how to use calculator to find percentage

Percentages are everywhere: discounts, taxes, grades, interest rates, tips, and data reports. The good news is that you do not need advanced math to work with percentages. With a regular calculator, you can solve percentage questions in seconds once you understand a few formulas.

Percentage basics in plain English

A percentage means “out of 100.” So:

• 10% means 10 out of 100 (or 0.10)
• 25% means 25 out of 100 (or 0.25)
• 150% means 150 out of 100 (or 1.50)

The most important conversion is this: percentage ÷ 100 = decimal. Once you have the decimal form, calculator work becomes easy.

The three formulas you will use most

1) Find a percentage of a number

Formula: (Percentage ÷ 100) × Number

Example: What is 20% of 350?

20 ÷ 100 = 0.20, then 0.20 × 350 = 70.

2) Find what percent one number is of another

Formula: (Part ÷ Whole) × 100

Example: 18 is what percent of 24?

18 ÷ 24 = 0.75, then 0.75 × 100 = 75%.

3) Find percentage increase/decrease

Formula: ((New − Old) ÷ Old) × 100

Example: Price goes from 50 to 65:

(65 − 50) ÷ 50 = 0.30, then 0.30 × 100 = 30% increase.

How to use a calculator to find percentage step-by-step

Method A: Calculator without a % key

This method works on every phone and basic calculator.

1. Type the percentage number.
2. Press ÷ 100.
3. Press × and type the target number.
4. Press = to get the result.

Example: 12% of 450 → 12 ÷ 100 × 450 = 54.

Method B: Calculator with a % key

Some calculators let you type percentage directly. The exact behavior can vary by model, but a common sequence is:

1. Type the number (e.g., 450)
2. Press ×
3. Type the percent (e.g., 12)
4. Press % then =

If your result looks strange, use Method A. It is universal and always reliable.

Real-life examples

Discount shopping

You see 35% off a $80 item.

• Discount amount = 35% of 80 = 28
• Final price = 80 − 28 = 52

Restaurant tip

Bill is $64, and you want to leave 18%.

• Tip = 18% of 64 = 11.52
• Total = 64 + 11.52 = 75.52

Test scores

You scored 42 out of 50.

• (42 ÷ 50) × 100 = 84%

Salary raise

Salary rises from $48,000 to $52,800.

• Change = 52,800 − 48,000 = 4,800
• (4,800 ÷ 48,000) × 100 = 10% increase

Common percentage mistakes to avoid

• Forgetting to divide by 100: 25% is 0.25, not 25.
• Mixing “of” and “is what percent of”: These are different formulas.
• Using the wrong base number: In percent change, divide by the original (old) value.
• Rounding too early: Keep extra decimal places until the final step.

Quick mental shortcuts

Even without a calculator, these tricks help:

• 10% = move decimal one place left (10% of 250 is 25)
• 5% = half of 10%
• 1% = divide by 100
• 25% = one quarter
• 50% = half

Practice problems

Try these and verify with the calculator above:

1. What is 8% of 375?
2. 72 is what percent of 90?
3. A value drops from 240 to 180. What is the percent decrease?
4. Find the final price of a $120 item after a 15% discount.

Answers: 30, 80%, 25% decrease, and $102.

Final takeaway

If you remember just one thing, remember this: percentages become easy when you convert them to decimals first. Use the formulas in this guide, check your steps, and practice with real-world examples like discounts, tips, and score calculations. After a few tries, percentage math will feel automatic.