Hello again Vickie,
The tax free limit for the 2010 tax year has increased to $91,500. He would only receive the full amount if the 330 days that he was overseas was all in the same calendar year. Here is another example of how it works.
Let's say that your son went overseas on July 1st, 2009 and stayed there until July 1st, 2010 for a full year. Even though he was there for the required time of at least 330 days in a 12 month period, those days were not all in the same calendar year. He spent 6 months there in 2009 and 6 months in 2010. What that means is that he could claim 50% of the credit on his 2009 income and 50% of the credit on his 2010 income. The credit in 2009 was $91,400, so for the 2009 tax year he could claim half of that amount, or a total of $45,700. So his first $45,700 in foreign earnings for 2009 would not be taxable. It is correct that the wages are still subject to SS and Medicare taxes.
Since you son arrived in Afghanistan on November 8th, 2009, he would satisfy his 330 day requirement if he stays there until October 4th. But just because he satisfies the 330 day requirement does not mean he would get the full credit of $91,500 for the 2010 tax year. He would get a prorated portion for the actual days he was out of the country in 2010. The days he was out of the country in 2009 only go towards satisfying his 330 day requirement in a 12 month consecutive period, but they do not count towards the credit. He would only be credited for being out of the country for the days he was gone in the 2010 tax year. So if during 2010 he was gone for 10 months, basically he could claim 10/12ths of the credit, or a total of $76,250. If he wants to claim the entire credit of $91,500 for 2010, then he must remain out of this country for the entire 365 days in the 2010 tax year.