We underpaid a lot this year for the first time

Hi.

My wife has a base salary and also gets bonuses later in the year. This was the first year she received bonuses as she just started 1.5 years ago. I also started my own business this year and had a small loss.

This is the first year we had to pay more in federal taxes. We were off by quite a bit too. We claimed 6 exemptions this year on my wife's w4. If we had claimed 0 would that have given us a return or put us closer to breaking even.

I guess my question is, if my wife's employer is withholding taxes how the heck did we get so far off? Was it our fault for sampling flaming way too many allowances? 


Thanks