Percentage Calculator

How this percentage calculator works

Percentages show up in discounts, tips, grades, and growth rates — and they are easy to mix up. This page splits the three most common jobs: find X% of a number, find what percent one number is of another, and measure percent change from an old value to a new value.

The three modes

• Percent of: multiply Y by (X ÷ 100). Example: 15% of 80 = 12.
• Part vs whole: divide part by whole and multiply by 100. Example: 12 is 15% of 80.
• Change: (new − old) ÷ |old| × 100. Example: 80 → 100 is a 25% increase.

Percent vs percentage points

If an interest rate moves from 4% to 6%, that is a rise of 2 percentage points, but a 50% relative increase. Use the change mode for relative change; do not confuse it with a simple subtraction of percents when you mean points. Our guide on percent change vs percentage points walks through more examples from news and finance.

Worked examples

A $60 shirt at 30% off saves $18 (30% of 60), so you pay $42. A test score of 42 out of 50 is 84%. A portfolio that grows from $10,000 to $11,500 rose 15%.

Sales tax example: a $40 item with 7.5% tax adds 7.5% of 40 = $3.00, for a total of $43. Tip example: 18% of a $56 bill is $10.08; many people round to a convenient cash amount after the exact percent is known.

Discounts stacked in order

Two discounts applied one after another are not the same as adding the percents. Take 20% off, then 10% off the reduced price: you pay 80% × 90% = 72% of the original (a 28% total reduction), not 70%. Compute each step with “What is X% of Y?” using the updated base, or multiply the remaining factors.

How to use it

1. Pick the section that matches your question.
2. Enter the two inputs for that section.
3. Read the result; try alternate numbers to compare scenarios (for example, 10% vs 15% tip).
4. For finance headlines, decide whether you mean relative percent change or percentage points before you quote the number.

Scenario: raising a price without confusing customers

If a subscription moves from $20 to $25, percent change is +25%. Saying “it went up 5%” would be wrong; saying “it went up five dollars” is clear; saying “it went up 5 percentage points” would only make sense if you were talking about two percentages (for example, a tax rate), not dollar prices. Match the language to the quantity.

Frequently asked questions

How do I add a tip?

Use “What is X% of Y?” with the bill as Y and the tip rate as X, then add that result to the bill — or compute Y × (1 + X/100) in the basic calculator after you know the tip amount.

Why did percent change say “undefined”?

If the starting (“from”) value is zero, relative percent change is not defined. Describe the move in absolute terms instead.

Is a 20% decrease followed by a 20% increase back to the start?

No. 100 → 80 is −20%; 80 → 96 is +20%. You end below the start. Order and base matter.

How do I reverse a percent increase?

If a price rose 25% from an old value to $125, the old value is 125 ÷ 1.25 = $100. Dividing by (1 + rate) undoes a pure percent markup when no other fees applied.

Limitations

Division by zero (a zero “from” value in percent change) is undefined. Rounding may differ slightly from spreadsheet formatting. This page does not compute compound growth schedules — use the interest calculator when periods repeat.