> ## Documentation Index
> Fetch the complete documentation index at: https://docs.simplifi.work/llms.txt
> Use this file to discover all available pages before exploring further.
# Building and Using Cost Code formulas
### Building a cost centre code “formula”
Cost centre codes are not invented in this system—they must **match what exists in payroll**, so you configure a formula that constructs the code from known attributes.
* Use a **Room/Department payroll code** (where the person is working).
* Or use **Home room payroll code** (their “main” location, even if they sometimes work elsewhere).
* Optionally append a **Role code** (e.g., “MAT” + “10” where MAT = maternity ward and 10 = nurse role code).
* You can insert **fixed text separators** (e.g., “MAT/10”).
You can create **multiple rules** (e.g., several different formulas) and choose which one a provider uses.
### Step by step:
1. Press **New Cost Centre Code** and type in a name. You can press the **In Use** toggle to archive the cost centre code if you'd like it to not be available for use. Press Save Code
2. Construct your formula using the system options. If you'd like to add free text then enter the text in the box before pressing the plus on the right.
Here's an example formula for a Room\_PayRollCode.
You will then need to set up when to apply the code using the [Payroll Rules Engine](/payroll-rules-engine). For a tutorial on [how to make a new payroll rule in the engine, press here](/how-to-make-a-new-payroll-rule-in-the-engine)