They base your monthly payment on your income and family size. You have to submit tax documents and apply every year. It's possible to have a payment set at zero.
Some caveats:
Have to apply every year and early enough for renewal so you don't lapse in the plan.
It only takes into account Federal loans, so if you have a large amount of private loans, your total payments could still be high.
IBR is not always the cheapest plan. I'm now on income sensitive repayment since that was about $100 less than my new IBR payment. So check all of your options.
---In order to switch plans I had to make a full regular monthly payment ~$350. I was able to pay it, but some might not.
It's possible that at some point you won't qualify any more
---But if you always qualify for IBR, after 25 years of payments, the balance of your loans is forgiven.
Starting Score: 515
FYI, There is another option with the ICBR program. If you work for a governmental agency (local, state, federal) and you're in the ICBR or other applicable programs and you make 120 payments, you can have any portion of your loans not paid after that time forgiven under the Public Service Forgiveness program. The best part about this program is that any amount forgiven is NOT taxable. Please see link below.
(Formerly known as: Credit is my hobby/TCL objective)Almost forgot, some non profits qualify for the Public Service Loan Forgivness program too.