Excel BuiltIn Functions:
If you are looking for information on one of the builtin Excel functions, go to one of the following pages:
Excel Functions (ordered by category)See also:
The term 'Excel Formulas' can refer to any combination of Excel Operators and/or Excel Functions.
An Excel Formula is entered into a spreadsheet cell by typing in the = sign, followed by the required operators and/or functions. This may be as simple as a basic addition (e.g. "=A1+B1"), or it could be a complex combination of Excel Operators and multiple nested Excel Functions.
The links below provide examples of Excel Formulas, used to perform common tasks.
Calculating Percentages in Excel (Provides an overview, showing different types of percentage calculation)

Calculate a Percentage of a Number in Excel (E.g. how do I calculate 20% of 500?)

Calculate Percentage as a Proportion in Excel (E.g. what is 34 out of 40, expressed as a percentage?)

Calculate Percentage Change in Excel (E.g. if earnings increase from $20 to $25, what is the percentage increase?)

Calculate a Percentage Increase in Excel (E.g. what is the result if I increase 50 by 20%?)

Compound Interest Formula 
Excel Present Value Calculations 
Excel Future Value Calculations 
Age Calculation in Excel 
Calculate a Date Difference in Excel 
Calculate Time Difference in Excel 
Use Formulas to Convert a Time to a Decimal in Excel 
How to Convert Seconds to Time in Excel 
Excel String Concatenation 
Use Excel Formulas to Split a String in Excel 
For further examples of Excel formulas, see the Microsoft Office website.