What Happens to Unpaid Interest Under an Income-Driven Repayment Plan?
It sounds contradictory that a borrower can make every payment on time and still watch a loan balance not shrink, or even grow, but that outcome is a fairly ordinary feature of how income-based payments interact with interest.
The short answer
An income-driven repayment plan sets the monthly payment based on income rather than on what’s actually needed to pay off the loan on a set schedule. When that income-based payment is smaller than the interest accruing that month, the shortfall — the unpaid interest — doesn’t simply disappear. Depending on the specific plan’s rules, it may get added to the balance, may be partially or fully subsidized so it doesn’t compound, or may simply accumulate separately, and those rules vary by plan and have changed over time.
Why a payment can be smaller than the interest
Interest accrues on a loan balance continuously, calculated from the interest rate and the outstanding amount owed. An income-driven payment, by contrast, is calculated from a percentage of income above a certain threshold, with no direct link to the loan’s rate or balance. Someone early in a career, between jobs, or working in a lower-paying field can have a calculated payment that’s genuinely small — sometimes smaller than a single month’s interest charge on a larger balance. That’s not a sign of doing anything wrong; it’s simply how a formula based on income, rather than a formula based on debt payoff, behaves when the two numbers don’t align. This is the same underlying idea that appears in how switching repayment plans changes total interest paid over the life of a loan.
What “capitalizing” interest generally means
When unpaid interest gets added to the principal balance, that’s often described as capitalizing the interest — the loan effectively grows, and future interest is then calculated on the new, larger balance rather than the original amount. This is a version of compound interest working in the borrower’s disfavor: interest accruing on interest that was never paid off. Some income-driven plans include features meant to limit or delay this kind of capitalization, such as covering some or all of the unpaid interest for a period, but the specific protections and how long they last are determined by program rules that are set by the government and subject to change.
Why the balance can grow even with on-time payments
A rising balance under an income-driven plan often surprises borrowers who assume that making payments automatically means making progress. The reality is that a payment can satisfy the plan’s requirements — avoiding delinquency, keeping the loan in good standing — without covering the full cost of carrying the debt that month. Making extra payments under an income-driven plan, when financially possible, is one of the few direct ways to counteract this and put money toward principal rather than only toward the required amount.
Why this can still be a reasonable tradeoff
For a borrower prioritizing an affordable monthly payment over minimizing total cost, a growing balance during a low-income stretch isn’t necessarily a mistake — it can be the intended tradeoff, particularly on plans connected to forgiveness after a set number of qualifying payments. The key is understanding that the tradeoff exists, rather than assuming the loan is shrinking simply because payments are being made consistently.
What to weigh
Before assuming a low income-driven payment is a pure win, it’s worth checking whether unpaid interest is capitalizing, whether the specific plan offers any interest subsidy, and how that balance trajectory fits into the borrower’s longer-term plan for the debt.