🧮 Percentage Calculator
Quick Percentages for Everyday Math
What Is the Percentage Calculator?
Percentage Calculator is a free, browser-based math tool that handles four common percentage operations: finding what a given percentage of a number is, determining what percent one number is of another, calculating percentage change between two values, and reversing a percentage to find the original number. It solves the problem of performing everyday percentage math quickly without needing a separate calculator app or remembering formulas. No downloads, no sign-ups — everything runs locally in your browser.
Key Features
- Four Calculation Modes: Choose from Find % of, What %, % Change, and Reverse % — all four common percentage operations in one tool.
- Instant Results: Results update as you type — no button to press, no waiting. The formula used is shown alongside the answer.
- One-Click Copy: Copy any result to your clipboard with a single click, along with the formula for your reference.
- Privacy-First: All calculations run locally in your browser. Your numbers are never uploaded, stored, or shared.
📋 When to Use the Percentage Calculator
Whether you're calculating a tip at a restaurant, figuring out a sale discount, analyzing grade scores, tracking business growth, or working out reverse tax calculations, this Percentage Calculator gives you instant answers. It's essential for students checking homework, shoppers comparing deals, freelancers computing commissions, and anyone who needs quick percentage math without mental arithmetic or a physical calculator.
⚙️ How the Percentage Calculator Works
The Percentage Calculator uses four standard percentage formulas:
- Find % of: (Percentage / 100) × Number. For example, 15% of 200 = (15/100) × 200 = 30.
- What %: (Part / Whole) × 100. For example, 30 out of 200 = (30/200) × 100 = 15%.
- % Change: ((New − Old) / Old) × 100. Positive = increase, negative = decrease. For example, (75 − 50) / 50 × 100 = 50% increase.
- Reverse %: Value / (Percentage / 100). For example, 30 is 15% of 30 / (15/100) = 200.
How to Use the Percentage Calculator
- Choose your calculation type: Tap one of the four tabs at the top — Find % of, What %, % Change, or Reverse %. The input fields update automatically.
- Enter your numbers: Type the values into the labeled input fields. The tool accepts decimal numbers with standard precision.
- Read the result: The answer appears instantly below the inputs. The formula used is shown in smaller text for transparency.
- Copy the result: Click the 📋 Copy button next to the result to copy both the value and formula to your clipboard.
Frequently Asked Questions
How do I calculate a percentage of a number?
Use the 'Find % of' tab. Enter the percentage (e.g., 15) and the number (e.g., 200). The calculator multiplies the number by the percentage divided by 100: 15% of 200 = 200 × (15/100) = 30.
How do I find what percent one number is of another?
Use the 'What %' tab. Enter the part (e.g., 30) and the whole (e.g., 200). The calculator divides the part by the whole and multiplies by 100: 30/200 = 15%. This is useful for calculating scores, progress, and proportions.
How is percentage change calculated?
Use the '% Change' tab. Enter the old value and the new value. The formula is: ((New − Old) / Old) × 100. A positive result means an increase, a negative result means a decrease. For example, 50 to 75 = (75−50)/50 × 100 = 50% increase.
How do I reverse a percentage?
Use the 'Reverse %' tab. If you know that 30 is 15% of some number, enter 30 as the part and 15 as the percentage. The calculator divides the part by (percentage/100): 30 / (15/100) = 200. This tells you the original whole value.
Is this Percentage Calculator free and private?
Yes, the ToolStand Percentage Calculator is completely free with no sign-up or download required. All calculations happen locally in your browser — your numbers never leave your device.
Does this Percentage Calculator work on mobile?
Yes, the Percentage Calculator works on all devices — phone, tablet, laptop, and desktop. It is responsive and mobile-friendly, with large touch-friendly input fields. It works in all modern browsers including Chrome, Safari, Firefox, and Edge.
Can I use decimal numbers?
Yes, all input fields accept decimal numbers. The calculator rounds results to two decimal places for readability. The exact formula is displayed next to each result so you can verify the calculation.
What is the difference between percentage of and percentage change?
'Find % of' calculates a portion of a number (e.g., 10% of 200 = 20). '% Change' measures the difference between two values as a percentage of the original (e.g., 200 to 220 = 10% increase). They serve different purposes: one finds a fraction, the other measures growth or decline.