It is unclear why I had a fed tax REFUND of 108 on income of 11,798 in 2017 -- BUT a tax of 423 on income of half that sum, 6036 for 2018. It is concerning

[AnthonyC · Accepted solution]

Did you have a Form 1099MISC or other self-employment income?  I notice you are posting from TurboTax Self Employed.  If so, you likely owe self-employment taxes and this is the reason you owe taxes.  Self-employment taxes are roughly 15% of your net income and they comprise the social security and Medicare taxes that you would normally see withheld on your paycheck for a W2 job.

While your standard deduction can decrease your taxable income from income tax purposes, it does not reduce your net income for self-employment tax purposes.  So, this is why you may owe taxes on less income.