1) Check whether the formula refers, directly or indirectly, to a reference that includes the formula itself.

2) Make sure that none of the references in the formula form a loop.

3) If necessary, assign a value to the cell containing the formula.

4) If the formula refers to other worksheets, make sure that the referenced sheets exist and contain the data you want them to. If they do not, adjust the formulas accordingly.

5) If the formula contains an error code (e.g. #VALUE!), check the expression that produces the error code. Alter the expression so that it returns the value you expect.