1040 instruction page 62

The total of lines 64, 65, and 67 on your 2006 return is at least 100% of the tax shown on your 2005 return (110% of that amount if you are not a farmer or fisherman and your adjusted gross income shown on that return is more than $150,000, or if married filing separately for 2006, more than $75,000). Your estimated tax pay ments for 2006 must have been made on time and for the required amount.

well. it depends on how much you decide to withhold in the second year.