Percentage Calculator

Calculate percentages instantly with our free online Percentage Calculator. Find what percent of a number is, percentage difference, change, and more — all 100% client-side.

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Percentage Calculator

This free online percentage calculator handles five common percentage scenarios instantly in your browser, with no signup, no ads, and no server uploads.

What is a percentage? In mathematics, a percentage is a number or ratio that represents a fraction of 100. It is one of the ways to represent a dimensionless relationship between two numbers; other methods include ratios, fractions, and decimals. Percentages are often denoted by the symbol "%" written after the number. For example, 35% is equivalent to the decimal 0.35, or the fraction $\frac{35}{100}$.

Percentages are computed by multiplying the value of a ratio by 100. For example, if 25 out of 50 students in a classroom are male, the value of the ratio is $\frac{25}{50} = 0.5$, and multiplying this by 100 yields $0.5 \times 100 = 50\%$. In other words, 50% of the students are male.

Percentage formula Although the percentage formula can be written in different forms, it is essentially an algebraic equation involving three values: $P \times V_1 = V_2$, where $P$ is the percentage (expressed as a decimal), $V_1$ is the base value that the percentage modifies, and $V_2$ is the result.

For example, finding 5% of 200: $0.05 \times 200 = 10$.

If solving for the percentage: $P = \frac{V_2}{V_1}$. For example, what percentage of 30 is 1.5? $P = \frac{1.5}{30} = 0.05 = 5\%$.

Percentage difference formula The percentage difference between two values is calculated by dividing the absolute value of the difference by the average of the two numbers, then multiplying by 100:

$$\text{Percentage Difference} = \frac{|V_1 - V_2|}{\frac{V_1 + V_2}{2}} \times 100$$

For example, the percentage difference between 10 and 6:

$$\frac{|10 - 6|}{\frac{10 + 6}{2}} = \frac{4}{8} = 0.5 = 50\%$$

Unlike percentage change, this measure is symmetric — the difference between 6 and 10 is also 50%.

Percentage change formula Percentage increase and decrease are calculated by computing the difference between two values and comparing that difference to the initial value:

$$\text{New Value} = \text{Original} \times (1 \pm \frac{\text{Percent}}{100})$$

For an increase, use $(1 + \frac{P}{100})$. For a decrease, use $(1 - \frac{P}{100})$.

Example — 500 increased by 10%: $500 \times (1 + 0.10) = 550$.

Example — 500 decreased by 10%: $500 \times (1 - 0.10) = 450$.

How to use this calculator Select a calculation mode using the tabs at the top of the calculator panel. Type your numbers into the labeled fields. The result updates live as you type — a debounced calculation runs roughly 180 ms after you stop typing. You can also click the Calculate button or press Ctrl+Enter.

Each result shows a large value, a plain-English explanation, and a step-by-step mathematical breakdown. The Recent Calculations panel remembers your last six results and persists them in your browser's local storage across sessions.

Privacy & Performance All calculations run locally in your browser. No data is transmitted, logged, or stored on any server. Results appear instantly as you type, with no page reloads.

🔒 Client-side only⚡ Web Worker processing🌐 Works offline🛡️ Zero server logs

Frequently Asked Questions

Got questions about percentages, formulas, or how to use this tool? We've got answers.

How do I calculate a percentage of a number?

Multiply the number by the percentage divided by 100. To find 10% of 100, calculate 100 × (10 ÷ 100) = 10. Use the "% of a Number" tab above and enter the percentage and the number to get this instantly, along with the step-by-step breakdown.

What's the difference between percentage change and percentage difference?

Percentage change is directional and measured from a starting value — it tells you how much something grew or shrank from where it began. Percentage difference is symmetric and compares two values against their average, without treating either one as the "original." Use percentage change for things like price increases or growth over time, and percentage difference when comparing two measurements with no clear "before."

How do I calculate a percentage increase or decrease?

For an increase: new value = original × (1 + percent ÷ 100). For a decrease: new value = original × (1 − percent ÷ 100). The "% Increase / Decrease" tab above handles both directions — just choose increase or decrease from the dropdown.

Why do my numbers need to be typed as plain digits, not with a % sign?

The % symbol is already implied by the field label (for example, "is what % of"), so typing it again would be redundant and could cause a parsing error. Just enter the number itself, like 10 rather than 10%.

What is the percentage formula?

The percentage formula is P × V1 = V2, where P is the percentage (as a decimal), V1 is the original value, and V2 is the result. For example, 5% of 200: 0.05 × 200 = 10. This calculator uses this fundamental relationship across all five modes, automatically converting between percentages and decimals as needed.

Can I use this for business calculations like tax or discounts?

Yes. The "% of a Number" mode calculates sales tax, tips, or any percentage-based amount. The "% Increase / Decrease" mode is ideal for markup, discount, and growth calculations. You can copy individual results or keep a running history in the panel below the calculator.

How accurate are the results?

Results are computed using standard JavaScript number arithmetic with up to 4 decimal places of precision. This is sufficient for the vast majority of everyday, educational, and business calculations. For extremely large or high-precision scientific computations, results may be limited by the underlying floating-point representation.