How to Calculate Percentages: 7 Everyday Methods with Examples

Percentages show up in shopping, cooking, exams, banking and news headlines, yet many people still reach for a calculator for the simplest ones. The good news is that almost every percentage question fits one of a handful of patterns. Learn these seven and you will be able to handle nearly anything you meet. You can check each answer with the Percentage Calculator.

1. Find a percentage of a number

Formula: result = (percent ÷ 100) × number.

What is 15% of 240? 0.15 × 240 = 36.

Mental shortcut: find 10% by moving the decimal point one place (24), find 5% by halving that (12), then add: 24 + 12 = 36.

2. Find what percent one number is of another

Formula: percent = (part ÷ whole) × 100.

You scored 45 out of 60. 45 ÷ 60 = 0.75, so the score is 75%.

3. Percentage increase or decrease

Formula: change % = ((new − old) ÷ old) × 100.

Rent rises from $800 to $900: (900 − 800) ÷ 800 = 0.125, an increase of 12.5%. A price that falls from $80 to $60 has changed by (60 − 80) ÷ 80 = −0.25, a decrease of 25%.

4. Discounts and sale prices

Formula: sale price = original × (1 − discount ÷ 100).

A $120 jacket at 25% off costs 120 × 0.75 = $90, saving $30. Add tax afterwards if it applies. Our Discount Calculator handles the tax step too.

Stacked discounts do not add up. Taking 20% off and then a further 10% off is not 30% off. It is 100 × 0.8 × 0.9 = 72, which is 28% off in total.

5. Finding the original price before a discount

If an item costs $90 after a 25% discount, divide by (1 − 0.25): 90 ÷ 0.75 = $120. Do not simply add 25% of $90 back, which would give the wrong answer of $112.50.

6. Tax, VAT and tips

Adding tax uses the same idea as a percentage increase: total = price × (1 + rate ÷ 100). An $80 item with 8.25% sales tax comes to 80 × 1.0825 = $86.60.

To remove tax from a tax-inclusive price, divide instead of subtracting: 86.60 ÷ 1.0825 = 80. The Sales Tax Calculator and VAT Calculator do this automatically, and our guide to sales tax, VAT and GST explains the differences.

For a tip, multiply the bill by the tip percentage, then split: an $86 bill with 18% tip is $15.48, or $101.48 in total. Between four people, that is $25.37 each. Use the Tip Calculator for quick splitting.

7. Percentage points versus percent

If an interest rate rises from 4% to 5%, it has gone up by 1 percentage point, but by 25 percent in relative terms (1 ÷ 4). News stories mix these up often, so always check which one is being described.

Common percentage mistakes

• Going up then down. A 25% rise followed by a 25% fall leaves you at 93.75% of the start, not 100%.
• Using the wrong base. Percentage change is always measured against the old value.
• Subtracting instead of dividing when removing tax from a total.
• Forgetting to convert. Divide the percent by 100 before multiplying (15% is 0.15).

Quick reference table

Practise

Try making up your own examples using prices you see when shopping, then check them with the calculator. After a few days the mental shortcuts will feel natural, and the formulas above will cover almost every percentage question you meet.