Slight correction ot Hal Al's reply. Only the first $2,000 of an individual's retirement contributions is considered for the credit (line 6 of Form 8880). If your AGI is not over $41,000, with a $4,000 contribution to just your IRA the credit would be 50% of $2,000 which is $1,000, not 50% of $4,000. To get to a total credit of $1,510, your spouse would have to contribute at least $1,020, to your spouse's retirement account; 50% of $1,050 is $510.
