How to Calculate Percentage: The Simple Math Trick Everyone Should Know

Last updated: May 2026 · 8 min read

I froze.

My friend looked at me and asked, "David, what is 15 percent of 200?"

Nothing.

My brain just stopped working. I knew I had learned this in primary school. But standing there, under pressure, I could not do the math in my head.

My friend laughed. I laughed too. But inside, I felt stupid.

That day, I decided I would never freeze again. I learned the trick. And now, I want to share it with you.

Here is the truth. You use percentages almost every day. Shopping discounts. Bank interest. Tax calculations. Tips at restaurants. Exam scores. Salary increases.

If you cannot calculate percentages quickly, you are at a disadvantage.

I will fix that for you right now. No complicated formulas. No fancy terminology. Just simple math that anyone can learn in five minutes.

– The One Trick That Makes Percentages Easy

Here is the trick that changed everything for me.

To find a percentage of any number, multiply the number by the percentage, then divide by 100.

That sounds complicated. Watch how simple it becomes.

Example one: 10% of 200

Multiply 200 by 10 = 2000

Divide 2000 by 100 = 20

10% of 200 is 20.

Example two: 15% of 200

Multiply 200 by 15 = 3000

Divide 3000 by 100 = 30

15% of 200 is 30.

Example three: 25% of 80

Multiply 80 by 25 = 2000

Divide 2000 by 100 = 20

25% of 80 is 20.

See the pattern? Multiply first. Then divide by 100.

That is the whole trick. Nothing else.

I use this almost every week. Shopping. Budgeting. Investing. It never fails.

If you want to learn more about using math in your personal finances, read our Low Income Budget Example article.

– How to Calculate Percentage Increase

This comes up all the time.

Your rent goes up. Your salary increases. A stock price rises. How much did it increase in percentage terms?

Here is the formula.

Step one: Find the difference between the new number and the old number.

Step two: Divide the difference by the old number.

Step three: Multiply by 100.

Your rent increased from ₦100,000 to ₦120,000.

Difference = 120,000 - 100,000 = 20,000

Divide by old number = 20,000 ÷ 100,000 = 0.2

Multiply by 100 = 20%

Your rent increased by 20%.

A stock price increased from $50 to $75.

Difference = 75 - 50 = 25

Divide by old number = 25 ÷ 50 = 0.5

Multiply by 100 = 50%

The stock increased by 50%.

That is percentage increase. Simple.

If you are saving for a goal, understanding percentage increases helps you track your progress. How to Save $1,000 Fast on a Low Income Without a Side Hustle uses percentages to show how small consistent savings add up.

– How to Calculate Percentage of a Total

Here is another common situation.

You have a total amount. You have a part of that total. What percentage is the part of the total?

Formula:

Divide the part by the total.

Multiply by 100.

You scored 45 marks out of 60 on a test.

Divide 45 by 60 = 0.75

Multiply by 100 = 75%

You scored 75%.

You spent ₦30,000 on food out of a ₦150,000 monthly budget.

Divide 30,000 by 150,000 = 0.2

Multiply by 100 = 20%

Food is 20% of your budget.

This is how you analyze your spending. Our Low Income Budget Example breaks down a full budget using percentage allocations.

– Real Life Examples You Will Actually Use

Here are situations where percentage math will save you.

Shopping sale: 25% off a ₦80,000 phone

25% of 80,000 = 80,000 × 0.25 = ₦20,000 discount

Final price = 80,000 - 20,000 = ₦60,000

Bank interest: 5% annual interest on ₦500,000 savings

5% of 500,000 = 500,000 × 0.05 = ₦25,000 interest per year

Salary increase: Your salary goes from ₦150,000 to ₦180,000

Increase = 30,000

Percentage increase = 30,000 ÷ 150,000 × 100 = 20%

Test score: You got 42 out of 50

Percentage = 42 ÷ 50 × 100 = 84%

Restaurant tip: You want to leave 10% on a ₦12,000 bill

10% of 12,000 = 12,000 × 0.10 = ₦1,200 tip

Sales tax: 7.5% VAT on a ₦50,000 item

7.5% of 50,000 = 50,000 × 0.075 = ₦3,750 tax

Total = 50,000 + 3,750 = ₦53,750

– Quick Reference Percentage Table

Keep this in your phone notes.

1% = divide by 100

5% = divide by 20

10% = divide by 10

15% = divide by 6.67 (or 10% + 5%)

20% = divide by 5

25% = divide by 4

30% = divide by 3.33 (or 10% × 3)

33% = divide by 3

50% = divide by 2

66% = multiply by 2 then divide by 3

75% = divide by 4 then multiply by 3

I have this saved on my phone. It helps me think faster when shopping.

– Final Thoughts

Percentages are not hard. You just need to practice.

Start with small numbers. Use the tricks I showed you. Test yourself in real situations. At the market. While shopping. When checking your bank account.

Soon, you will not freeze when someone asks you a percentage question. You will just answer.

And maybe, unlike me, you will never feel stupid in front of your friends again.

If you want to go deeper into personal finance math, explore these resources:

Math is your friend. Percentages are your tool. Use them well.