Percentage Calculator — 4 Modes, Instant Results

What this percentage calculator does

This English-language percentage calculator handles the four calculations people reach for most: finding X% of a number, figuring out what percent one number is of another, computing a percent change from one value to another, and adding or subtracting a percentage from a number. Each mode shows the formula alongside the result — so you can verify the math rather than trust a black box. U.S. tipping averaged 19.6% in 2024 according to Square's Quarterly Report, which means a quick percentage check is something millions of people do every day at the dinner table. Whether you're computing a discount, a year-over-year growth rate, or a markup, this tool covers it. 100% client-side — your data never leaves your browser. No uploads, no tracking, no server logs.

Features

Four modes, one screen. Switch between X% of Y, X is what % of Y, percent change X → Y, and X ± Y% without leaving the page.
Formula always visible. Every result is paired with its formula — e.g. (part / whole) * 100 — so you can audit the math at a glance.
Real-time calculation. Results update as you type. No submit button, no waiting — ideal for quick comparisons and iterative what-if checks.
Percentage increase and decrease. The percent change mode is the fastest way to figure out a percentage increase or determine percentage increase between any two values — from sales figures to server latency.
Discount and markup math. The X ± Y% mode handles sale prices, tax add-ons, and markups in one step. For deeper discount workflows, the [Discount Calculator](/en/discount-calculator/) goes further.
Privacy by design. All arithmetic runs locally in your browser using JavaScript. No numbers are sent to any server, ever.

How to use the percentage calculator

Pick the mode that matches your question, enter your two numbers, and read the result. Each field has a placeholder to guide you.

Choose a mode. Select from the four tabs: X% of Y, X is what % of Y, % change X → Y, or X ± Y%.
Enter your numbers. Type into the First number and Second number fields. Results appear immediately — no Enter key needed.
Read the formula. The Formula row shows the exact expression used — equivalent to (part / whole) * 100 for the 'what percent' mode, or =A1/B1*100 if you prefer to replicate it in a spreadsheet.
Clear and recalculate. Hit Clear to reset both fields and start a new calculation without reloading the page.

Common use cases

Retail discounts and sales tax. Find the sale price after a 20% discount, then use X ± Y% again to add your state's sales tax — two quick calculations, no mental math.
Year-over-year growth rates. Paste last year's revenue and this year's into the % change mode to compute percentage increase. The tool uses the original value as the denominator, which is the standard definition.
Tip splitting. With U.S. restaurants defaulting to suggested tips of 18–22%, the X% of Y mode gives you the exact dollar amount in one step — no app required.
Statistics and reporting. Translate raw counts to percentages for presentations or dashboards. The 'X is what % of Y' mode covers survey results, conversion rates, and churn figures. The Knight Capital incident postmortem is a reminder that a single misplaced percentage in a financial system can have massive consequences — always verify.
Developer and data work. Quickly validate percentage logic before committing it to code. In Python, round(part/whole*100, 2) is the idiomatic form; this tool lets you sanity-check the expected output before you write the test.

Frequently asked questions

What is the difference between percent change and percentage points?

Percentage points measure an absolute difference between two rates. If an interest rate moves from 5% to 7%, that's a 2 percentage-point increase, but a 40% relative increase. The % change mode here computes the relative version — the one relevant to growth rates and comparisons.

Does a 10% increase followed by a 10% decrease get me back to where I started?

No. A 10% increase on 100 gives 110, and a 10% decrease on 110 gives 99. You end up 1% below the original. This asymmetry matters for investment returns, pricing strategies, and any compounding scenario.

How do I find the percentage increase between two numbers?

Use the % change X → Y mode. Enter the original value as the first number and the new value as the second. The formula is ((new − old) / |old|) × 100. The absolute value in the denominator handles cases where the base is negative, which would otherwise flip the sign incorrectly.

Is my data saved or sent anywhere?

No. Every calculation runs entirely inside your browser with JavaScript. Nothing is transmitted to a server, logged, or stored. You can use this tool offline once the page has loaded.

Can I add a discount and then apply tax — is it the same as doing both at once?

Order matters. Apply the discount first to get the reduced price, then add tax to that reduced amount. Combining them as a single percentage ('10% off + 8% tax = 2% off') is mathematically wrong because the two percentages apply to different base values.

Why does the 'X is what % of Y' formula sometimes give unexpected decimals?

Floating-point arithmetic in JavaScript follows MDN's documentation on Number precision — the underlying IEEE 754 standard means that values like 0.1 + 0.2 evaluate to 0.30000000000000004 internally. This tool rounds the display to avoid surfacing those artifacts.