Free online calculator · Math
Percentage Calculator
Find a percentage of a number, calculate percentage increases and decreases, and compare values.
Formula • Worked example • Interpretation
Percentage of a number and percentage change
Percentages express parts per hundred. The same word “percent” is used for several different calculations, so first identify whether you need a portion or a change.
Calculation method
x% of y = (x ÷ 100) × y. Percentage change = ((new − old) ÷ |old|) × 100, provided the starting amount is not zero.
Worked example
15% of 80 equals 12. An increase from 80 to 100 is (100 − 80) ÷ 80 × 100 = 25%.
What your result means
A 20% discount followed by a 20% increase does not restore the original price: $100 becomes $80, then $96.
Tips for better calculations
Use the discount and sales-tax calculators when you need final prices after multiple percentage adjustments.
Assumptions and limitations
Percentage change is undefined for a zero baseline; negative baselines need careful interpretation. A percentage-point change is not the same as a percent change.
SiCalcs tools provide estimates and educational calculations; they do not replace professional financial, medical, tax, or legal advice.