How to assign mileage rates to my business milages entered into QB, and get it to automatically added as an expense?

Hi adster02-ap,

It's nice to see you reaching out here.  Welcome!  QuickBooks Online Mileage feature is a great way to track business miles effortlessly.  I'll be happy to provide more information so you're on the right track!

You can automatically track your mileage so you have everything you need at year end.  Turn on your QuickBooks mobile app when you start driving to track your miles from start to finish.  After you've reached your destination you can categorize, review, edit or export your trips as outlined in this guide.  

Feel free to contact us if you have any other questions or concerns with mileage.

Schedule a Callback or start a Chat: click (?) Help in the upper right in QuickBooks Online > enter "Contact support" > hit Contact Us > provide a brief summary of your situation > hit Let's Talk > choose Get a callback or Start a Chat.
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Cheers!