I've been getting the question in the title to this post, and no one can really answer it without seeing the return itself. But let's take another look at the 2010 return, and see what we can glean from that.
In 2010, Romney paid just over $3 million of tax on $21.6 million of adjusted gross income. Hence, the widely quoted 13.9%. tax rate, which is simply $3M divided by $21.6M.
The main components of the $21.6M were as follows:
(1) About $12.6 million of net capital gain, the great majority of it long-term capital gain (including carried interest payments from Bain) that gets taxed at 15 percent. However, the gross amount of Romney's 2010 capital gains was almost $5 million higher than this. He reduced the net inclusion by deducting $4.8 million of capital loss carryovers from 2009. (If one ignored this deduction and recomputed his 2010 effective rate, it would be $3M / $26.4M , or about 11.4%. See below for discussion relevant to whether one should so recompute it.)
(2) About $3.3 million in interest income, plus $4.9 million in dividends, plus just under $600,000 in Schedule C business income, mainly for speaking fees. So his "ordinary" income (including that which qualified for the 15% tax rate on dividends) totaled about $8.8M, yielding the $21.6M total once one throws in miscellaneous odds and ends.
Okay, let's run the tape in reverse and see what we can figure out about 2009. The gross capital gain may have been significantly higher in 2009 than in 2010, because he was still receiving other payouts from Bain that I would think could have been structured to yield capital gain. [UPDATE: This may be incorrect - the arrangement appears to have been that he'd receive payouts on Bain deals that occurred through 2009, not that he'd receive payouts until 2009 on Bain deals. So perhaps we might expect the gross capital gain for 2009 to be similar to those in 2010, or perhaps lower given overall economic circumstances, rather than higher.)
In any event, we know from the capital loss carryover in the 2010 return that his net capital gain inclusion for 2009 was zero (or more specifically he was allowed to deduct a net capital loss of $3,000). As I've noted in earlier posts, this presumably reflected loss harvesting - the sale of "loss stocks" that presumably had gone down in the 2008-9 stock market collapse, although he may still have retained in his portfolio lots of still-appreciated stocks that he had bought years earlier when the stock market was significantly lower.
OK, so if we are asking what his effective tax rate was in 2009 (the analogy to the widely accepted 13.9% figure for 2010), even if we had the return, this question wouldn't answer itself. We would have to ask ourselves: What is the denominator (i.e., income for the year). Do we want to say zero, despite the gross, as opposed to net, capital gains? Obviously income is a net, not a gross, concept, and the stocks that he sold presumably did really lose value. But with loss harvesting you have to think about the overall portfolio and how it was performing over a longer period of time. (His tax return wouldn't show that, of course.)
So far, this sounds like a scenario that Romney could defend if he released the 2009 return. He has no net capital gain, pays no tax on it, says that this is legitimate because he had stock market losses, and the riposte that he may have used loss harvesting to report losses against a background of overall stock appreciation over a period of years is a bit too refined to do him much political harm.
But could he have paid zero overall in 2009? This would have required zeroing out the ordinary income, which can't be offset by capital losses. Again, in 2010 all this other income added up to about $8.8M. His reluctance to release his 2009 return would suddenly be a lot more understandable if it turned out that he had questionable tax shelter losses offsetting the 2009 equivalent of this income. We have absolutely no direct evidence that he did anything like this. What's more, it would have been irrational for him to engage in this stuff in between presidential runs, and one wouldn't think he'd be irrational. But again, the mystery of his reluctance to release anything further openly invites otherwise unfounded speculation.