How do I add a custom field to a journal entry?

I don't think the Journal entry form is customizable. It's really not intended for regular use.

That is strange...we use JEs all the time for accruals, allocations, depreciation, etc.   

Interesting and odd to me...we use JEs all the time to record transactions such as accruals, allocations, depreciation exp, relcassifications, etc.

Thanks for your prompt reply, cpadula-deverrat.

In addition to BigRedConsulting's answer, adding a custom field is only available for all sales forms and purchase order. You'll want to send a suggestion to our product developers. They'll review this idea and might consider updating it in the future.

Here are the steps:

1. Go to the Gear located at the top.
2. Under Profile, click Feedback.
3. Enter your suggestion and select Next to send your request.

If you want to check the status of your request, you can click this link: Customer Feedback for QuickBooks Online.

To learn more about custom fields, please check out this guide: How to add custom fields to sales forms and purchase orders.

You're welcome to post a reply if you have any additional questions or other concerns in your account. We're here to help you out some more. Have a good day ahead.