What Is This Tool?
A percentage expresses a number as a fraction of 100 — 25% means 25 out of every 100. The three questions people actually need to answer are: "what is 20% of 350?" (percentage of a number), "48 is what percent of 60?" (ratio as a percentage), and "the price went from 80 to 95 — what's the change in percent?" (percentage change).
Each has its own small formula, and mixing them up is the most common percentage mistake. This tool keeps them as three separate, clearly-labeled calculators so you always use the right one.
Why Use It?
- All three everyday percentage questions on one page, clearly separated.
- Live results — numbers update as you type, no button pressing.
- Percentage change shows a signed result (+/-), so increases and decreases are unambiguous.
- Handles decimals and negative numbers correctly.
- Free, instant, mobile-friendly — perfect for shopping and restaurant math.
How to Use
- Pick the block that matches your question.
- Type your two numbers — the result appears immediately.
- First block: 15% of 240 → fill 15 and 240.
- Second block: 45 is what % of 180 → fill 45 and 180.
- Third block: from 80 to 95 → fill 80 and 95 for the percentage change.
Example
Input
What is 15% of 240?Output
36Formula: 240 × (15 ÷ 100) = 36. A 15% tip on a $240 bill is $36.
Frequently Asked Questions
How do I calculate a percentage of a number by hand?
Multiply the number by the percentage divided by 100: 20% of 350 = 350 × 0.20 = 70. Mental shortcut: 10% is one decimal shift (35), then scale — 20% is double that.
How is percentage change calculated?
(new − old) ÷ |old| × 100. From 80 to 95: (95−80)/80 × 100 = +18.75%. A negative result means a decrease. Note the base is always the OLD value — that's the most common error.
Why is a 50% increase not undone by a 50% decrease?
Because the base changes. 100 + 50% = 150, but 150 − 50% = 75. Each percentage applies to its own starting value — this asymmetry trips up even professionals.
What's the difference between percentage points and percent?
Going from 10% to 15% is a rise of 5 percentage points, but a 50% relative increase. News often confuses these; this calculator's third block gives you the relative (percent) change.
How do I calculate a discount price?
Use the first block for the discount amount: 25% of 80 = 20, so the sale price is 80 − 20 = 60. Shortcut: multiply by (100 − discount)%: 80 × 0.75 = 60.