I always end up getting a federal refund when filing taxes. I want to adjust my deductions so that I try to hit as close to $0 as possible so I don'tpay in or receivea refund, but I was reading that there is a penalty interest for underpayment. How does that work because I often hear of people oweing in at tax time; are they being charged the penalty interest on the amount they underpaid by? Also, I was told you can no longer put a general number for federal deductions- how do you figure an exact dollar amount, I always end up paying $450 on every paycheck for federal, am I safe to just put $450 or how does that work. Thanks in advance for the help!