The three most common percentage questions
Almost every percentage problem falls into one of three shapes: “what is X% of Y” (e.g. 15% of 80), “X is what percent of Y” (e.g. 20 is what % of 80), and “percent change between X and Y” (e.g. from 80 to 100 is what % increase). This calculator covers all three plus common variants like percent-off pricing and tip math.
Percent change: the sign matters
Percent change is (new value − old value) ÷ old value × 100. Going from 80 to 100 is a +25% increase, but going from 100 back down to 80 is a −20% decrease — the same absolute gap produces different percentages depending on which number is the base. This asymmetry trips people up constantly, and the calculator shows the formula alongside the answer so the logic is visible, not just the result.
Percent-off and discount math
For a 30% off $80 item: the discount is 30% of $80 ($24), so the final price is $80 − $24 = $56 — not simply “70 of something.” The calculator handles this directly so you get the sale price instantly without doing the subtraction by hand.
Why use UtilityApps for this
Instant results with no signup, and every answer shows the formula used — helpful if you’re learning the math, not just checking an answer.