Percentage Calculator
Six dedicated percentage tools. Ask a question in plain English below, or pick a calculator.
Choose a calculator
What is X% of Y?
The classic. Multiply a percentage by a value — tax, commission, down payment.
X is what % of Y?
The reverse lookup. Grades, market share, progress toward a goal.
% Change
Percent increase or decrease between two numbers. Stocks, salaries, year-over-year.
% Increase
Focused calculator for growth — raises, price hikes, compounding. Positive changes only.
% Difference
Symmetric comparison between two values. Lab measurements, survey groups, product specs.
Tip Calculator
Compute tip amount, total, and per-person split. Side-by-side 15/18/20/25% comparison.
Discount
Sale price and total savings on any percentage off. Shop smarter.
Profit Margin
Margin, markup, and profit from cost + selling price. Retailers and freelancers.
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Your Data Never Leaves Your Device
Unlike other calculators that upload your data to remote servers, everything here runs 100% in your browser. Built by a cybersecurity professional who believes privacy shouldn't be optional.
100% Client-Side
All percentage calculations run entirely in your browser. Your numbers never leave your device.
No Server Storage
We don't operate backend servers that process your data. This is a static site served via CDN — there's nowhere to store it.
No Tracking Without Consent
Analytics only activate after you explicitly accept cookies. Decline and we track nothing — zero scripts, zero pixels.
Open Architecture
Built as a static export with no API calls. You can verify this yourself — inspect network traffic and see zero outbound data.
Free Online Percentage Calculator
PercentageFast is a suite of six dedicated percentage calculators: what is X% of Y, X is what % of Y, percentage change, tip calculator, discount calculator, and profit margin calculator. Each tool has its own page with a formula explanation, worked examples, and a dedicated FAQ, so you can quickly understand the math behind the answer.
All calculations run directly in your browser. Your data is never sent to any server. There is no account to create, no cookie banner for tracking, and no ads stealing your attention from the answer. The natural-language input at the top of this page understands plain-English questions like “what is 15% of 200?” and routes to the right calculation automatically.
How percentages work
A percentage is a number expressed as a fraction of 100. The word comes from the Latin “per centum,” meaning “by the hundred.” To calculate X% of Y, multiply Y by X/100. For example, 25% of 200 equals 200 × 0.25 = 50. To find what percentage X is of Y, divide X by Y and multiply by 100. These two operations are inverses of each other and cover the majority of everyday percentage math.