Percentage Calculator

Five everyday percentage problems

Percentages appear in discounts, tip maths, exam scores, growth rates, and tax estimates. The wording changes (“what is 15% of…”, “what percent is…”, “percent change”) but each problem is a short formula. This page switches modes so you get the matching formula and a brief explanation with the result.

• What is X% of a number? — find a tip amount, discount amount, or portion of a total.
• X is what % of a number? — turn a score or share into a percentage of a whole.
• Percent change from A to B — measure increase or decrease relative to the starting value.
• Add / subtract X% — apply a markup or discount directly to a base amount.

Core formulas

• X% of N → N × X ÷ 100
• A is what % of B → A ÷ B × 100
• Percent change A→B → (B − A) ÷ A × 100
• Add X% → N × (1 + X÷100)
• Subtract X% → N × (1 − X÷100)

Worked examples

15% of 200 is 30. If a class scores 42 out of 50, that is 84%. A price rising from 80 to 100 is a 25% increase. Adding 20% to 50 gives 60; subtracting 20% from 50 gives 40 — note that −20% then +20% does not return to the original because percentages compound on the new base.

Percentage points versus percent change

If an interest rate moves from 4% to 5%, that is a rise of 1 percentage point, but a 25% relative increase (1÷4). This calculator’s percent-change mode answers the relative question. Finance pages such as Interest and Discount apply related ideas to money problems.

Common mistakes

• Dividing by the new value instead of the original when computing percent change.
• Adding percentage points as if they were the same as percent of a price.
• Stacking discounts incorrectly (20% off then another 20% off is not 40% off).

FAQs

Can the percent be more than 100?

Yes. Values over 100% mean more than the whole; negative percents mean a decrease in add/subtract modes.

Is this the same as VAT tax-inclusive maths?

Related, but VAT often needs tax-inclusive reverse calculations — see VAT / Sales Tax.

Full guide: Percentages, discounts, and VAT

Related: Discount, VAT / Sales Tax, Tip Calculator.