Percentage of a Number Calculator
Calculate percentages, find missing values, and work out percentage increases or decreases.
Your result
20 ÷ 100 × 150 = 30
This calculator provides mathematical results based on the values entered. Currency symbols are for display only and are not a currency conversion service.
Calculating a percentage is useful for everyday tasks, from working out a shopping discount to checking a test score or adjusting a budget. A percentage of a number calculator helps you find the answer without having to work through the formula manually.
Use the calculator above to find a percentage of a value, work out what percentage one number is of another, recover an original value, or calculate an increase or decrease. It also shows the formula used, so you can understand how the result was reached.
How to Calculate a Percentage of a Number
To find a percentage of a number, divide the percentage by 100 and multiply the result by the number.
Formula:
Percentage of a number = (Percentage ÷ 100) × Number
For example, to calculate 20% of 150:
- Divide 20 by 100 to get 0.20.
- Multiply 0.20 by 150.
- The result is 30.
Therefore, 20% of 150 is 30.
You can use this formula with whole numbers, decimals, and negative values.
How to Use the Calculator
- Choose the type of calculation you need from the dropdown menu.
- Enter the two values in the input fields. Their labels change based on the selected calculation.
- Select a number format. Choose plain numbers or a currency display if your calculation involves money.
- Review the result and the formula shown underneath.
- Use the copy button to save the result or reset the calculator for another calculation.
Currency formatting changes how the result appears, but it does not convert between currencies.
Different Types of Percentage Calculations
Find a percentage of a number
This calculation finds a specific portion of a value. For example, 15% of 200 is 30.
Formula: (15 ÷ 100) × 200 = 30
It is useful for calculating portions, discounts, tips, and percentage-based amounts.
Find what percentage one number is of another
If you know the part and the total, you can calculate the percentage represented by the part.
Formula:
(Part ÷ Whole) × 100
For example, if you scored 42 marks out of 60:
(42 ÷ 60) × 100 = 70%
Your score is 70% of the total marks.
Find the original number
Sometimes you know the percentage and the resulting amount, but not the original total. You can calculate the whole by dividing the known part by the percentage expressed as a decimal.
Formula:
Whole = Part ÷ (Percentage ÷ 100)
For example, if 30 represents 20% of a number:
30 ÷ 0.20 = 150
The original number is 150.
Increase a number by a percentage
To increase a value by a percentage, calculate the percentage amount and add it to the original number.
Formula:
New value = Original × (1 + Percentage ÷ 100)
For example, increasing 150 by 20% gives:
150 × 1.20 = 180
The new value is 180.
Decrease a number by a percentage
To decrease a value by a percentage, subtract the percentage amount from the original number.
Formula:
New value = Original × (1 − Percentage ÷ 100)
For example, decreasing 150 by 20% gives:
150 × 0.80 = 120
The new value is 120.
A decrease greater than 100% can produce a negative result. This is mathematically valid, though it may not be meaningful for every real-world situation.
Calculate percentage increase or decrease
Percentage change compares a new value with an original value.
Formula:
Percentage change = ((New value − Original value) ÷ |Original value|) × 100
For example, if a value changes from 100 to 125:
((125 − 100) ÷ 100) × 100 = 25%
This represents a 25% increase. If the new value were 75 instead, the result would be a 25% decrease.
The original value must not be zero because percentage change from a zero baseline is undefined.
Practical Percentage Examples
| Situation | Calculation | Result |
|---|---|---|
| 10% of 250 | 250 × 0.10 | 25 |
| 35% of 80 | 80 × 0.35 | 28 |
| 45 is what percentage of 180? | 45 ÷ 180 × 100 | 25% |
| 60 is 30% of what number? | 60 ÷ 0.30 | 200 |
| Increase 400 by 15% | 400 × 1.15 | 460 |
| Decrease 500 by 12% | 500 × 0.88 | 440 |
| Change from 80 to 100 | (100 − 80) ÷ 80 × 100 | 25% increase |
Where Percentages Are Used
Percentages are used in many everyday calculations, including:
- Shopping: Find the amount saved during a sale or discount.
- Education: Calculate test scores, grades, or marks earned.
- Budgeting: Work out how much of a budget is assigned to a category.
- Business: Calculate changes in sales, costs, or other business figures.
- Personal finance: Calculate percentage-based fees, interest amounts, or price changes. Financial products may use additional rules that a basic percentage calculator does not model.
Common Percentage Calculation Mistakes
Confusing the part with the whole
When finding what percentage one number is of another, make sure the total is used as the denominator. Dividing the whole by the part will usually produce a different result.
Forgetting to divide by 100
A percentage must be converted to a decimal before multiplying. For instance, 25% is 0.25, not 25.
Mixing up percentage points and percentage change
A rise from 20% to 25% is an increase of 5 percentage points. Relative to the original 20%, it is a 25% increase. These describe different things.
Using zero as the original value
A percentage change calculation cannot use zero as the original baseline because division by zero is undefined.
Frequently Asked Questions
How do I calculate 20% of a number?
Multiply the number by 0.20. For example, 20% of 150 is 150 × 0.20 = 30.
How do I find 5% of a number?
Convert 5% to 0.05 and multiply it by the value. For example, 5% of 300 is 15.
How do I find what percentage 30 is of 150?
Divide 30 by 150 and multiply by 100. The result is 20%.
How do I find the original number if I know 20% is 30?
Divide 30 by 0.20. The original number is 150.
Can I calculate percentages of decimals or negative numbers?
Yes. The formulas support decimals and negative values. However, interpret the result according to the context, as negative values may not make sense for every type of calculation.
Does the calculator convert USD to other currencies?
No. Currency options only format the result in USD, INR, EUR, GBP, CAD, or AUD. They do not perform currency exchange conversions.
Percentages help express portions, compare values, and measure increases or decreases. Whether you are calculating a discount, checking a score, or finding an unknown original amount, choosing the correct formula is the key to getting an accurate result.
Use the calculator above to solve common percentage problems, view the calculation steps, and copy the answer for later reference.