Custom functions in Google Sheets - Step-by-Step Guide

Introduction

Custom functions let you create your own formulas in Google Sheets. They help you do special calculations or tasks that built-in formulas can't do. This is useful when you want to automate or simplify repeated work.

When you want to calculate a special value that Google Sheets does not have a formula for.

When you need to reuse a complex calculation many times without typing it over and over.

When you want to connect your sheet to external data or services using simple formulas.

When you want to create a formula that takes inputs and returns a custom result.

When you want to make your spreadsheet easier to understand by naming your own formulas.

Steps

Step 1: Open

- Google Sheets document

Your spreadsheet is ready to use and edit

Step 2: Click

- Extensions menu, then select Apps Script

The Apps Script editor opens in a new tab

Step 3: Delete any existing code and type

- Apps Script editor code window

You have a blank script to write your custom function

💡 Start your function with the word function and give it a name without spaces

Step 4: Write a function like: function MYFUNCTION(input) { return input * 2; }

- Apps Script editor code window

Your custom function doubles the input number

Step 5: Click

- Save icon or File > Save

Your script is saved and ready to use

Step 6: Go back to your Google Sheet and type

- Any cell

The custom function runs and shows the result

💡 Use =MYFUNCTION(5) to get 10 as output

Before vs After

Before

Sheet has no formula to double a number easily

After

Typing =MYFUNCTION(5) in a cell shows 10 as the result

Settings Reference

Script editor

📍 Extensions > Apps Script

Create and manage your custom functions

Default: Blank script

Function name

📍 In the Apps Script code

Identify your custom function to use in the sheet

Default: None

Return value

📍 Inside your custom function code

Send the result back to the cell where the function is used

Default: None

Common Mistakes

Naming the function with spaces or special characters

Google Sheets requires function names without spaces or special symbols

Use simple names like MYFUNCTION or DoubleValue

Not returning a value from the function

Without a return statement, the function shows no result in the sheet

Always use return to send the result back, e.g., return input * 2;

Trying to use custom functions that call services requiring authorization

Custom functions cannot run services that need user permission

Keep custom functions simple and avoid calls to restricted services

Summary

Custom functions let you create your own formulas in Google Sheets using Apps Script.

You write the function in the Extensions > Apps Script editor and save it.

Use the function in your sheet by typing =FunctionName(arguments).

Function names must be simple and the function must return a value.

Custom functions cannot use services that need special permissions.