Hello, mmarecle.
I'll share some details about the effects of uploading your credit card charges in QuickBooks Desktop.
If you're referring to the manual upload (WebConnect method), then the existing uploaded transactions will be doubled. The new transactions will be added normally.
If you don't want duplicates, I would recommend formatting your file to exclude those you already uploaded in QuickBooks.
You can also do it through your bank's website as well. Just set the date range and filter out the transactions if possible before downloading your file format.
If you're trying to download those transactions through the Bank Feeds Center, then they won't be doubled. Only the new charges will be added. The Bank Feeds system will only download a certain set of transactions once.
More details can be found here:
Do you need help managing and categorizing your transactions? This article can guide you: Add and match Bank Feed transactions in QuickBooks Desktop.
If you also need help with your reconciliation, feel free to use this article as a workflow guide: Reconcile an account in QuickBooks Desktop.
I'll be around to help you out again with your credit card transactions or the Bank Feeds feature (and any other things in QuickBooks). Just say the word below and I'll get back to you.