Is that the tax on line 12 or the tax due to pay? I don't see that amount on the tax table https://www.irs.gov/pub/irs-pdf/i1040tt.pdf
Some reasons could be you had more qualified capital gains in 2018. Or in 2019 you have a penalty for something like the 10% Early Withdrawal Penalty on a IRA or 401K distribution. You need to post the line numbers.
