I’m in school and my loans are growing.

The meter started the day the money arrived.

Nothing went wrong. On most student loans, the interest starts adding up the moment the money is disbursed (sent to your school): it accrues from day one, not from graduation or the first bill. Every month you sit in class, a little more is charged on what you owe, which is why the balance reads higher than the amount you signed for even though you haven’t borrowed another dollar.

The good news: this is the cheapest moment in the whole life of the loan to do something about it. The amount is small now, and one habit started today keeps it from quietly compounding into something much larger by the time you owe your first payment.

One word decides whether the clock is yours.

Federal student loans come in two flavors, and the difference decides who pays the interest while you’re enrolled:

• Subsidized. The government pays the interest for you while you’re enrolled at least half-time (and during the grace period). The balance holds steady at what you borrowed. These go to undergraduates with financial need.
• Unsubsidized. The interest is yours from day one. It accrues the entire time you’re in school, whether or not you pay it. Most graduate loans and a large share of undergraduate loans are unsubsidized.

So the first move is to find out which ones you have. Log into studentaid.gov and look at each loan: it’s labeled “Direct Subsidized” or “Direct Unsubsidized.” The unsubsidized ones are the only ones growing on you, and they’re the ones worth your attention.

The quiet part is what happens at the end.

While you’re enrolled, the interest quietly piles up — it’s already part of the balance you watched climb on your dashboard, but it hasn’t yet been folded into your principal (the original amount you borrowed). The trap springs when you enter repayment: that accrued interest is capitalized, added onto the principal itself. From that day forward you’re paying interest on the old interest, and the whole balance grows faster.

Same four years of borrowing, two different habits. Pay the interest as it builds and you start repayment owing exactly what you borrowed. Let it ride and the capitalized interest is baked into your balance before you’ve made a single payment — and you’ll pay interest on it for years. The exact figure depends on your own balance and rate; the payoff tool below finds yours.

A few dollars a month keeps it from ever catching.

You aren’t required to pay anything on student loans while you’re in school. But on an unsubsidized loan, paying just the interest as it accrues holds the line exactly where you borrowed it: nothing capitalizes, because there’s no unpaid interest left to capitalize. On a single year’s loan that interest is often only twenty or forty dollars a month; across a few years’ balances it’s more, but the payoff tool below shows your exact number.

See what the interest is actually costing.

The monthly interest on an unsubsidized loan is a small, knowable number. Put your balance and rate into the payoff tool and you’ll see exactly what’s accruing each month — the amount a small in-school payment would erase before it ever has a chance to capitalize.

One move this week.

You don’t have to fix the whole loan today. One small step does almost all of the work, and it’s the kind of thing that’s easy to set once and forget.

Log into studentaid.gov to see which of your loans are unsubsidized and who services them, then go to that servicer’s site and set up an automatic monthly payment for the interest. It’s a few dollars a month, it stops the balance from growing, and it spares you the capitalized interest you’d otherwise carry for years after graduation.