Every calculator in this subsection answers some version of the same question — what is one number as a proportion of another, expressed out of 100 — but the exact phrasing of that question changes what the right calculation actually is, which is the real reason there are a dozen separate percentage calculators here rather than one general-purpose tool.
Calculators in this section
"What is 20% of 60", "what percentage of 60 is 12", and "60 rose to 72, what's the percentage increase" are three different calculations even though they all involve the same three numbers, and mixing them up is the single most common percentage mistake people make. Percentage change and percentage difference get confused just as often: a change moves from an original value to a new one and treats the order as meaningful (60 to 72 is a 20% increase, but 72 to 60 is a 16.7% decrease, not −20%), while a percentage difference between two values, with neither treated as the original, uses their average as the base instead.
The calculators here are grouped by which of these questions they answer rather than by difficulty, so the fastest way to use this subsection is to work out which sentence describes your problem before picking a calculator, not to hunt for the one with the biggest numbers.