Percentage Calculator

Four percentage calculations in one tool

Percentages come up when you shop, tip, budget, mark exams, read a pay slip or compare numbers over time. This calculator handles the four questions people ask most, and it writes out the result in plain words so you can check that it answers the question you meant.

How to use it

1. Pick what you want to find from the menu.
2. Fill in the two boxes. The labels change to match the question.
3. Read the answer and the sentence beneath it. Copy it if you need it elsewhere.

The four modes and their formulas

1. What is X% of Y?

Result = Y × X ÷ 100. Example: 15% of 240 is 240 × 15 ÷ 100 = 36. This is the calculation behind tips, sales tax and commission.

2. X is what percent of Y?

Percent = X ÷ Y × 100. Example: if you answered 42 of 50 questions correctly, 42 ÷ 50 × 100 = 84%.

3. Percentage change from X to Y

Change = (Y − X) ÷ X × 100. A positive result is an increase and a negative one is a decrease. Example: a price moving from $50 to $60 is (60 − 50) ÷ 50 × 100 = a 20% increase. The change is always measured against the starting value, so a 20% rise followed by a 20% fall does not return you to where you began.

4. Price after a discount

Sale price = Original × (1 − Discount ÷ 100). Example: a $80 jacket at 25% off costs 80 × 0.75 = $60, so you save $20.

Common mistakes

• Mixing up percent and percentage points. Going from 4% to 5% is a rise of one percentage point but a 25% increase.
• Using the wrong base. A percentage is always “of” something. Change the base and the answer changes.
• Stacking discounts by adding them. Two successive 20% discounts take 36% off in total, not 40%, because the second is taken from the reduced price.

Frequently asked questions

How do I calculate a tip?

Use the first mode. For a $64 bill and an 18% tip, enter 18 and 64 to get $11.52.

How do I take a percentage off a price?

Use the discount mode to see both the new price and the amount saved.

Can I use decimals?

Yes. Values such as 7.5% or 0.25 work.