If you find yourself reaching for a calculator every time you need a discounted price or a month-over-month change, the new Percentage Calculator is for you. Switch between four modes with a single tab: B% of A, A is what % of B, % change from A to B, and A plus or minus B%.
Pick a mode, fill in two fields, and you get the result along with the formula. Edit a value and the result updates instantly. Press Enter (return on a Mac) to calculate and Esc to clear, and click any cell in the result table to highlight which value it is.