How do I calculate a discount?

Use X% of Y to get the discount amount, then subtract it from the price. For a $80 item at 25% off, the discount is $20 and the price is $60.

How do I add a percentage, like tax or tip?

Use % change from X to Y in reverse, or simply compute X% of Y and add it. A 15% tip on $60 is $9, so pay $69.

Why is my percent change negative?

The value went down. A drop from 100 to 80 is −20%, calculated against the original 100.

What's the difference between percent and percentage points?

Going from 10% to 15% is a 5 percentage-point rise, but a 50% relative change. This calculator computes the relative change.

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Percentage calculator

Percentages trip people up because the same two numbers can answer three different questions: what is 15% of 200, what share of 200 is 30, and how much did 80 change to become 100. Pick the question, enter two numbers, and get the answer with the exact formula shown beside it. This covers discounts, tax, tips, grade shares, price increases, and the percentage-point versus percent-change distinction that catches so many people out.

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What do you need?

Your estimate

Results

Planning estimate

Result30

What was computed15% × 200 — X percent of Y

The math, plainly

How it works

01
Pick the mode first — the same two numbers mean different things in each mode.
02
X% of Y multiplies; X as a share of Y divides; percent change divides the difference by the starting value.
03
Percent change is negative when the value falls and uses the absolute starting value as its base.

Try a real scenario

Tip on a discount

Inputs15% of 200

Result30.

Percentage calculator

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Results

How it works

Tip on a discount

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