Percentage Calculator

Start with the value that is missing

To find 25% of 800, multiply 800 by 25 and divide by 100. The answer is 200. If the question is “200 is what percent of 800?”, the operation becomes 200 / 800 × 100, which gives 25%. The same numbers can require a different percentage formula because part, whole and rate have different roles.

Use “% of a Number” when the amount and rate are known. “What Percent” is for a known part and whole. If you are learning how to calculate percentage, labelling those two inputs before typing them is more reliable than choosing a formula from memory.

The “Add / Subtract %” mode starts with an amount. Adding 20% to 1,000 gives 1,200, while subtracting 20% leaves 800. A simple percentage calculator needs the original amount and the rate for a tip, discount or price adjustment.

A change rate always has a baseline

When an old and new value are known, use “Change Rate”. The calculation is (new - old) / old × 100. A percentage increase calculator returns 25% for a move from 80 to 100. Reversing those values produces a 20% decrease, not 25%, because 100 is now the baseline.

That is also why adding and then removing the same rate does not cancel out. Starting at 1,000, a 20% rise reaches 1,200; a 20% fall from 1,200 reaches 960. A percentage decrease calculator measures the fall against the amount that existed immediately before it.

Percentage points answer a different question

If a survey result moves from 40% to 60%, the gap is 20 percentage points. Relative growth is 50%: (60 - 40) / 40 × 100. Reports about grades, conversion rates and market share often become misleading when “percent” and “percentage points” are treated as interchangeable.

A zero starting value cannot produce a relative change rate because division by zero is undefined. For a negative start, this calculator divides by its magnitude. A move from -100 to -80 therefore reads as +20%. When a figure crosses zero, check the sign and absolute difference rather than relying on the percentage alone.

Reverse percentage requires division

A total of 1,200 after a 20% addition came from 1,200 / 1.20 = 1,000. Simply subtracting 20% from 1,200 would give 960. The first option under “Reverse” restores an amount before an added rate. The second finds the whole: if 120 is 15% of a number, 120 × 100 / 15 gives 800.

Use this percent calculator to compare amounts on the same basis. A discount applies to the original price, while a reverse calculation starts from the final amount. To calculate percentage changes across several periods, keep each period’s opening value as its own baseline.

The automatic percentage calculator displays the working formula, but it does not choose tax rates or grading weights. Take those from the bill or course rules. In English number format, 1,234 means twelve hundred and thirty-four; 1.234 is a decimal. Use 1,234.50 for a grouped decimal amount.

The main result is usually rounded to two decimal places; very small or large values use scientific notation. “Exact result” shows more digits, not unlimited precision: browser arithmetic and display rounding still apply. Copy Result includes the explanation; Copy beside Exact result takes only that value.