Percentage Calculator

How to use this percentage calculator

Pick what you want to figure out from the dropdown, then type your two numbers — the answer updates as you go. Choose "What is X% of Y" to take a percentage of a number (like a 15% tip on a $200 bill). Choose "X is what % of Y" to find what share one number is of another (like a score of 30 out of 200). Choose "Percent change from X to Y" to measure how much a value rose or fell from a starting point to an ending point.

How this is calculated

Each mode uses one simple formula:

• Percent of a number: result = (X ÷ 100) × Y. So 15% of 200 is (15 ÷ 100) × 200 = 30.
• What percent X is of Y: result = (X ÷ Y) × 100. So 30 out of 200 is (30 ÷ 200) × 100 = 15%.
• Percent change: result = ((Y − X) ÷ X) × 100. From 100 to 150 that's ((150 − 100) ÷ 100) × 100 = 50%. A negative answer means a decrease.

Worked examples

Percent of a number. Your restaurant bill is $200 and you want to leave a 15% tip. Set the mode to "What is X% of Y," enter 15 and 200, and you get 30 — so the tip is $30 and the total is $230. The same math works for sales tax, commission, or any "percent of" question.

What percent of. You answered 30 questions correctly out of 200 on a practice test. Switch to "X is what % of Y," enter 30 and 200, and the answer is 15%. This is the everyday way to turn a fraction or a part-of-a-whole into a percentage you can compare.

Percent change. A subscription went from $100 to $150. Use "Percent change from X to Y," enter 100 and 150, and you get 50% — a 50% increase. If the price had dropped from 150 to 100 instead, you'd see roughly −33.3%, a decrease. Increases and decrease are not symmetric, which is why a 50% rise needs only a 33% fall to undo it.

Quick tips

• Add a percentage to a number by finding the percent of it and adding it on. To add 15% to 200: 15% of 200 is 30, so 200 + 30 = 230. You can also multiply by 1.15.
• Subtract a percentage the same way, or multiply by (1 − the rate). Taking 20% off 50 means 50 × 0.80 = 40. For shopping math, our discount calculator does this in one step.
• Reverse a percentage by dividing. If a price already includes 20% and is $120, the original is $120 ÷ 1.20 = $100.

Common mistakes to avoid

• Mixing up part and whole. For "what percent," the number you're measuring goes first (the part) and the total goes second (the whole).
• Using the wrong base for percent change. Percent change is always measured against the starting value, not the ending one.
• Stacking percentages. Two 10% increases in a row total about 21%, not 20%, because the second builds on the new, larger number.

These are estimates for everyday math and education. For shopping savings, try our discount calculator.