From WAPost: We STILL don't know what percent of taxes Mitt actually paid over the 20 years.

Why? Because all the Price Waterhouse letter-writer did was average the various rates Mitt paid each year -- but that doesn't take into account which years Mitt had high incomes, and which years he had SUPER high incomes. If he had SUPER high incomes the same years he had the lowest taxes (which is likely), then his overall rate of taxation could be much lower than the 20% figure they're claiming now.

http://www.washingtonpost.com/blogs/plum-line/post/expert-romney-may-have-paid-less-in-taxes-over-20-years-than-it-appears/2012/09/21/41b27e00-041e-11e2-91e7-2962c74e7738_blog.html

SNIP


Roberton Williams, a senior fellow at the nonpartisan Tax Policy Center, tells me there are two ways to calculate it. First, the campaign could simply have averaged the rates against each other — treating the rates themselves as a collection of individual numbers — to calculate the overall average rate.

The second way to calculate it would be to add up all the income Romney earned over the 20 years, add up the total amount he paid in taxes during that period, and calculate the overall average rate paid that way.

The Romney campaign confirmed to me just now that the 20 percent figure was calculated the former way — it represents an average of the rates themselves.

Williams tells me that this is a far less meaningful way to calculate the overall rate than the second way, which actually calculates the real tax rate Romney paid over the period.

SNIP