Assuming you are not self employed (which would definitely trigger this) the most likely reason is that you owed more than $1,000 on your tax return so you will have to make payments to avoid a penalty next year. If you have taxes taken out of your paycheck you should consider completing an adjusted W4 with your employer. You can see if ttax created a form 2210 in your return, that should give you a clue. There are other variables (e.g. if you are a fisherman or farmer by trade) but assuming that you work for an employer and receive a W2 you probably just didn't have enough taxes taken out during the year
