how to work out percentages on a calculator

Percentages are everywhere: sale prices, exam grades, tax, interest rates, tips, and investment returns. The good news is that once you understand a few simple button sequences, percentage calculations become fast and easy.

What a percentage actually means

A percentage is just a number out of 100. So:

• 10% means 10 out of 100
• 50% means 50 out of 100 (which is one-half)
• 125% means 125 out of 100 (or 1.25 times)

When using a calculator, it helps to remember this conversion:

percentage ÷ 100 = decimal

Example: 18% = 0.18

The 5 most useful percentage calculations

1) Find a percentage of a number

Question: What is 20% of 80?

Formula: (20 ÷ 100) × 80 = 16

Calculator sequence: 20 ÷ 100 × 80 =

2) Find what percent one number is of another

Question: 15 is what percent of 60?

Formula: (15 ÷ 60) × 100 = 25%

Calculator sequence: 15 ÷ 60 × 100 =

3) Find percentage increase or decrease

Question: Price changed from 50 to 65. What is the percentage change?

Formula: ((65 - 50) ÷ 50) × 100 = 30%

If the result is positive, it is an increase. If negative, it is a decrease.

4) Add a percentage to a number

Question: Add 12% to 200.

Method: 200 × (1 + 12/100) = 224

Calculator sequence: 200 × 1.12 =

5) Subtract a percentage from a number

Question: Take 30% off 90.

Method: 90 × (1 - 30/100) = 63

Calculator sequence: 90 × 0.70 =

How to use the % key (if your calculator has one)

Different calculators handle the percent key differently, but most standard and phone calculators follow similar behavior in basic shopping math.

• Discount: 90 - 30% = often returns 63
• Tax/tip add-on: 200 + 12% = often returns 224

If your calculator gives unexpected results, use the universal decimal method shown above. It works on every calculator.

Common real-life examples

Sales discount

A jacket costs $120 and is 25% off.

• Discount amount: 25% of 120 = 30
• Sale price: 120 - 30 = $90

Restaurant tip

Your bill is $48 and you want to tip 18%.

• Tip: 48 × 0.18 = 8.64
• Total: 48 + 8.64 = $56.64

Exam score

You scored 42 out of 50. What percentage is that?

• 42 ÷ 50 × 100 = 84%

Pay raise

Your salary rises from 40,000 to 46,000.

• Increase = 6,000
• 6,000 ÷ 40,000 × 100 = 15% increase

Quick mistakes to avoid

• Forgetting to divide the percent by 100
• Using the new value instead of the original value when finding percent change
• Mixing up “percent of” and “percent change”
• Rounding too early (round at the final step when possible)

Practice problems

Try these in your calculator, then check the answers:

1. What is 35% of 240?
2. 18 is what percent of 72?
3. A value moves from 80 to 68. What is the percentage change?
4. Increase 150 by 8%
5. Decrease 500 by 12%

Answers: 84, 25%, -15% (15% decrease), 162, 440.

Final takeaway

If you remember only one rule, remember this: percent means “divide by 100.” Once you convert percentages into decimals, calculator steps become straightforward and reliable every time.