How to Calculate Percentage Change and Percentages Online
A percentage expresses a number as a fraction of 100. The core formula is: Percentage = (Part / Whole) x 100. To reverse this and find the part, use: Part = Whole x (Percentage / 100). For example, to find 20% of 80, calculate 80 x 0.20 = 16. To find what percentage 25 is of 200, calculate (25 / 200) x 100 = 12.5%. These two operations cover the vast majority of everyday percentage problems — discounts, tips, grades, and ratios.
This calculator offers three modes in one tool. The first mode, 'What is X% of Y?', finds a percentage of a number — useful for calculating tips, discounts, tax amounts, and commissions. The second mode, 'X is what % of Y?', determines what percentage one number represents of another — perfect for grades, test scores, and part-to-whole comparisons. The third mode, 'Percentage Change', calculates the increase or decrease between two values using the formula ((New - Old) / Old) x 100 — essential for tracking stock price changes, revenue growth, or weight loss progress.
Results update in real time as you type, so there is no submit button to press. The calculator handles decimals, negative numbers, and large values accurately. Whether you need to find the percentage difference between two numbers, convert a fraction to a percentage, calculate a grade, or figure out how much you save with a discount, all three modes are accessible from the same page with a single click to switch between them.
Why Use This Free Percentage Change Calculator?
- Three calculation modes in one tool — find a percentage of a number, find what percent one number is of another, or calculate percentage change between two values
- Shows the formula and step-by-step work for every calculation so you can learn the math, not just get the answer
- Real-time results update instantly as you type — no submit button, no page reload
- Handles decimals, negative numbers, and large values accurately for financial, academic, and scientific use
- 100% browser-based — your numbers never leave your device or touch any server
- Works on any device — desktop, tablet, or phone — with no app install or account required
- Clean, distraction-free interface designed for quick everyday calculations
Frequently Asked Questions
How do I calculate a percentage?
Divide the part by the whole and multiply by 100. The formula is: Percentage = (Part / Whole) x 100. For example, to find what percentage 30 is of 120, calculate (30 / 120) x 100 = 25%. To find a percentage of a number (such as 20% of 80), multiply the number by the percentage as a decimal: 80 x 0.20 = 16.
What is the percentage formula?
The basic percentage formula is: Percentage = (Part / Whole) x 100. To find the part when you know the percentage, rearrange to: Part = Whole x (Percentage / 100). To find the whole when you know the part and percentage: Whole = Part / (Percentage / 100). These three forms cover every standard percentage problem.
How do I find a percentage of a number?
Multiply the number by the percentage expressed as a decimal. To convert a percentage to a decimal, divide by 100. For example, 15% of 200 is 200 x 0.15 = 30. Another way: divide the number by 100 first, then multiply by the percentage. So 200 / 100 = 2, then 2 x 15 = 30. Both methods give the same result.
What is 20% of 80?
20% of 80 is 16. Multiply 80 by 0.20 (the decimal form of 20%), which equals 16. Alternatively, divide 80 by 100 to get 0.8, then multiply by 20 to get 16. This same method works for any 'what is X% of Y' question.
What is 15% of 200?
15% of 200 is 30. Calculate: 200 x 0.15 = 30. A quick mental math approach: 10% of 200 is 20, and 5% of 200 is 10, so 15% = 20 + 10 = 30.
What is 10% of 50?
10% of 50 is 5. To find 10% of any number, simply move the decimal point one place to the left. So 50 becomes 5.0, which is 5. This shortcut makes 10% one of the easiest percentages to calculate mentally.
What is 25% of 60?
25% of 60 is 15. Calculate: 60 x 0.25 = 15. A quick shortcut: 25% is the same as one quarter, so divide 60 by 4 to get 15.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value, and multiply by 100. The formula is: Percentage Increase = ((New Value - Old Value) / Old Value) x 100. For example, if a price goes from $50 to $75, the increase is ((75 - 50) / 50) x 100 = 50%. A positive result confirms an increase.
How do I calculate percentage decrease?
Use the same formula as percentage change: ((New Value - Old Value) / Old Value) x 100. When the new value is smaller than the old value, the result is negative, indicating a decrease. For example, if a stock drops from $80 to $60, the change is ((60 - 80) / 80) x 100 = -25%, meaning a 25% decrease. You can also express this as: Percentage Decrease = ((Old - New) / Old) x 100 to get a positive number directly.
