Find Percentage

May 4, 2026

You spot a 30% off sale and need to know the final price. A test score reads 17 out of 20 – what is that as a percentage? These situations all come down to one skill: find percentage. This guide breaks down the three most common percentage problems and shows you how to solve them with straightforward formulas and worked examples.

How Do You Find a Percentage of a Number?

To find a percentage of a number, multiply the base number by the percentage expressed as a decimal or fraction.

Formula:
Part = (Percent / 100) × Whole

Example: Find 12% of 200.
12% as a decimal is 0.12.
Part = 0.12 × 200 = 24.
So 12% of 200 is 24.

You can also write it as a fraction: (12/100) × 200 = (12×200)/100 = 2400/100 = 24.

This method works for any “find percentage of a number” problem – discounts, tips, VAT, or interest.

The calculator above handles all three main percentage tasks: find a percent of a number, find what percent one number is of another, and find the percentage increase or decrease. Enter the values you know, and the missing one is computed instantly.

How to Find What Percent One Number Is of Another

Often you have two numbers and need to express one as a percentage of the other – for example, a score on a test.

Formula:
Percent = (Part / Whole) × 100

Example: 45 is what percent of 180?
Percent = (45 / 180) × 100 = 0.25 × 100 = 25%.
So 45 is 25% of 180.

Another real‑world use: a household budget of $3,200 includes $800 for rent. Rent as a percentage of the total: (800/3200)×100 = 25%.

How to Calculate Percentage Increase or Decrease

When a value changes from an old amount to a new amount, you can find the percentage change.

Formula:
Percent Change = ((New – Old) / Old) × 100

A positive result means an increase; a negative result means a decrease.

Example (increase): A phone bill rises from $60 to $75.
Percent change = ((75 – 60) / 60) × 100 = (15/60)×100 = 0.25×100 = 25% increase.

Example (decrease): A stock price drops from $140 to $105.
Percent change = ((105 – 140) / 140) × 100 = (–35/140)×100 = –0.25×100 = –25%.
The price fell by 25%.

This formula is used for salary raises, population changes, inflation, and sales performance.

How to Find the Original Amount Before a Percentage Change

If you know the final amount after a percentage increase or decrease, you can work backward to the original.

After a percentage increase:
Original = Final / (1 + Percent/100)

After a percentage decrease (discount):
Original = Final / (1 – Percent/100)

Example: A sofa on sale has a 20% discount, and the sale price is $480. Original = 480 / (1 – 0.20) = 480 / 0.80 = $600.

Example: After a 15% service charge, the total restaurant bill is $69. Original = 69 / (1 + 0.15) = 69 / 1.15 = $60.

Quick Mental Math Tricks for Finding Percentages

10% – move the decimal point one place left.
10% of 340 = 34.
5% – half of 10%.
5% of 340 = 34 / 2 = 17.
1% – move the decimal two places left.
1% of 340 = 3.4.
50% – divide by 2.
25% – divide by 4.
20% – divide by 5.

Combine these for more complex percentages: 15% = 10% + 5%, 30% = 10% × 3. These shortcuts let you find percentages without a calculator in everyday situations.

Frequently Asked Questions

How do I find 20% of 150?

Multiply 150 by 0.20. 150 × 0.20 = 30. So 20% of 150 is 30. Alternatively, multiply 150 by 20 and divide by 100: (150×20)/100 = 3000/100 = 30.

How do I find what percent 25 is of 200?

Divide 25 by 200 and multiply by 100: (25/200)×100 = 0.125×100 = 12.5%. So 25 is 12.5% of 200.

What is the percentage increase from 50 to 75?

Subtract the old value from the new value: 75 – 50 = 25. Then divide the difference by the old value: 25/50 = 0.5. Multiply by 100: 0.5×100 = 50% increase.

Can I find a percentage without a calculator?

Yes. Use simple fraction equivalents: 10% is one tenth, so divide by 10; 25% is one quarter, divide by 4; 50% is half, divide by 2. Chain these to handle other percentages.

What is the formula for finding a percentage of a number?

The formula is (percentage / 100) × total number. For 15% of 300, calculate (15/100)×300 = 0.15×300 = 45.

How do I find the original number before a percentage was added?

If the final number includes a P% addition, divide by (1 + P/100). Example: after 20% addition, final is 120; original = 120 / 1.20 = 100. For a discount, divide by (1 – discount%/100).