Can you add an existing invoice to an estimate?

Hi, judy.

In QuickBooks Online, you can only create an invoice from an estimate. The option to add an existing invoice to an estimate is currently unavailable.

Also yes, you can see already billed amounts on a progressive invoice. To do that, I recommend running the Estimates & Progress Invoicing Summary by Customer report.

Here's how:

1. Log in to your QBO account.
2. Go to the  Reports menu.
3. Search and click to open the Estimates & Progress Invoicing Summary by Customer report.

You can check this article for more information about creating progress invoices from an estimate: Set up and send progress invoices in QuickBooks Online. It'll also guide you in reviewing your estimate, progress invoices, and projects, and creating reports.

Once you're done creating an invoice and receiving your customer payments, here's how to record invoice payments in QuickBooks Online.

I'm always here to help if you have any other questions about invoices or any other questions about QuickBooks.

I was looking to do this also and found a way to do it if you have progress invoicing set up.  I clicked on Suggestions and it brought up the Estimate that I was wanting to link.  I clicked add and selected manual amounts per line.  Then I deleted the duplicate lines and it kept the invoice linked to the estimate for the exact amount that had been paid when I saved it.