Percentage Calculator

About this calculator

A free percentage calculator that handles the three questions people actually search for: "what is X% of Y", "what is the percent change from A to B", and "A is what percent of B". Pick an operation, type two numbers, and the result updates instantly, rounded to two decimal places. Everything runs in your browser; nothing you enter is uploaded or stored. The math is deliberately transparent — percent of a number multiplies a/100 by the number, percent change divides the difference by the starting value, and the what-percent mode divides the part by the whole. Division by zero returns 0 instead of an error, so the tool stays usable while you are still typing.

The three operations this tool covers

Almost every percentage question reduces to one of three shapes, and this calculator handles each as its own mode. "What is X% of Y" multiplies a rate by a base — it multiplies a divided by 100 by the number, so 15% of 200 is 15 ÷ 100 × 200 = 30. "Percent change from A to B" divides the difference between two values by the starting value. And "A is what percent of B" divides a part by a whole.

Pick the operation that matches the question you are asking, type the two numbers, and the result updates instantly, rounded to two decimal places. The math is deliberately transparent so you can check it by hand — there is no hidden rounding or weighting between the modes.

Where each mode shows up in real life

Percent of a number is the math behind a tip, a sales-tax line, a discount, or a sales commission — you know the rate and the total and want the slice. Percent change is how price moves, salary bumps, and traffic swings are reported, where the sign of the answer tells you whether the value rose or fell. The what-percent mode answers proportion questions: a score out of a possible total, or one line item as a share of a budget.

Choosing the right mode matters because they are not interchangeable. The percent change from 120 to 150 is 25%, but the reverse move from 150 back to 120 is a 20% decrease, not 25% — each is measured against its own starting value, which is exactly what the percent-change mode handles for you.

How division by zero is handled

Two of the modes divide by a number you supply: percent change needs a non-zero starting value, and the what-percent mode needs a non-zero whole. Rather than throw an error or show infinity when that denominator is zero, the calculator returns 0.

That choice keeps the tool usable while you are still typing — an empty or zero field simply reads as 0 until you enter a real value, instead of flashing an error message at every keystroke. Once both numbers are present the result is exact to two decimal places.

By variant

• Percent of a Number
• Percent Change

Questions

Is the percentage calculator free?

Yes. It is free, needs no account, and calculates entirely in your browser — none of the numbers you enter are uploaded or stored.

How do I find what percent of a number something is?

Use the "Percent of a number" operation and enter the percent first and the number second. For example, 15% of 200 is calculated as 15 ÷ 100 × 200 = 30.

How is percent change calculated?

Percent change is the difference between the new and original values divided by the original value, times 100. Going from 120 to 150 is (150 − 120) ÷ 120 × 100 = 25% increase; a smaller new value gives a negative percent change.

What happens if I divide by zero?

The calculator returns 0 instead of an error or infinity. Percent change needs a non-zero starting value and the what-percent mode needs a non-zero whole, so a zero in those slots produces 0 until you enter a real value.