# Invoice expenses
Add extra costs — such as travel, materials, or service fees — to projects as expenses, then bill them. The relevant **expense type** must first be created in Aerion.

:::lock{title="Required rights"}
Project management
:::

## Overview

The expenses overview sits at the bottom of the Invoices tab on both projects and sub-projects. It's split into billable, billed, and non-billable expenses.

![](/images/guides/invoice-expenses/image-mqqndb3i.png)

## Create an expense

Click the **+** icon to create a new expense. Depending on the type — **amount-based** or **percentage-based** — different options apply.

### Amount-based expenses

![](/images/guides/invoice-expenses/image-mqqnfkp1.png)

Amount-based expenses have either a fixed price (e.g. a workshop) or a fixed price per unit (e.g. mileage), with these options:

* **Date** — when the expense occurred (omitted when **Recurring** is enabled).
* **Note** — comments or notes on the expense.
* **Billable** — whether the expense is billable and available to select at invoicing.
* **Included in budget** — whether the expense is part of the project budget or increases the budget when billed. Available only for projects with a fixed budget.
* **Recurring** — whether the expense is billed once or recurring. Recurring expenses can be added to the invoice again at every invoicing.
* **Internal cost** — the internal cost of the expense.
* **Billable amount** — the amount billed to the client.
* **Receipt** — upload a receipt.

### Percentage-based expenses

![](/images/guides/invoice-expenses/image-mqqnk4oq.png)

Percentage-based expenses add a percentage on top of an invoice's amount, with these options:

* **Date** — when the expense occurred (omitted when **Recurring** is enabled).
* **Note** — comments or notes on the expense.
* **Included in budget** — whether the expense is part of the project budget or increases the budget when billed. Available only for projects with a fixed budget.
* **Recurring** — whether the expense is billed once or recurring. Recurring expenses can be added to the invoice again at every invoicing.

## Bill expenses

![](/images/guides/invoice-expenses/image-mqqnl9af.png)

When you [create an invoice](/guides/invoice-projects), all billable expenses are shown and can be added to the invoice as extra line items.

The total of all selected expenses is summarized in a single **Expenses** line item. Recurring expenses are available again at every invoicing.