Okay, here’s what I see. I didn’t ask you about filing status, but with line 43 taxable income of $15k, you’re in the 10% or 15% brackets regardless, which means you’ll pay zero % cap gains rate on your lines 9b & 13 amounts (3450 + 19403 = 22853), assuming all cap gains are long term. Notice how that amount is larger than your line 43 figure of $15k.
The way IRS sequences deductions, they apply first to ordinary income. So, based on what you’ve told me, for you to have a $15k taxable income figure, that means you had sufficient exemptions & deductions to whittle your ordinary income down to zero, including any short term cap gains you might have had. Then those deductions started whittling down the long term cap gains, so the $15k that’s left is entirely made up of LTCG. This includes an assumption on my part, that no more than 1/4 of your cap gains were short term.
In this scenario, zero tax on $15k of taxable income does make sense.
