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We often talk about “functions” and “formulas” when we talk about Microsoft Excel. In fact, some people use them interchangeably. However, there are differences between the two. To help you understand and use what you need, we will explain how they differ.
What is a function in Excel?
A function in Microsoft Excel it is a predefined formula. Built behind the scenes of the application, the functions allow you to perform calculations, formatting and similar tasks without the need to know operators or programming languages.
You can use a function to do things like add numbers, count cells, and trim blanks. Examples of common functions in Excel include:
 SUM
 TELL
 AVERAGE
 TRUNC
 PRUNE
Functions appear in capital letters, are available for you to select and use, and can be inserted into formulas that you create.
Each function in Excel requires a specific syntax or composition. You can see this syntax when you insert a function to help you build the formula. For example, if you click the Insert Function (fx) icon on the left of the formula bar, you can search for a function to insert.
Near the bottom of the window that appears, you will see the required syntax for each function that you select from the list.
You might see some arguments in the syntax, like “value” or “number”, which basically tell the function how it should behave. While some functions can be used without arguments, others cannot. For example, you can’t just use the SUM function by itself. It must be inserted into a formula that contains arguments enclosed in parentheses.
In some cases, functions can be used without arguments. For example, to enter the current date and time in a cell, you can use, NOW()
What is it a basic function . As you can see, there are no arguments, but the parentheses accompany the function as part of the syntax.
What is a formula in Excel?
A formula in Excel is an expression, like an equation, that you create within a cell. You can insert a function into your formula or create an equation without one.
Formulas must begin with an equal sign when inserted into a cell and are the final expressions used to perform the calculations or tasks that you configure. Once you add a formula to a cell, you will see it displayed in the formula bar at the top of your sheet.
Formulas with functions
If you select a function that you want to use, add it to the formula and then include the arguments that can include cell references, numbers, or text values. Examples of simple formulas that use functions in Excel include:

=SUM(A1:A10)

=COUNT(A1:A10)

=AVERAGE(A1:A10)

=TRUNC(7.5,1)

=TRIM(A1)
As you can see, each formula starts with a function. The parts of the formula in parentheses are the arguments. For example, if you insert the SUM
function in your formula, you must include what you want to add, such as a range of cells containing values.
Formulas without functions
Formulas can be used alone, without functions. You can then perform tasks like adding numbers and multiply values in cells . Examples of basic formulas without functions in Excel include:

=A1+A2

=C1C2

=2*4

=B1/B2

=D1*D2
Remembering the difference between functions and formulas
Although a function is technically a formula, it is a predefined formula, not one that you create. Therefore, the easiest way to tell the difference between a function and a formula in Excel is that you can insert a function in a formula that I know creates.
 Function – Predefined by Excel and can be inserted into a formula.
 Formula – Defined by you and can be used with or without a function.
For additional help, take a look at some lessons on Howto Geek School starting with why you need formulas and functions in Excel.