"without changing anything I suddenly owed $7860."
I know the software this year had trouble keeping up with the changes, but I'm trying to locate the reason. If I had the two returns (pre-and-post changes), I'd find the specific line where the new, large liability appeared.
Do you get your insurance from the Marketplace Exchange? (aka Obamacare)
Are you self-employed?
Were you eligible for any subsidy from the ACA?
Were you eligible to put any money in a Traditional IRA?
The reason I ask, is numerous times this year, I saw this scenario play out. We usually ameliorated the large tax bill by putting money in a SEP-IRA. But the intersection of the questions I asked can often cause a HUGE single-dollar trigger.
Last year, I found a spot where one extra dollar in the retirement fund saved $3800 in income taxes.
This year, that record was smashed: I found a one-dollar trigger for $7508. There was a point where the taxpayer literally had the choice between paying the IRS $6K, or paying himself $6K via a SEP-IRA.
Then, three days later, the original record holder reclaimed the crown: I found a one-dollar trigger for $10,548. I walked my assistant through it, just so I'd have a witness.
Most effed up code I've ever seen, by a long shot.