It's nice to see you here in the Community, @brooke5.

There are two scenarios you can consider in adding a mark up on your invoices. Let me provide them to you and help you from there.

Just to clarify, which version of QuickBooks Desktop are you using? If you're using QuickBooks Enterprise, you can refer to the steps provided by my colleague @KhimG.

But if you're using another version of QuickBooks, you can create a new item for the markup and add it to your invoices. Note that you'll need to manually calculate for the markup price and edit it on the invoice.

To create a new item, you can follow the steps below:

1. Click on List from the menu bar.
2. Choose Item List.
3. From the Item drop-down, click on New.
4. Choose the Type.
5. Enter the Item Name, then choose the Account.
6. Click on OK.

Once done, you can now add the mark up to your invoice.

Please know that you can always get back to me if you have other questions. I'd be happy to help.