Some common Excel formulas include SUM, which calculates the sum of values within a specified range of cells, COUNT, which counts the number of cells that have characters or numbers in them, and INT, which eliminates the fractional part of a number. Another common formula is NOW, which displays the system date and time.

Excel users can manually enter formulas or insert functions, which are simply built-in formulas. The Insert Function button is usually under the Formulas tab. There are various types of functions, such as financial functions, logical functions, math functions and statistical functions. An example of a math functions is AVERAGE, which calculates the average of values in a specified range of cells. Some functions are only available in recent versions of Microsoft Excel.

IF, COUNTIF, SUMIF, ROUND and TODAY are more examples of commonly used Excel functions. IF tests for a true or false condition and returns a value, depending on state of the condition. The SUMIF function calculates the sum of a range of cells that meet a certain criteria. The COUNTIF function counts the number of cells in a range that meet a specific criteria. The ROUND function rounds a number off to a specific number of decimal places. As opposed to the NOW function, the TODAY function returns only the system date.