The basic formula for calculating percentage in Excel is (Part/Total)*100. To display the result as a percentage, you can either multiply by 100 and format as a number, or format the cell as percentage (which automatically interprets decimals as percentages).
For example, if you have a value of 25 in cell A1 and a total of 100 in cell B1, you would write =A1/B1 and then format the cell as percentage, or write =(A1/B1)*100 and leave it as a number format. The percentage format approach is cleaner—just enter the formula =A1/B1, then use the Home tab > Number Format dropdown and select "Percentage."
To calculate percentage change between two values, use =(New Value - Old Value)/Old Value*100 or =((B1-A1)/A1) with percentage formatting.
For finding what percentage one number is of another (e.g., "What % is 30 of 200?"), use =30/200 formatted as percentage, which shows 15%.
You can also use the PERCENTAGE function in some spreadsheet contexts, though this varies by version. Most users rely on the division formula with percentage cell formatting, which is straightforward and works consistently across all Excel versions.