IBRinfo.org is a great website and I've put some of their information below:
Income-Based Repayment (IBR) is a new payment option for federal student loans. It can help borrowers keep their loan payments affordable with payment caps based on their income and family size. For most eligible borrowers, IBR loan payments will be less than 10 percent of their income - and even smaller for borrowers with low earnings. IBR will also forgive remaining debt, if any, after 25 years of qualifying payments.
Who can use IBR? IBR is available to federal student loan borrowers in both the Direct and Guaranteed (or FFEL) loan programs, and covers most types of federal loans made to students, but not those made to parents (click here for more about qualifying loans). To enter IBR, you have to have enough debt relative to your income to qualify for a reduced payment. That means it would take more than 15 percent of whatever you earn above 150% of poverty level to pay off your loans on a standard 10-year payment plan. Use our calculator to see if you're likely to be eligible.
How does IBR make payments more affordable? IBR uses a kind of sliding scale to determine how much you can afford to pay on your federal loans. If you earn below 150% of the poverty level for your family size, your required loan payment will be $0. If you earn more, your loan payment will be capped at 15 percent of whatever you earn above that amount. Except for the highest earners, that usually works out to less than 10 percent of your total income.
This chart shows examples of IBR payment caps as a percentage of the borrower's family income, based on various incomes and family sizes.