We have five kids so over the years our taxes have always been minimal due to the additional exemptions and tax credits provided by children. When I was early in my career and only making about $35k we qualified for the earned income tax credit for a few years and between that and child tax credits we ended up getting back all of the taxes that were withheld throughout the year, plus a few thousand more. I think one year we had a negative 12% tax rate. These days our effective tax rate is still close to 0% even though my income has doubled.

Bottom line is that you want to get your taxable income as low as possible. That's the number that you're paying 10%, 15%, 25% and so on. Your gross income can be lowered through deductions and exemptions. Your taxes can be reduced through credits, some of which are refundable. So if you owe $900 in taxes and have a $1,000 refundable tax credit you'll get $100 back, if it's non-refundable you'll just owe $0.