Income-Driven Repayment flips the usual loan repayment logic on its head: instead of your monthly payment being calculated from how much you owe, it's calculated from how much you earn. * Under IDR, your payment is set as a percentage of your "discretionary income" — a calculation that first accounts for basic living expenses based on your family size, then applies a percentage to whatever income remains above that. For borrowers with low income relative to family size, this can mean a monthly payment of $0, while still counting as a "qualifying payment" toward eventual forgiveness. * Because the calculation is based on income and household size rather than your loan balance, your payment isn't locked in forever — it gets recalculated every year based on your current situation. Get a raise, and your payment can go up. Have a child or see your income drop, and your payment can go down. * IDR isn't a single plan — it's a category covering several federal plans with slightly different formulas and eligibility rules, so the exact percentage of discretionary income and forgiveness timeline can vary depending on which specific IDR plan you're enrolled in. * The long-term payoff for staying enrolled is forgiveness: after a set number of years of qualifying payments, any remaining loan balance gets forgiven entirely. One detail that changed recently and matters for planning: beginning in 2026, student loan debt forgiven through IDR may be treated as taxable income, unlike the tax-free forgiveness treatment that applied in earlier years.