Percentage Calculator

Percentages show up in retail discounts, tax brackets, tipping, statistics, and finance — and the three operations look similar but mean different things. The calculator covers all three: percentage of, percent change, and percent difference.

Three percentage formulas

Percentage of a number: (X / 100) × Y. So 20% of 80 = 0.20 × 80 = 16. Percent change: (new − old) / old × 100. From 50 to 75 is +50%, from 75 to 50 is −33%. Percent difference (symmetric): |a − b| / ((a + b) / 2) × 100. Use this when neither value is the baseline.

When to use this calculator

Use 'percentage of' for tips, sales tax, and discount calculations. Use 'percent change' for tracking growth — revenue, weight, anything with a clear before-and-after. Use 'percent difference' when comparing two measurements that don't have a 'first' (the diameter of two pipes, the height of two people).

Worked example

A laptop drops from $1,200 to $999. Percent change: (999 − 1,200) / 1,200 × 100 = −16.75%. Percent difference: |1,200 − 999| / ((1,200 + 999) / 2) × 100 = 18.3%. Different numbers, both correct — they answer different questions.

Limits and assumptions

Enter plain numbers: 25 means 25%, with no currency or unit handling. Percentage change divides by the absolute value of the starting number, so a move from −50 to 50 shows as +200%, and any division by zero returns 0 instead of an error. Results are displayed with up to four decimal places.

Each of the three calculations stands alone. The tool does not chain percentages, reverse one (find the price before a discount) or compound repeated changes, so a 10% rise followed by a 10% fall has to be worked as two steps.

Frequently asked questions