Three percentage questions, three formulas
Percent of a number multiplies the base by the percentage divided by 100. Use it for a discount amount, tax estimate, commission, or share of a budget. What percent? divides the part by the whole and multiplies by 100. Use it for a grade, completion rate, conversion rate, or category share. Percentage change subtracts the starting value from the ending value, divides by the starting value, and multiplies by 100.
Worked examples
With 15 and 200 in the first panel, 15% of 200 is 30. With a part of 30 and a whole of 200, the second panel returns 15%. Moving from 80 to 100 is an increase of 20 relative to the original 80, so the third panel returns a 25% increase. If the ending value were 60 instead, the result would be negative, indicating a decrease.
How to choose the correct base
The denominator changes the meaning. “30 is what percent of 200?” uses 200 as the whole. “How much did 80 grow to reach 100?” uses 80 as the starting value. Reversing the two values produces a different percentage because percentage change is measured relative to the original amount, not the final amount.
Limits and zero values
The calculator accepts decimals and negative values, but interpret them in context. What-percent and percentage-change calculations cannot divide by zero; when the whole or starting value is zero, the page shows a dash rather than an invented percentage. Percentage points are also different from percent change: moving from 10% to 15% is a 5-point increase and a 50% relative increase.
Privacy behavior
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