I’m in the military and file through MD for state taxes and I owe but have never owed before and don’t know why

We cannot see your tax information and without knowing all the details there is no way to know why it is different. You might want to compare line by line this year's state tax return with the previous year's state tax return. You can access a tax summary by following the steps below:

1. Click on "Tax Tools" in the left menu
2. Click "Tools"
3. Click "View Tax Summary" in the Tool Center window
4. Click on "MD Tax Summary" on the left

If you want someone to review your tax return you always have the option to add TurboTax Live: What is TurboTax Live?

If your HOR is MD, then MD taxes all your income, including Military pay.....

Except:

1)   Combat pay  (box 12 code Q on your W-2)

2)  IF you are stationed overseas (in a non-combat posting), then up-to 15,000 of that overseas pay is exempt form MD taxation.

First edit your W-2 and make sure you have checked the box that it is a military W-2 on the page that follows the main form.....its a page with a whole big list of check-boxes, and the Military W-2 checkbox should be the first one at the top.  (if it isn't there, then you didn't fill out the My Info section properly )

Then fill in all your Federal information before going to the MD section....the "stationed overseas" question should be asked when you go thru that section  (either that, or one of the pages after the W-2 was entered in the Federal section)....but maybe you were not stationed overseas last year...then the $15,000 deduction wouldn't apply to MD for 2019....and maybe you just owe MD this year.