Percentage Calculator — % Of, Change & Discount
Free Percentage Calculator — Formula Shown Every Time
Three percentage calculators in one: find what percent A is of B, calculate X% of any value, or compute percentage change between two numbers. Every result shows the exact formula used — no black box, no guessing.
How to Use This Percentage Calculator
Choose the tab that matches your question. All three calculators update instantly as you type — no submit button needed.
- Tab 1 — What % is A of B? Use this to express one number as a percentage of another. Example: “45 students passed out of 200 — what percentage is that?”
- Tab 2 — What is X% of Y? Use this when you know the percentage and want the actual amount. Example: “What is 15% of $300?”
- Tab 3 — Percentage Change Use this to measure increase or decrease between two values. Example: “Price went from $80 to $100 — what percentage increase is that?”
Click any Try an example button to instantly load real-world values and see how the formula works before entering your own numbers.
Percentage Calculator Examples — Real World Scenarios
A jacket costs $120, on sale for $90.
% Change = ((90−120)÷120)×100 = −25% (25% off)
You scored 68 out of 80 marks on a test.
Score = (68÷80)×100 = 85%
Buying a $250 item with 8.5% sales tax.
Tax = 250×(8.5÷100) = $21.25
Salary went from $55,000 to $62,000.
Raise = ((62k−55k)÷55k)×100 = +12.73%
Bill is $85. You want to leave a 18% tip.
Tip = 85×(18÷100) = $15.30
Invested $5,000, now worth $6,200.
Return = ((6200−5000)÷5000)×100 = +24%
Percentage Formulas — Explained Simply
The word “percent” comes from the Latin per centum — meaning “out of one hundred.” Every percentage is just a ratio scaled to 100, which makes comparing different-sized groups or values much easier.
Formula 1: What percentage is A of B?
Formula
Percentage = (A ÷ B) × 100
Divide the part by the whole, then multiply by 100. If 45 students passed out of 200, the pass rate is (45 ÷ 200) × 100 = 22.5%. This works for any ratio — scores, proportions, market share, or conversion rates.
Formula 2: What is X% of Y?
Formula
Amount = Y × (X ÷ 100)
Divide the percentage by 100 to get the decimal form, then multiply by your value. To find 15% of $300: 300 × (15 ÷ 100) = 300 × 0.15 = $45. This is the most common percentage calculation used for tips, discounts, and commissions.
Formula 3: Percentage change
Formula
% Change = [(New Value − Original Value) ÷ |Original Value|] × 100
A positive result means an increase; a negative result means a decrease. The absolute value sign (| |) in the denominator ensures the direction of change is captured correctly even when the original value is negative. This formula is used universally for measuring growth, price changes, and performance differences.
Common percentage equivalents
| Fraction | Decimal | Percentage | Common Use |
|---|---|---|---|
| 1 ÷ 2 | 0.5 | 50% | Half price, 50% off |
| 1 ÷ 4 | 0.25 | 25% | Quarter, 25% discount |
| 1 ÷ 5 | 0.20 | 20% | Standard restaurant tip |
| 1 ÷ 8 | 0.125 | 12.5% | Common sales commission |
| 1 ÷ 10 | 0.10 | 10% | Minimum tip, 10% off |
| 3 ÷ 4 | 0.75 | 75% | Three-quarter mark |
| 1 ÷ 3 | 0.333 | 33.3% | One-third share |
| 2 ÷ 3 | 0.667 | 66.7% | Two-thirds majority |
- 10% of any number: move the decimal point one place left — 10% of 350 = 35
- 5%: find 10% then halve it — 5% of 350 = 17.5
- 1%: move the decimal two places left — 1% of 850 = 8.5
- 20%: find 10% and double it — 20% of 350 = 70
- 25%: divide by 4 — 25% of 200 = 50
- 15%: find 10% + 5% and add them — 15% of 80 = 8 + 4 = 12
When Do You Need a Percentage Calculator?
Shopping and discounts
Retailers advertise “30% off” or “save $45” — but rarely both. Our calculator lets you verify any discount claim in seconds. Enter the original price and the discount percentage to find the exact saving. Or enter original and sale prices to find the true discount percentage and compare deals across stores.
School, college and academic use
Convert raw marks to percentages instantly. Whether your exam is out of 80, 120, or any other total, enter your score and the maximum marks to get your percentage. Many grading systems use percentage thresholds — knowing whether you’re at 74.5% vs 75% can determine your letter grade or honours classification.
Finance and business
Calculate profit margins, return on investment, revenue growth, and year-over-year changes. If your business made $320,000 in revenue and $48,000 in profit, the profit margin is (48,000 ÷ 320,000) × 100 = 15%. The percentage change calculator tracks growth rates between any two periods.
Everyday money tasks
Tips at restaurants, splitting shared bills, calculating VAT or GST on purchases, figuring out how much interest you’re paying, or understanding what percentage of your income goes to rent — percentages are everywhere in daily financial life.
Data and statistics
Survey results, poll data, and statistics are almost always expressed as percentages. If 1,247 out of 3,500 survey respondents agreed with a statement, that’s (1,247 ÷ 3,500) × 100 = 35.6% agreement. Our calculator handles any numbers, regardless of scale.
Frequently Asked Questions
How do I calculate 20% of a number?
Use Tab 2. Enter 20 in the “Percentage” field and your number in the “Value” field. The result appears instantly. Alternatively, multiply your number by 0.20. Example: 20% of $85 = 85 × 0.20 = $17.
What is the formula for percentage change?
% Change = [(New − Original) ÷ |Original|] × 100. A positive result is an increase; negative is a decrease. Example: price from $50 to $65 = ((65−50)÷50)×100 = +30% increase.
How do I find what percentage one number is of another?
Divide the part by the whole and multiply by 100. Example: 30 out of 150 = (30÷150)×100 = 20%. Use Tab 1 — enter 30 as A and 150 as B.
Can a percentage be more than 100%?
Yes. A percentage over 100% means the part exceeds the whole, which is common in growth scenarios. If sales grew from $100,000 to $250,000, that’s a 150% increase. Our calculator handles any percentage including values over 100%.
How do I calculate a discount percentage?
Discount% = ((Original − Sale) ÷ Original) × 100. Example: was $80, now $60 = ((80−60)÷80)×100 = 25% off. Use Tab 3 — enter 80 as Original and 60 as New Value. The negative result shows the decrease.
What is the difference between percentage and percentile?
A percentage is a ratio out of 100 (you scored 85% on a test). A percentile is a rank showing what percentage of a group scored below you (90th percentile = you scored better than 90% of others). This calculator computes percentages, not percentiles.
Is this percentage calculator free?
Yes, completely free with no limits, no sign-up, and no premium features. Every calculator on Reckonly is free forever.
Does Reckonly store the numbers I enter?
No. All calculations run inside your browser using JavaScript. Your numbers are never sent to any server, logged, or stored anywhere. The moment you close the tab, everything is gone.
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