Percentage Calculator

What Is a Percentage?

A percentage is a way of expressing a number as a fraction of one hundred. The word comes from the Latin per centum, meaning "by the hundred," and the symbol % simply stands in for "divided by 100." So 25% is another way of writing 25/100, or the decimal 0.25. Percentages let you compare proportions on a common scale regardless of the underlying totals, which is why they appear everywhere from discounts and tax rates to test scores, statistics, and interest rates.

Most everyday percentage questions fall into a handful of patterns: finding a portion of a quantity, expressing one quantity as a share of another, measuring how much a value has grown or shrunk, and applying an increase or decrease to a starting figure. This calculator gives each of those patterns its own card so you can pick the one that matches your question without rearranging formulas yourself. Every result is computed locally in your browser the instant you click Calculate.

How to Use This Percentage Calculator

The tool is split into four independent cards, each answering a different type of question. In What is X% of Y? enter the percentage and the total, then click Calculate to get the portion. In X is what % of Y? enter the part and the whole to find the percentage. In Percentage Change enter a starting and ending value to see the relative increase or decrease. In Percentage Increase/Decrease enter a base value and a percentage, then click Increase or Decrease to apply it.

You can press Enter inside any card's input fields to trigger that card's calculation without reaching for the button. Each card shows its own result directly beneath it, so you can keep several calculations on screen at once for easy comparison.

Real-World Use Cases

• Shopping discounts — work out the dollar value of a "30% off" sale using the X% of Y card.
• Tips and tax — add a 15% tip or a sales-tax rate to a bill with the Increase card.
• Grades and scores — find what percentage 42 correct answers out of 50 represents using the X is what % of Y card.
• Tracking growth — measure the percentage change between last month's and this month's figures.
• Budgeting and markdowns — reduce a price or budget line by a set percentage with the Decrease card.

Tips for Working with Percentages

• To turn a percentage into a decimal, divide by 100; to go the other way, multiply by 100. This makes mental estimates easier.
• Percentage change always uses the original value as the denominator, so a rise from 80 to 100 is a 25% increase, not 20%.
• A percentage increase followed by the same percentage decrease does not return to the start — a 20% rise then a 20% fall leaves you below the original.
• Be careful to distinguish a percentage change from percentage points: rates measured in percent can themselves change by points.
• When comparing two quantities, decide clearly which is the "whole" before computing what percentage the other represents.

Percentage Formulas

• X% of Y = (X / 100) × Y
• X is what % of Y = (X / Y) × 100
• Percentage change = ((New − Old) / |Old|) × 100
• Increase by X% = Value × (1 + X / 100)
• Decrease by X% = Value × (1 − X / 100)

Features

• Four calculation types — percentage of a number, one number as a percentage of another, percentage change, and percentage increase or decrease.
• Decimal support — every field accepts fractional input, so non-whole percentages and values work.
• Enter-key shortcut — press Enter in any card to run that calculation instantly.
• Independent results — each card displays its own answer so multiple calculations stay visible side by side.
• 100% client-side — your data never leaves your browser.

Frequently Asked Questions

How do I calculate a percentage of a number?

Divide the percentage by 100 and multiply by the number. For example, 15% of 200 equals (15 / 100) × 200 = 30. Use the "What is X% of Y?" card to do this automatically.

How do I find what percentage one number is of another?

Divide the part by the whole and multiply by 100. For example, 25 out of 200 is (25 / 200) × 100 = 12.5%. The "X is what % of Y?" card performs this calculation for you.

How is percentage change calculated?

Subtract the old value from the new value, divide by the absolute value of the old value, and multiply by 100. The result is labeled as an increase or a decrease depending on its sign.

What is the difference between percentage change and percentage points?

Percentage change is relative, so going from 50 to 75 is a 50% increase. Percentage points are absolute, so an interest rate moving from 3% to 5% is a 2 percentage-point rise, even though that is a 66.7% relative increase.

Can I use decimal numbers?

Yes. Every input field accepts decimal values, so you can calculate things like 7.5% of 320 or a change between 19.99 and 24.95 without rounding your inputs first.

Are my numbers sent to a server?

No. All four calculators run entirely in your browser using client-side JavaScript, so the values you enter are never transmitted or stored anywhere.