“Twenty percent” can mean a fraction of an amount, a share of a total, or a change between two values. The Percentage Calculator separates these questions into three modes. Choosing the mode before entering numbers prevents an accurate formula from answering the wrong question.
Match the labels to the question
Enter the two numbers in First value (X) and Second value (Y). In Calculation, select X% of Y, X is what % of Y, or Percentage change from X to Y, then choose Calculate. The inputs accept positive and negative values within the displayed numeric range.
For X% of Y, the formula is X × Y / 100. With X equal to 15 and Y equal to 240, the result is 36.00. This answers “what amount is 15 percent of 240?” It does not answer how much a value increased.
For X is what % of Y, the formula is X / Y × 100. Entering 36 and 240 returns 15.00%. Here Y is the reference total and cannot be zero. Reversing the inputs changes the question and therefore the result.
Work through a percentage change
To compare an original amount of 80 with a new amount of 100, enter X as 80, Y as 100, and select percentage change. The difference is 20. Dividing by the original magnitude, 80, gives 25.00%.
The implementation uses (Y − X) / abs(X) × 100. That absolute-value denominator matters for negative originals. A move from −100 to −80 produces 20.00% under this convention because the difference is positive 20 relative to an original magnitude of 100. State this convention when sharing signed-value comparisons, since other reporting systems may use a different definition. A zero original has no supported percentage-change denominator and is rejected.
Keep units and interpretation consistent
Use comparable units and time periods in both fields. Comparing a monthly number with an annual number produces arithmetic, but usually not the intended interpretation. A percentage point difference between rates is also a different measure from a percentage change in those rates.
Results are rounded to two decimals for display and processed in your browser without an account connection. They do not include fees, tax rules, or an interpretation of financial records. For a price reduction with explicit savings, use the Discount Calculator. For cost and selling-price comparisons, the Profit Margin Calculator distinguishes margin from markup using their different reference amounts.