A refund or tax due is related to how much tax withholding and/or estimated tax payments you have made. A better measure is to compare the total tax liability between the two years.

Compare 2017 Form 1040 line 63, or 1040A line 39, or 1040EZ line 12, to 2018 Form 1040, line 15. Barring any material income increases or deduction decreases, most people should see a reduction in total tax.