Student Loan Interest: Why Payments Don’t Touch Principal

Millions of Americans make their student loan payments on time every month and still… somehow… the total amount they owe might not ever go down. 

It might even go up.

This is not a glitch, and it’s (somehow) not illegal. It’s the system: a result of how interest on federal student loans is structured. You need to understand the mechanics; otherwise, you’re doomed in the cycle of debt, perhaps forever.

These loans are not like car loans. They actually are more like a mix of predatory payday loans and something you’d get from a loan shark. That’s not a joke. 

They’re like payday loans in that you, the borrower, have no established credit history or income, and the industry bets on the promise of future earnings—that is, you paying this debt forever. You’re being asked to take on disproportionately large amounts of debt compared to your immediate ability to pay it back. And just like payday loans, student loans often trap borrowers in cycles where they are only paying interest or watching their balances balloon, leading to decades of debt.

Student loans are like a loan shark’s loans in their combination of compounding interest and aggressive, unyielding collection. It creates a scenario where the lender almost always gets their money back, no matter how much it ruins the borrower’s life. Like loan sharks, the federal government and private lenders have extraordinary powers to collect. They won’t break your legs like a loan shark, but they can garnish wages, intercept tax refunds, and seize Social Security benefits without a court order. 

For veterans managing the demands of military transition alongside complex financial obligations, a bad student loan can do more harm than good. 

How Student Loan Interest Works

Federal student loan interest doesn’t sit idle while borrowers are in school, in a grace period, or in deferment. It accrues daily, whether you’re in school or not, and it starts almost immediately. This formula is straightforward: the outstanding loan balance is multiplied by the annual interest rate and then divided by 365. 

On a $10,000 loan carrying a 6.39% interest rate (which was the rate set by the U.S. Department of Education for undergraduate direct loans in the 2025–26 academic year), that amounts to roughly $1.75 in interest every single day, or approximately $53 per month.

When borrowers don’t pay the accruing interest before it capitalizes, the unpaid amount is added to the principal balance. Once capitalization occurs, interest then accrues on the new, larger balance, meaning borrowers are effectively paying interest on interest. 

A borrower who graduates with $10,000 in unsubsidized loans at 10% and does not pay during school or the six-month grace period can see their principal balloon to $10,750 before making a single payment on the underlying debt.

Negative Amortization

The term "amortization" refers to the process of reducing a loan balance through regular payments. Negative amortization is the (infuriating) inverse: the balance grows even when payments are being made because those payments don’t cover the interest accruing each month.

That means that even when you pay, the total amount you owe will still go up because you are not paying enough to cover the interest. 

As if that wasn’t bad enough, on federal student loans, payments are always applied to interest before principal. If a monthly payment doesn’t satisfy the interest due that month, not one dollar touches the underlying loan balance.

Income-driven repayment (IDR) plans are the most common setting in which this occurs. Under IDR, payments are calculated as a percentage of a borrower's discretionary income rather than based on the loan balance. For borrowers with low incomes relative to their debt loads, that payment can be $20, $10, or even $0 per month, far less than the interest accruing daily. 

On a $10,000 loan at 3.65%, a borrower who qualifies for an IDR payment of just $5 per month would be covering almost none of the roughly $30 in monthly interest, causing the balance to grow every month despite active participation in a repayment program.

Remember this every time someone on Twitter says, “You borrowed the money, you have to pay it back.” 

The Scale of the Problem

The numbers behind this phenomenon are astonishing. Americans collectively owe $1.833 trillion in student loan debt as of 2026, with 42.8 million borrowers carrying federal loan balances. 

The average federal student loan balance stands at $39,547. Meanwhile, student loan delinquency rates are high: 10.3% of student loan balances were 90 or more days delinquent in the first quarter of 2025.

Student debt in the United States has more than doubled since 2008, when the outstanding balance stood at roughly $600 billion. That growth has significantly outpaced the rate of enrollment changes, suggesting that interest accumulation, not simply more students taking out more loans, is the real driver of the overall debt burden.

Triggering Events

Triggering is the right word. Negative amortization and interest capitalization strike at predictable moments, all of which are major life events, when you might not be thinking about student loan interest rates.

The most common capitalization events occur when a borrower exits a grace period after leaving school, when a deferment or forbearance period ends, and when a borrower enters, leaves, or fails to recertify an IDR plan annually. 

In each of those scenarios, any unpaid interest sitting in a borrower's account is added to the principal, locking in the damage and enlarging the base on which future interest will accrue.

The standard 10-year repayment plan generally prevents negative amortization because monthly payments are calibrated to cover interest and reduce principal. 

The danger arises most acutely when borrowers opt for lower-payment alternatives, pause repayment entirely, or find themselves in administrative limbo due to servicer errors—all of which are very common.

Because life does not always go according to your 10-year plan.

Student Loans for Veterans

Veterans navigating the transition from military service to civilian life face unique exposure to life events that can trigger both capitalization and negative amortization. 

Deployments, Permanent Change of Station moves, and the search for post-military employment can all disrupt a veteran's ability to stay current on student loan payments or even to track their growing balances. 

Veterans represent a significant share of the borrowing population. A White House memo issued in 2019 noted that around 50,000 totally and permanently disabled veterans qualified for federal student loan discharge, but roughly half had not claimed that benefit. 

More than 42,000 veterans with severe disabilities hold a combined $1 billion or more in outstanding student loans, with more than 25,000 of those veterans in default on $168 million in debt. 

Default, it should be noted, is frequently preceded by years of negative amortization and balance growth that make repayment feel hopeless.

Veterans using the GI Bill still carry student loans. A full 24% borrowed federal or private student loans in 2015–20616, with an average annual loan amount of approximately $7,930. Even at relatively modest balances, the compounding effect of interest on an income insufficient to cover monthly charges can push a manageable debt into a seemingly unresolvable one.

Regulation Will Not Save Us

Policymakers have made intermittent efforts to address negative amortization. The now-contested SAVE plan, the Biden administration's most recent IDR program, included a provision to fully subsidize unpaid interest for borrowers whose calculated payments did not cover accruing interest, which prevented balance growth. 

That’s gone.

Federal courts blocked the SAVE plan, and as of publication, borrowers previously enrolled in SAVE are being transitioned to other repayment options. The Education Department warned that loan balances will grow when interest starts accruing again for SAVE-plan borrowers

In January 2026, the Department of Education issued a Notice of Proposed Rulemaking tied to the Working Families Tax Cuts Act, aimed at simplifying repayment and introducing a new program called the Repayment Assistance Plan, or RAP. 

Set to launch July 1, 2026, it will replace all other IDR options for new borrowers by 2028. Limited data makes it difficult to project RAP's full effects on borrower outcomes, but if the history of student loan law is any indication, it’s probably not going to save anyone.

What Borrowers Can Do

The most reliable protection against negative amortization is straightforward: avoid student loans at all costs. If you have to take a student loan, pay at least the interest accruing on a loan each month, even while in school or during a grace period. 

Borrowers who can’t afford full payments should contact their loan servicer to explore IDR options, which may include interest subsidies, and need to remember to recertify annually to keep payments current with their income.

Veterans, in particular, may be eligible for benefits that go beyond standard repayment assistance, including total and permanent disability discharge, Public Service Loan Forgiveness for those who have served in qualifying government roles, and service member-specific deferment provisions. 

Everyone needs to understand what makes student loans unique and use official federal tools—specifically, the loan simulator at StudentAid.gov—before taking one out. Or enrolling in any repayment plan.

Now that you understand student loan debt, it should make you feel like risking your life for education benefits wasn’t such a bad trade-off.