Good Evening,
Both my wife and I have comparable (~$33K) federal student loan debts and are looking into IBR.  We are MFJ on our taxes and have comparable salaries as well.  As I understand it, under IBR we would be paying 15% EACH of our discretionary income, for a cumulative total of 30%.  Am I mistaken?  I certainly hope so….

Married student loan borrowers can choose to either:
• file taxes jointly and have monthly payment based on joint AGI and combined student debt, or
• file taxes separately and have monthly payment based on individual AGI and individual student debt  
If a married couple files a joint federal tax return, a total student loan payment amount for the couple will be calculated taking into account both spouses’ debt and both spouses’ income.  A proportion of the total payment will be assigned to each spouse based on their share of the couple’s total student loan debt.

So no, the IBR payment will be 15% of joint discretionary income, and each spouse will be required to pay a portion of that payment towards his or her loans.  For example in this case, if each spouse owed 50% of the combined debt balance, then each would be half of the calculated payment.