Percentage Calculator
Five percentage questions, answered live — % of a number, what percent, percent change, increase and decrease.
Percentage problems all sound alike but need different formulas, which is exactly why they trip people up: "what is 15% of 80" is not the same calculation as "15 is what percent of 80", and percent change is different again. This calculator lays out the five everyday forms as separate one-line calculators — fill in the one that matches how your question is phrased, and the answer appears as you type.
It covers: what is X% of Y (discounts, tax, commissions), X is what percent of Y (test scores, market share), percent change from old to new (price changes, growth rates — correctly signed, so decreases show as negative), and increase/decrease a value by a percentage (raises, markdowns). Everything computes locally in your browser with no rounding surprises — results show up to four decimal places when they matter. For splitting a restaurant bill with a percentage tip, the dedicated tip calculator is faster; for percentage growth of savings over years, use the compound interest calculator.
How to use the Percentage Calculator
- Find the row that matches your question — each row is its own calculator.
- Type your numbers into the boxes; the result appears instantly at the end of the row.
- For percent change, enter the old value first and the new value second — a negative result means a decrease.
- Copy the result, or change any number to recalculate live.
Frequently asked questions
How do I calculate X% of a number?
Multiply the number by the percentage divided by 100: 15% of 80 = 80 × (15 ÷ 100) = 12. The first row does this — enter 15 and 80 and you'll see 12.
What's the difference between percent change and percentage points?
Percent change is relative: going from 10% to 15% is a 50% increase (5 ÷ 10). Percentage points are absolute: that same move is +5 percentage points. This calculator computes percent change; subtract the values yourself for points.
Why is percent change from 50 to 40 not the same as from 40 to 50?
Because the change is measured against the starting value. 50→40 is −20% (10 ÷ 50), but 40→50 is +25% (10 ÷ 40). The direction matters, which is why the calculator asks for old and new values explicitly.
How do I reverse a percentage — find the price before a discount?
Divide by (1 − discount). If something cost $60 after 25% off, the original was 60 ÷ 0.75 = $80. Using the "decreased by" row: enter candidate original values until the result matches, or do the division directly.
Does the calculator round the results?
Results display up to four decimal places and drop trailing zeros, so everyday answers look clean (12, not 12.0000) while precise ones keep their accuracy. All math is done at full floating-point precision before display.