Percentage Calculator: X% of Y & Change

Using the Percentage Calculator (Percentage Laboratory)

Choose a mode above (Value of %, % Of, Change, or Difference), enter your two values, and read the result and Ratio visualizer. Use the article below for formulas, when to use each mode, and real-world examples.

At a glance

Value of %

“What is X% of Y?” Use for discounts, tips, and finding a part of a whole.

% Of

“X is what percent of Y?” Use for test scores, share of total, and proportion.

Change

Percent increase or decrease from one value to another. Use for price changes, growth rates, and before/after.

Difference

Symmetric comparison of two values (no “from” or “to”). Use for A/B tests and comparing two measurements.

Percentage Calculator: What is X% of Y, Percent Change & Difference

Free percentage calculator for “what is X percent of Y,” “X is what percent of Y,” percent increase and decrease, and percent difference. How to calculate percentage and percent change formula with steps. Logic Trace and ratio visualizer. Trusted by students and educators. No sign-up; all calculations run locally.

What This Calculator Does and Who It’s For

Who it’s for

Students and teachers (homework, tests); anyone needing how to calculate percentage or how to find percent increase between two numbers; analysts comparing metrics with percent difference. All calculations run in your browser; no data is sent to any server.
Trust and scope

Formulas follow standard algebra. Division by zero (e.g. whole = 0 in % Of, initial = 0 in Change) is detected and shown clearly in the Logic Trace.

This percentage calculator (also a percent calculator) handles four common percentage tasks in one tool: Value of % (what is X% of Y?), % Of (X is what percent of Y?), percent change (increase or decrease from initial to final), and percent difference (symmetric comparison of two values). Each mode shows a step-by-step Logic Trace and a Ratio visualizer so you can verify the math. Use it as a percent increase calculator, percent decrease calculator, or general percentage calculator with steps.

What Is a Percentage?

A percentage is a number expressed as a fraction of 100. So

X\% = \frac{X}{100}

For example, 20% = 0.20. To find what is 20% of 80, compute (20/100) × 80 = 16. Percentages are used for parts of a whole (e.g. 25% of a budget), rate of change (e.g. 10% increase), and comparisons (e.g. percent difference between two results). This calculator supports all of these in one interface

Percent Change vs Percent Difference: When to Use Which

Percent change answers “how much did it go up or down from a starting value?” It uses the initial value as the reference and is ideal for before/after cases: price changes, growth rates, salary increases. Formula:

\text{Percent Change} = \frac{\text{New} - \text{Initial}}{\text{Initial}} \times 100

Initial cannot be 0. Percent difference answers “how different are these two values, in percent?” It uses the average of the two values and is symmetric—there is no “from” or “to.” Use it when comparing two measurements, two options, or A/B test results. Formula:

\text{Percent Difference} = \frac{|V_1 - V_2|}{(V_1 + V_2)/2} \times 100

If the average is 0, the result is undefined. This calculator offers both modes so you can choose the right one for your question

Formulas: All Four Modes

Value of % (what is X% of Y?)

$\text{Result} = \frac{P}{100} \times \text{Whole}$
Enter the percentage (P) and the whole. Example: 15% of 200 = 30
% Of (X is what percent of Y?)

$\text{Percentage} = \frac{\text{Part}}{\text{Whole}} \times 100$
Enter part and whole; whole cannot be 0. Example: 30 is 15% of 200
Change (percent increase or decrease)

$\text{Percent Change} = \frac{\text{New} - \text{Initial}}{\text{Initial}} \times 100$
Use Initial amount (From) and New amount (To). Initial cannot be 0
Difference (symmetric comparison)

$\text{Percent Difference} = \frac{|V_1 - V_2|}{(V_1 + V_2)/2} \times 100$
Use when there is no single “initial” value

All formulas are shown in the calculator’s Logic Trace when you enter values. Quick reference:

Examples: Tip, Test Score, and Price Change

Tip on a bill (Value of %)

Bill is $45; you want to leave 18%. What is 18% of 45? Use Value of %: 18 and 45 → result 8.10. Tip = $8.10.
Test score as a percent (% Of)

You got 34 out of 40. What percent is that? Use % Of: 34 (part) and 40 (whole) → 85%.
Price increase (Change)

Item was $80, now $96. Percent increase? Use Change: Initial 80, New 96 → 20% increase. The Ratio visualizer shows the base (80) and growth (+16).

Real-world use cases show how to apply each mode and build trust in the result.

Percentage Calculator FAQ

? How do I calculate what is X% of Y?

Use Value of % mode: enter X as the percentage and Y as the whole. Result = (X ÷ 100) × Y. Example: 20% of 100 = 20. The Logic Trace above shows the steps.

? How do I find what percentage X is of Y?

Use % Of mode: enter X (part) and Y (whole). Result = (X ÷ Y) × 100. Example: 25 is 25% of 100. Whole cannot be 0.

? What is the formula for percent change?

Percent change = (New − Initial) ÷ Initial × 100. Use Change mode; enter Initial amount (From) and New amount (To). Positive = increase, negative = decrease. Initial cannot be 0.

? What is the difference between percent change and percent difference?

Percent change uses the initial value as the base—use it for before/after (e.g. price increase). Percent difference uses the average of the two values—use it when comparing two numbers with no “before” (e.g. two measurements). This calculator has both modes.

? What is a percentage?

A percentage is a number out of 100. X% means X⁄100. So 20% of 50 = (20⁄100) × 50 = 10. Use this tool for “what is X% of Y,” “X is what % of Y,” percent change, and percent difference.

Percentage Calculator

Percentage Laboratory

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