If the student loan belongs to just one of you, then allocate the full amount to the one it belongs to. If you each have a student loan, I would suggest you allocate the $2,500 based on your percentage of the total loan interest.
For example, if your loan interest is $6,000 and your spouse's loan interest is $4,000, then you would have a 60/40 split of the $2,500 you are allowed to deduct.
