Percentages in Excel are just division plus the % number format. The key formulas are part/total and (new−old)/old.
Do it with AI insteadPercent of total
Use =part/total, e.g. =B2/$B$10, then apply the % format.
Percentage change
Use =(new-old)/old, e.g. =(C2-B2)/B2.
Format as percent
Select the cells and press Ctrl+Shift+%.
=(C2-B2)/B2The cell is in number format — apply the percent format instead of multiplying by 100.
Multiply the number by the percentage: =A2*20% returns 20% of the value in A2.
Use =A2*(1+B2) to increase and =A2*(1-B2) to decrease, where B2 holds the percentage.
Divide by 1 plus the percentage: =A2/(1+B2). For a price that includes 20% tax, =A2/1.2 gives the price before tax.