay went from $45,000 to $49,500. Mode 3: % change → 10% rise.
- Tax and VAT — An invoice is $500 plus 18% tax. Mode 1: what is 18% of $500? → $90 tax, total $590.
- Tipping — Your restaurant bill is $68 and you want to leave 15%. Mode 1: 15% of $68 → $10.20 tip.
Common Percentage Mistakes Worth Avoiding
Even simple percentage questions can trip people up. Here are three errors that come up regularly:
- Direction matters for % change — A price rising from $100 to $150 is a 50% increase. But going back from $150 to $100 is only a 33.3% decrease, not 50%, because the base changes. Mode 3 accounts for this automatically when you enter the numbers in the right order.
- Stacking percentages is not additive — A 20% discount followed by a further 10% discount is not a 30% discount. The second 10% applies to the already-reduced price, giving a combined discount of 28%.
- Round at the end, not in the middle — When chaining multiple percentage calculations, keep full decimal precision in intermediate steps. Rounding too early causes small errors to accumulate.
Frequently Asked Questions
Use “What is X% of Y?” when you already know the percentage and want the amount, such as a discount, tip, commission, or tax value on a base price.
Because percentage change divides by the starting value. If the baseline is zero, the expression becomes undefined, so you need a different comparison method for that case.
Yes. It is useful for marks, margins, tax, discounts, conversion rates, growth tracking, and any situation where you need to understand part-to-whole or before-to-after changes.
A percentage of a percentage (sometimes called a basis point in finance) requires two sequential calculations. For example, 20% of 30% = (20/100) × 30 = 6%. So a mutual fund that gains 30% and charges a 20% performance fee retains only 24% of the gain for the investor.
Divide the part by the whole and multiply by 100. For example, a 3:7 ratio means 3 parts out of 10 total, so 3/10 × 100 = 30%. You can verify this directly using mode 2 of this calculator: enter 3 as X and 10 as Y.
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