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.