How do I find what percentage one number is of another?
Divide the part by the whole and multiply by 100. For example, to find what percent 25 is of 200, calculate (25 / 200) x 100 = 12.5%. This works for any part-to-whole comparison: test scores (42 out of 50 = 84%), completion rates, or budget allocations.
What is the percentage difference between two numbers?
Percentage difference measures the relative gap between two values using their average as the base. The formula is: Percentage Difference = (|Value1 - Value2| / ((Value1 + Value2) / 2)) x 100. For example, comparing 30 and 40: |30 - 40| / ((30 + 40) / 2) x 100 = 10 / 35 x 100 = 28.57%. This differs from percentage change, which uses the old value as the base rather than the average.
How do I calculate a tip?
Multiply the bill amount by the tip percentage as a decimal. A 20% tip on a $50 bill is $50 x 0.20 = $10, making the total $60. For 15%, multiply by 0.15: $50 x 0.15 = $7.50. A quick mental shortcut: find 10% (move the decimal), then add half of that for 15%, or double it for 20%. For more complex tip splitting, try the <a href="/tools/tip-calculator/">Tip Calculator</a>.
How do I calculate a discount?
Multiply the original price by the discount percentage as a decimal to find the savings, then subtract from the original price. For example, a 30% discount on $80: savings = $80 x 0.30 = $24, so you pay $80 - $24 = $56. Alternatively, multiply the original price by (1 - discount rate): $80 x 0.70 = $56 directly.
How do I convert a percentage to a decimal?
Divide the percentage by 100, or equivalently, move the decimal point two places to the left. For example, 75% = 75 / 100 = 0.75. Other examples: 5% = 0.05, 150% = 1.50, 0.5% = 0.005. To convert back from a decimal to a percentage, multiply by 100 (move the decimal two places to the right).
How do I convert a fraction to a percentage?
Divide the numerator by the denominator, then multiply by 100. For example, 3/8 as a percentage is (3 / 8) x 100 = 37.5%. Common fractions to know: 1/2 = 50%, 1/3 = 33.33%, 1/4 = 25%, 1/5 = 20%, 3/4 = 75%, 2/3 = 66.67%. To convert a percentage back to a fraction, put the percentage over 100 and simplify: 75% = 75/100 = 3/4.
How do I convert a percentage to a fraction?
Place the percentage number over 100, then simplify the fraction by dividing both numerator and denominator by their greatest common factor. For example, 60% = 60/100 = 3/5 (dividing both by 20). Another example: 12.5% = 12.5/100 = 125/1000 = 1/8. Some common conversions: 25% = 1/4, 50% = 1/2, 33.33% = 1/3, 20% = 1/5.
What is a percentage point vs. a percentage?
A percentage point is the arithmetic difference between two percentages. A percentage (or percent change) is the relative difference. For example, if an interest rate moves from 10% to 15%, that is a 5 percentage point increase, but a 50% increase (because 5 is 50% of 10). This distinction matters in finance, economics, and statistics — saying 'a 5 percentage point rise' and 'a 50% rise' describe the same event but from different perspectives.
How do I calculate my grade percentage?
Divide the points you earned by the total points possible and multiply by 100. For example, if you scored 42 out of 50, your grade is (42 / 50) x 100 = 84%. For weighted grades, multiply each assignment's percentage by its weight, then sum: if homework (30% weight) is 90% and exams (70% weight) are 80%, your weighted grade is (0.30 x 90) + (0.70 x 80) = 27 + 56 = 83%.
How do I calculate percentage growth?
Percentage growth uses the same formula as percentage increase: ((New Value - Old Value) / Old Value) x 100. For business metrics, if revenue grew from $100,000 to $135,000, the growth rate is ((135,000 - 100,000) / 100,000) x 100 = 35%. For compound growth over multiple periods, use the Compound Annual Growth Rate (CAGR) formula: ((Ending Value / Beginning Value)^(1/n) - 1) x 100, where n is the number of years.
How do I calculate weight loss percentage?
Use the percentage decrease formula with your starting and current weight: ((Starting Weight - Current Weight) / Starting Weight) x 100. For example, if you went from 200 lbs to 185 lbs, your weight loss percentage is ((200 - 185) / 200) x 100 = 7.5%. This metric is more meaningful than pounds lost alone, since a 15-pound loss represents different achievements for a 200-pound person vs. a 300-pound person.
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