# Built-in Functions

## Introduction

This guide explains what built-in functions there are in Rulecube and how to use them.

Rulecube has many built-in functions ready to use for you and grouped them into these categories:

* Global
* Finance
* HTTP
* Mail
* MongoDB
* SQL
* Statistics
* Workflow
* System
* Array
* Date

For example, in the Finance group, you have the `pv` function for calculating the present value of a loan or investment. And in the Statistics group, you'll find the `mean` and `median` functions. 

To discover what's available, the best way is to click on the ![](/files/A38mSqTGAD1JPrMB1MdV) icon and then on "Documentation". This will open the Rulecube Manual.

Alternatively you can access this Manual from any code editor, like when editing a Rule:

<figure><img src="/files/rrjsxqFLutuuFzDxqoXG" alt=""><figcaption><p>Clicking the "Rulecube manual" link will open the Manual in a new window.</p></figcaption></figure>

## Procedure

Let's say you want to calculate the VAT amount from an amount that includes the VAT. The resulting VAT amount can have several decimal places, but for a neat presentation, you want to limit the decimal places to two. Rulecube has the `ROUND` function for this:

1. Create a ruleset named `VAT_calculator`.

2. Create an input named `AmountIncludingVAT` and set its **Type** to `number`.

3. Create a rule named `ExtractVAT` and set its **Type** to `number` and the **Expression** to:<br>

   <pre class="language-javascript" data-line-numbers><code class="lang-javascript">ROUND(AmountIncludingVAT / 121 * 21, 2)
   </code></pre>

4. Click **Save** and click **Try it out** to test the ruleset.

## Additional resources

* [Language (Methods) Reference](/language-reference.md)


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