$25,000 at $520 a month — what interest rate is that?

If it's a five-year loan, they're charging you about 9.1% — and you'd hand back $31,200 for the $25,000 you borrowed. If it's seven years, the same two numbers mean about 17.6% and $43,680. Same payment, same amount, roughly twice the cost.

That gap is the whole problem with being quoted a monthly payment. Until you know how many payments there are, “$520 a month” describes a competitive loan and a bad one equally well. Here is every plausible term for those numbers, and what each one would actually mean.

Why the term is the number that decides it

A loan has four moving parts: how much you borrow, the rate, how long you take, and the payment. Fix any three and the fourth is arithmetic — there is no judgment left in it. The trouble is that a salesperson can hand you one of those four, hold back another, and let you assume the rest.

Stretch the term and the payment falls, which feels like a concession. It isn't. On these numbers, going from 60 months to 84 keeps your payment at $520 while the interest climbs from $6,200 to $18,680 — three times as much money, for a change that was presented to you as a favor.

If someone quotes you a monthly payment and does not volunteer the number of payments, that omission is the sales technique. Ask.

The tell that a quote doesn't add up

Look at the shorter terms in the table above. At 48 months, $520 a month totals $24,960 — less than the $25,000 you'd be borrowing. No lender gives money away, so a four-year term is impossible at that payment. Anything under 49 months is.

If you were told it's a four-year loan, one of these is true:

• The term is longer than you were told. The most common version, and the least dramatic.
• There's a balloon payment at the end. Small payments for years, then a large lump sum you may not have been told to plan for.
• The amount isn't really $25,000. Origination fees deducted up front mean you borrow $25,000 and receive less.
• Someone misspoke. Which is fine — but you now know to get it in writing.

So is 9% good?

For an unsecured personal loan, high single digits is a decent rate for a borrower with solid credit. Low teens is ordinary. Past 20% you are paying a lot for the convenience of not shopping, and past 36% you are in territory that several states cap and that Congress banned for loans to active-duty service members.

The useful move isn't to judge the number in isolation — it's to get a second one. A credit union or your own bank will quote you a rate in an afternoon, and that quote costs you nothing but does two things: it tells you whether this offer is fair, and it gives you a number to say out loud when the lender asks what it would take. The full decoder has a field for exactly this — put your own quote in and it prices both loans side by side.

One caution on rate shopping: do it inside a two-week window. Credit scoring models bundle loan inquiries made close together into a single inquiry, and inquiries less than 30 days old are ignored by the score entirely. Spread the same applications over three months and each one counts separately.

Five things to ask before you sign

1. What is the APR? Not the rate, not the payment. The APR includes fees, and they are legally required to disclose it in writing.
2. What is the total of payments? One number, and it ends most bad deals on the spot.
3. How many payments, and is the last one the same size? This is the balloon-payment question.
4. Is there a prepayment penalty, and is the interest precomputed? If interest is precomputed, paying early saves you little or nothing.
5. What happens if I'm late? The fee, the penalty rate, and whether the loan is secured by anything you own.

A legitimate lender answers all five without hesitating, because they answer them every day. Pressure to decide immediately, a refusal to put the terms in writing, or a request for an upfront “processing fee” before the money arrives are all reasons to end the call.

What the math can't tell you

The rates on this page are solved from the payment, so they capture interest but not fees. Add an origination fee and the real APR climbs above what you see here — which is exactly why the disclosed APR is the number to compare, and why the decoder has a field for fees.

It also can't tell you whether you should borrow at all. That one is yours. But it can make sure that if you do, you're agreeing to a number somebody actually showed you.