How to Calculate Percentages?

At a glance

What it does and when to use it

A percentage calculator solves part-of-whole, relative share, and change between values.

Use it for discounts, price changes, grades, taxes, and everyday comparisons.

What to enter

Enter the percentage and amount, or two values, depending on the question.

How to read the result

Identify the base value; the same difference can represent different percentages.

Percentages look simple, but people often mix up the three common question types: a percent of an amount, a part as a percent of the whole, and percentage change between an old value and a new value.

The easiest way to handle percentages: identify the base, do the calculation, then check the result.

1. What is X% of Y?

Question: What is 20% of $500?

Step 1

20 ÷ 100 = 0.2

Final calculation

0.2 × 500 = 100

Result

20% of $500 = $100

Quick method: divide the percentage by 100 first, then multiply by the amount.

2. X is what percent of Y?

Question: What percent of $400 is $80?

Step 1

80 ÷ 400 = 0.2

Final calculation

0.2 × 100 = 20%

Result

$80 is 20% of $400

Order matters here: divide the part by the whole first, and only then convert to a percent.

3. How do you calculate percentage change?

Question: A price increased from $100 to $120. What is the percentage change?

Step 1

120 − 100 = 20

Step 2

20 ÷ 100 = 0.2

Final calculation

0.2 × 100 = 20%

Result

The percentage change is 20%

For percentage change, always divide by the old value, not the new one.

Real-world examples

Store discount: $200 item, 15% off → save $30, pay $170
Sales tax: $1,000 + 8% tax = $1,080
Interest: $10,000 at 6% a year = $600 interest per year

A common mistake to avoid

A 50% increase followed by a 50% decrease does not bring you back to the starting point. Starting at 100, going up to 150, then dropping by 50% takes you to 75, not back to 100.

→ Calculate percentages now

Common mistakes

Dividing by the new value instead of the original value for change.
Adding consecutive percentages as if they shared the same base.

Frequently asked questions

How do I calculate a discount?

Multiply price by the discount rate, then subtract that amount.

Do equal increases and decreases cancel out?

No, because the second change uses a different base.

How to Calculate Percentages?

At a glance

What it does and when to use it

A percentage calculator solves part-of-whole, relative share, and change between values.

Use it for discounts, price changes, grades, taxes, and everyday comparisons.

What to enter

Enter the percentage and amount, or two values, depending on the question.

How to read the result

Identify the base value; the same difference can represent different percentages.

Percentages look simple, but people often mix up the three common question types: a percent of an amount, a part as a percent of the whole, and percentage change between an old value and a new value.

The easiest way to handle percentages: identify the base, do the calculation, then check the result.

1. What is X% of Y?

Question: What is 20% of $500?

Step 1

20 ÷ 100 = 0.2

Final calculation

0.2 × 500 = 100

Result

20% of $500 = $100

Quick method: divide the percentage by 100 first, then multiply by the amount.

2. X is what percent of Y?

Question: What percent of $400 is $80?

Step 1

80 ÷ 400 = 0.2

Final calculation

0.2 × 100 = 20%

Result

$80 is 20% of $400

Order matters here: divide the part by the whole first, and only then convert to a percent.

3. How do you calculate percentage change?

Question: A price increased from $100 to $120. What is the percentage change?

Step 1

120 − 100 = 20

Step 2

20 ÷ 100 = 0.2

Final calculation

0.2 × 100 = 20%

Result

The percentage change is 20%

For percentage change, always divide by the old value, not the new one.

Real-world examples

Store discount: $200 item, 15% off → save $30, pay $170
Sales tax: $1,000 + 8% tax = $1,080
Interest: $10,000 at 6% a year = $600 interest per year

A common mistake to avoid

A 50% increase followed by a 50% decrease does not bring you back to the starting point. Starting at 100, going up to 150, then dropping by 50% takes you to 75, not back to 100.

→ Calculate percentages now

Common mistakes

Dividing by the new value instead of the original value for change.
Adding consecutive percentages as if they shared the same base.

Frequently asked questions

How do I calculate a discount?

Multiply price by the discount rate, then subtract that amount.

Do equal increases and decreases cancel out?

No, because the second change uses a different base.