Question 1

What is the difference between percent change and a percentage-point change?

Accepted Answer

Percent change is relative to the starting value: going from 37% to 40% is a change of (40-37)/37 × 100 ≈ 8.1%. A percentage-POINT change is a plain subtraction of the two percentages: 40 − 37 = 3 points. Both describe the same move; they answer different questions, and mixing them up is one of the most common percentage mistakes.

Question 2

Why does 10% off then 10% more not return the original price?

Accepted Answer

Because the second percentage is taken from a different, smaller base. $100 decreased by 10% is $90; $90 increased by 10% is $99, not $100 — the 10% increase is 10% of $90, not of the original $100. This is the same reason a 50% cut followed by a 50% raise leaves you at 75%, not 100%.

Question 3

How does the calculator avoid rounding errors?

Accepted Answer

Every value you type is parsed into an exact integer (millionths, never a binary float) and every division is computed as an exact fraction rounded half-up at the very end — the same discipline Ochre's invoice engine uses for money. The only exception is compound growth and CAGR, which need floating-point exponentiation for fractional powers; those results carry a visible disclosure line saying so.

Question 4

What is the Find-X tool for?

Accepted Answer

Most percent questions are really one of a handful of algebra forms with a different piece missing — "20% of what number is 10?" and "10 is what percent of 50?" are different questions with different unknowns. Find-X lists 14 common sentence forms so you pick the one that matches your question instead of rearranging the formula yourself.

A percentage calculator that shows its work.

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Arithmetic is the easy part.