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Calculating Percentages with a Basic Calculator

Published on January 1, 2025

No % button? No problem.

Whether you're shopping for deals, figuring out tips at a restaurant, or converting school grades, percentages come up all the time. But what if your calculator doesn’t have a dedicated %key? Don’t worry—it’s easy to calculate percentages manually. In this guide, we’ll break it down step-by-step so you can do quick, accurate percentage calculations anytime, anywhere.

1. Finding Percentages Without a % Button

Most basic calculators don’t include a % function. Instead, use this simple formula:

X% of Y = (X ÷ 100) × Y

Let’s walk through a couple of real-life examples.

🔹 Example 1: What is 20% of 150?

  • Step 1: Divide the percentage by 100 → 20 ÷ 100 = 0.2

  • Step 2: Multiply that number by the total → 0.2 × 150 = 30

✅ Answer: 20% of 150 is 30.

🔹 Example 2: What is 7.5% of 85?

  • 7.5 ÷ 100 = 0.075

  • 0.075 × 85 = 6.375

✅ Answer: 7.5% of 85 is 6.375.

2. Converting Fractions to Percentages

Fractions and percentages are closely related—just different ways to express the same part of a whole.

Here’s how to convert a fraction into a percentage:

(Numerator ÷ Denominator) × 100 = Percentage

🔹 Example 1: Convert 3/4 to a percentage

  • 3 ÷ 4 = 0.75

  • 0.75 × 100 = 75

✅ Answer: 3/4 = 75%

🔹 Example 2: Convert 5/8 to a percentage

  • 5 ÷ 8 = 0.625

  • 0.625 × 100 = 62.5

✅ Answer: 5/8 = 62.5%

This is handy when interpreting grades, batting averages, or test scores.

3. Quick Percentage Calculations for Everyday Situations

💸 Tips at Restaurants

To calculate a tip, multiply your bill by the tip rate (usually 15%, 18%, or 20%).

Let’s say your bill is $46, and you want to leave an 18% tip:

  • 18 ÷ 100 = 0.18

  • 0.18 × 46 = 8.28

✅ Tip: $8.28
💡 Final bill: $46 + $8.28 = $54.28

🏷️ Discounts While Shopping

To figure out how much you’ll save on a discount, multiply the original price by the discount percentage.

🔹 Example 1: 30% off a $120 jacket

  • 30 ÷ 100 = 0.30

  • 0.30 × 120 = 36

✅ You save $36
💡 Final price: $120 - $36 = $84

🔹 Example 2: You’re offered 25% off, but want to know the final price directly.

Use this shortcut:

Final Price = Original Price × (1 - Discount Rate)

For 25% off:

  • 1 - 0.25 = 0.75

  • Original price × 0.75 = Final price

  • $200 × 0.75 = $150

✅ Answer: The jacket now costs $150

4. Bonus: Finding What Percentage One Number Is of Another

Sometimes you need to reverse the process—what percentage is A of B?

Use this formula:

(Part ÷ Whole) × 100 = Percentage

🔹 Example: What percentage is 45 out of 60?

  • 45 ÷ 60 = 0.75

  • 0.75 × 100 = 75

✅ Answer: 45 is 75% of 60

Final Thoughts

Calculating percentages might seem intimidating without a % button, but once you know the formulas, it becomes second nature. With a little practice, you’ll be able to:

  • Find percentages of any number

  • Convert fractions into percentages

  • Quickly figure out tips, discounts, and more

  • Work backward to determine percentage values

All it takes is basic multiplication and division—and your standard calculator can handle that with ease.

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