This is a hugely complicated question and I can’t even suggest where to go to look for an expert to help you answer.
If you are counting on making reduced payments through income-based repayment (IBR) for the minimum period of time and then forgiving the rest of the loan, then filing a joint tax return will almost certainly increase your payment requirement. However, filing a joint return has lower tax rates and better deductions, because some deductions and credits are limited or even disallowed when filing separately. When you get into having children, filing separately is an even greater disadvantage. Filing separately also impairs your ability to save for retirement through IRAs. Then, whatever part of the loan is forgiven, may end up being taxable income on your tax return for the year in which the loan is forgiven, although this depends on exactly which forgiveness program you are enrolled in.
You could be in a situation where the amount of tax you cost yourself by filing separately over the next 10 or 20 years is more than the loan payment savings, or where the tax on the loan that is forgiven at the end of the 10 or 15 or 20 year period overwhelms any savings you incurred in the meantime. Not to mention the changing political environment could change any of these factors without warning.
It’s complex and I don’t know offhand any financial planner or tax expert who would be able to foresee and calculate all the possibilities for you. Good luck.
