Estimated Tax Safe Harbor

[David]

Client's 2010 1040 had income tax of $9,134 and SE tax of $12,928, for total tax of $22,062. Projected 2011 tax is income tax of $19,500 and no SE tax. (switched to an S-corp. for 2011)
One of the provisions of the safe harbor rule is "100% of the tax shown on the 2010 return..." Does 'tax' mean income tax or total tax?
So, is the required estimated tax payment for 2011:
100% of $9,134 = $9,134
or:
90% of $19,500 = $17,550

Thanks for your help.

[Gary2]

It means total, mostly. To be precise, see Form 2210 and its instructions. In your case, it would be the $17K number.