How to Calculate Percentage with Calculator

Percentages are used in everyday situations, from calculating shopping discounts and exam scores to understanding price changes, taxes, tips, and business expenses. Although the word “percentage” may sound mathematical, working it out is usually straightforward when you know which formula to use.

A calculator can make these calculations faster and reduce arithmetic mistakes. You only need to identify the numbers you have, decide what you want to find, and apply the correct calculation.

This guide explains how to calculate percentages, how to use a calculator for common percentage problems, and how to understand the results.

What Is a Percentage?

A percentage is a way of expressing a number as a fraction of 100. The word percent means “per hundred,” so 25% represents 25 out of every 100.

For example:

• 10% means 10 out of 100.
• 25% means 25 out of 100.
• 50% means half of a whole.
• 75% means three-quarters of a whole.
• 100% represents the entire amount.

Percentages are useful because they make it easier to compare proportions, even when the original numbers are different.

How to Calculate a Percentage With a Calculator

To calculate a percentage of a number, multiply the number by the percentage and divide the result by 100.

Formula:

Percentage of a number = (Percentage ÷ 100) × Number

Example: What is 20% of 150?

1. Enter 20 into your calculator.
2. Multiply it by 150.
3. Divide the result by 100.

20 × 150 ÷ 100 = 30

Therefore, 20% of 150 is 30.

You can also convert 20% to a decimal by dividing it by 100. Then multiply 0.20 by 150 to get the same answer.

How to Find What Percentage One Number Is of Another

Sometimes, you know a part and the total, but you need to find what percentage the part represents.

Formula:

Percentage = (Part ÷ Whole) × 100

Example: You scored 42 marks out of 60. What is your percentage?

1. Divide 42 by 60.
2. Multiply the result by 100.

42 ÷ 60 × 100 = 70%

Your score is 70%.

This method is useful for exam results, survey responses, completed tasks, and other situations where you need to compare a part with a total.

How to Find the Original Number From a Percentage

If you know a part of a number and the percentage it represents, you can calculate the original value.

Formula:

Original number = Part ÷ (Percentage ÷ 100)

Example: 45 is 30% of what number?

1. Divide 30 by 100 to get 0.30.
2. Divide 45 by 0.30.

45 ÷ 0.30 = 150

The original number is 150.

How to Calculate Percentage Increase

A percentage increase tells you how much a value has grown relative to its original amount.

Formula:

Percentage increase = ((New value − Original value) ÷ Original value) × 100

Example: A product’s price increases from $80 to $100. What is the percentage increase?

1. Subtract the original price from the new price: $100 − $80 = $20.
2. Divide the increase by the original price: 20 ÷ 80 = 0.25.
3. Multiply by 100: 0.25 × 100 = 25%.

The price increased by 25%.

To calculate the new amount after a percentage increase, use:

New amount = Original amount × (1 + Percentage ÷ 100)

For example, increasing $80 by 25% gives $100.

How to Calculate Percentage Decrease

A percentage decrease shows how much a value has dropped compared with its original amount.

Formula:

Percentage decrease = ((Original value − New value) ÷ Original value) × 100

Example: A jacket originally costs $120 and is reduced to $90.

1. Calculate the reduction: $120 − $90 = $30.
2. Divide $30 by $120: 30 ÷ 120 = 0.25.
3. Multiply by 100: 0.25 × 100 = 25%.

The price decreased by 25%.

To find the value after a decrease:

New amount = Original amount × (1 − Percentage ÷ 100)

How to Calculate a Discount

A discount reduces the original price of an item by a specific percentage.

Example: A $200 item has a 15% discount.

Discount amount = 200 × 15 ÷ 100 = $30

Final price = $200 − $30 = $170

You can use the calculator’s discount mode to find both the amount saved and the final price.

How to Calculate Tax or Add a Fee

A percentage-based tax or fee is calculated from the starting amount and then added to it.

Example: A purchase costs $250 before an 8% tax.

Tax = 250 × 8 ÷ 100 = $20

Total = $250 + $20 = $270

The same approach can be used for other percentage-based fees, provided the rate is applied to the full starting amount.

How to Calculate a Tip

A tip is often calculated as a percentage of a restaurant bill or service charge.

Example: Your bill is $60 and you want to leave an 18% tip.

Tip = 60 × 18 ÷ 100 = $10.80

Total = $60 + $10.80 = $70.80

The tip calculator mode can help you work out the tip and the total amount together.

How to Calculate Percentage Change

Percentage change measures the difference between an original value and a new value, relative to the original value.

Formula:

Percentage change = ((New value − Original value) ÷ Original value) × 100

Example: Website visits rise from 800 to 1,000.

1. Subtract 800 from 1,000 to get 200.
2. Divide 200 by 800 to get 0.25.
3. Multiply by 100 to get 25%.

The visits increased by 25%.

A positive result indicates an increase, while a negative result indicates a decrease. The original value must not be zero for this formula.

Common Percentage Calculation Mistakes

• Forgetting to divide by 100: When finding a percentage of a number, convert the percentage to a decimal or divide by 100.
• Using the wrong starting value: Percentage increase and decrease are normally measured against the original amount.
• Confusing percentage points with percent change: A change from 20% to 30% is an increase of 10 percentage points, or a 50% relative increase.
• Rounding too early: Keep extra decimal places during intermediate steps and round the final result.
• Treating a discount as the final price: A 20% discount means 20% is removed, not that the customer pays 20% of the original price.

Frequently Asked Questions

How do I calculate 10% of a number?

Divide the number by 10. For example, 10% of 250 is 25.

How do I calculate 20% on a calculator?

Multiply the number by 20 and divide by 100. For example, 20% of 150 is 30.

How do I calculate 5% of a price?

Multiply the price by 5 and divide by 100. For a $200 item, 5% is $10.

How do I calculate a percentage without a percentage button?

Divide the percentage by 100, then multiply it by the number. For example, 15% of 80 is 0.15 × 80 = 12.

How do I calculate a percentage difference between two numbers?

The term “percentage difference” can refer to different formulas. If you are comparing a new value with an original value, use percentage change. If you are comparing two values without treating either as the original, a common method divides the absolute difference by their average and multiplies by 100.

Can a percentage be more than 100%?

Yes. A percentage can exceed 100% when the part is larger than the reference whole, or when a value has increased by more than its original amount.

Calculating percentages becomes easier when you know whether you need to find a part, a total, an increase, a decrease, or a change between two values. Use the calculator above to enter your numbers, choose the calculation type, and review the formula and steps to understand how the answer was reached.