Taxpayers will likely wait 15 years until Fannie Mae and Freddie Mac repay their bailouts in full, according to the more optimistic forecast from Moody's Analytics.

Fannie turned its first profit in the first quarter since entering conservatorship in 2008. Freddie Mac has been operating at or near break-even for roughly six months. The improved performance prompted some to explore when the money will be paid back. Along with Freddie, the government-sponsored enterprises drew $189.5 billion from the Treasury Department as of March 31 and paid $41.1 billion in dividends.

There are many factors to consider. House prices remain fragile, which could diminish value in the massive but shrinking GSE portfolios. Higher guaranty fees could produce more income, but any setback to the economy could spark more defaults. The only thing that seems certain is inaction from Washington to reform the mortgage giants in the near term.

"Taking all these factors into account, a credible case can be made that the GSEs could repay their debts within 15 years, given the current market trajectory," said Cristian de Ritis, director at Moody's Analytics, in a recent blog post.

He estimates the cost of the GSE bailout would be $200 billion, roughly 10% more than the government commitment made to rescue American International Group (AIG). In October, the Federal Housing Finance Agency, using Moody's data, estimated the GSEs would need to draw between $220 billion and $311 billion under different scenarios.

And de Ritis offered different scenarios himself. Optimistically, he said, if the GSEs require no future draws from the Treasury going forward – meaning they make enough profit to clear their 10% dividend payment – it would still take until 2019 to pay back the $148.5 billion still outstanding.

The Obama administration projected Fannie and Freddie would need $221 billion by the end of 2013, according to its budget proposal. Under this scenario, de Ritis said the repayment date moves out to 2021.

Still, there are even dimmer realities, which could push out the repayment date not by one decade but two.

"Fannie Mae earned a total net profit of $33 billion from 2000 to 2005, so the assumption that the firm could earn $129 billion over the next 10 years seems like a stretch," de Ritis notes. "Assuming that Fannie's earnings are similar to what they were from 2000 to 2005, the time required to repay the Treasury extends to 2033."

Congress would likely act by then. Either the two firms will be broken up into smaller versions with some form of a government guarantee either on the bonds they issue or the companies themselves, or lawmakers could elect to turn the entire mortgage market over to private firms. There is no forecast for this outcome, but de Ritis explained for the time being, it is likely to remain the status quo. Some lawmakers and Treasury officials have concluded the GSEs may never pay back the funds.

"While the GSEs clearly made some poor decisions, private investors didn't fare that much better," de Ritis said. "Keeping the agencies under federal control, where they may be closely monitored, seems to be the preferred strategy at the moment."