Percentage Calculator

Percentage calculator for three common everyday calculations

Percentages show up constantly in daily life — in discounts, test scores, tax rates, salary increases, interest rates, and performance reports. This percentage calculator handles the three most common percentage questions in one place: finding a percentage of a number (for example, 15% of 250), finding what percent one value is of another (for example, 37 is what percent of 200), and calculating the percentage change between two values (for example, from 1,200 to 1,500). Each mode is designed to answer the specific question it names, not a generic calculation.

To use the calculator, select the mode that matches your question, enter the two values, and click Calculate. The labels on the input fields change based on the mode you choose, so you can see at a glance which number goes where. In "What is X% of Y?" mode, X is the percentage rate and Y is the base value you are applying it to. In "X is what percent of Y?" mode, X is the part and Y is the whole. In percent change mode, the first field is the original value and the second field is the new value after the change.

Percentages are often misread because the same numbers can mean different things in different contexts. A 20% discount on a 500 item saves you 100, but 20% of 500 items in a shipment means 100 units. Both are the same arithmetic, but the interpretation differs. This calculator shows the formula used alongside the result so you can confirm you are reading the answer correctly. Whether you are checking a price tag, grading assignments, comparing financial figures, or checking a claim someone made about growth, understanding which mode you need is as important as entering the right numbers.

Percent change is especially worth understanding precisely. It always measures relative to the starting value. If a price rises from 80 to 100, the percentage increase is (100 − 80) ÷ 80 × 100 = 25%. If that same price then falls back from 100 to 80, the percentage decrease is (100 − 80) ÷ 100 × 100 = 20%. The amount changed is the same (20), but the starting point is different each time, so the percentages are not the same. This asymmetry is one of the most common sources of confusion when people report or compare percentage changes.

Assumptions and how to use this calculator

• All values are treated as plain numbers. Enter percentages as simple numbers (type 15 for 15%, not 0.15).
• For "X is what percent of Y?" mode, the second value (Y) must be non-zero, since dividing by zero is undefined.
• For percent change mode, the formula is ((new value − original value) ÷ original value) × 100. The original value must be non-zero.
• Negative values are allowed in all modes, but interpret results carefully. Percent change involving negative baselines can produce counterintuitive signs.
• Results are rounded to two decimal places for readability. For very small values or precise financial work, treat the result as an approximation.

Common questions

How do I calculate a percentage of a number?

Select "What is X% of Y?", enter the percentage in the first box and the base number in the second box. The formula is straightforward: (X ÷ 100) × Y. For example, 15% of 250 equals (15 ÷ 100) × 250 = 37.5. This mode is commonly used for calculating discounts, tips, tax amounts, commission, and any situation where you are applying a percentage rate to a total.

How do I find what percentage one number is of another?

Choose "X is what percent of Y?" and put the part (the smaller or specific value) in the first field and the whole (the total or reference value) in the second field. The formula is (X ÷ Y) × 100. For example, 37 out of 200 equals (37 ÷ 200) × 100 = 18.5%. This mode is useful for grading (how many correct out of total), market share (how much of a total does one category represent), and budget comparisons (what fraction of total spending does one category use).

How is percent change calculated, and when does direction matter?

Percent change is calculated as ((new value − original value) ÷ original value) × 100. The sign of the result tells you the direction: positive means an increase and negative means a decrease. Direction matters because percent change is not symmetric. A 50% drop followed by a 50% rise does not return you to the original value. Starting at 100, a 50% drop gives 50, and a 50% rise from 50 gives 75, not 100. Always keep track of which value you are using as the baseline.

Can this calculator handle negative numbers and zero?

Negative numbers are accepted in all modes, and the math will run correctly. However, results involving negative inputs require more careful interpretation. For example, if the original value in percent change mode is negative, a larger (less negative) new value could still produce a negative percentage because of how the signs interact. If you are working with temperatures, debts, losses, or values that naturally go below zero, also look at the absolute difference alongside the percentage to make sure the result makes sense in your specific context.

When should I use percent change versus a simple percentage?

Use percent change when you have a "before and after" situation and you want to measure growth or decline relative to the starting point. This is common for price changes, sales comparisons, weight goals, and performance tracking over time. Use the "X is what percent of Y?" mode when you are comparing a part to a fixed whole at a single point in time, such as a score on a test or a category's share of a total. The key difference is whether one value is a starting point that changed (percent change) or a reference total that the part belongs to (part-of-whole percentage).