Every loan offer shows you two percentages that look almost the same and mean different things. One of them is the number lenders put in large print. The other is the number federal law makes them disclose, precisely because the first one is incomplete.
The interest rate: the price of the money
The interest rate is the percentage applied to your outstanding balance to calculate the interest you owe. It determines your monthly payment together with the balance and the term, and nothing else.
It is a clean, useful number. It is also the number that appears in advertising, and there is a reason for that: it is almost always the smaller of the two.
The APR: the price of the loan
The annual percentage rate takes the interest rate and folds in the finance charges you pay to get the loan — origination fees, discount points, certain closing costs — then expresses the whole cost as a single annualized percentage over the loan's full term.
The Truth in Lending Act, implemented through Regulation Z, requires lenders to disclose APR on consumer credit for exactly this reason: without it, a lender could advertise an artificially low rate and recover the difference in fees, and no borrower could compare offers.
The result is that the gap between rate and APR is itself informative. A quoted 6.50% rate with a 6.55% APR is a low-fee loan. The same 6.50% rate with a 6.95% APR is carrying thousands of dollars in up-front charges.
A worked comparison
Two lenders, same $300,000 30-year fixed mortgage. Lender A offers 6.25% with $9,000 in points and fees. Lender B offers 6.50% with $1,500 in fees.
By rate, A wins by a quarter point and it is not close. By APR, the two land far nearer each other, because A's $7,500 of extra up-front cost gets amortized across the term and shows up in the annualized figure.
Which is genuinely better depends on a fact the APR cannot know: how long you keep the loan. Hold it thirty years and A's lower rate eventually repays the up-front cost several times over. Refinance or sell in four years and you paid $7,500 to save a quarter point for forty-eight months, which is a clear loss. This is the single most important limitation of APR as a comparison tool.
Where APR breaks down
APR assumes you hold the loan to term. Most people do not hold a 30-year mortgage for 30 years, so an APR that spreads closing costs over 360 payments systematically understates their real cost to a typical borrower.
APR on adjustable-rate loans requires assumptions about future index movements that may not hold, so an ARM's APR is a projection rather than a measurement.
And APR only compares like with like. The APR of a 15-year loan and a 30-year loan are not commensurable, because the whole point of the shorter term is a completely different total-interest outcome.
Credit cards work differently
On credit cards, APR is effectively just the interest rate — annual fees, balance transfer fees, and foreign transaction fees are disclosed separately rather than baked into the number. So a card with 0% APR and a $95 annual fee is not free, and a no-fee card at 24% APR may be cheaper for someone who pays in full each month, because they never touch the rate at all.
Cards also typically carry several different APRs at once — purchases, cash advances, balance transfers, and a penalty rate — and cash advance APRs usually start accruing immediately, with no grace period.
The practical rule
Compare same-type, same-term loans by APR, then check the gap between rate and APR to see how front-loaded the costs are. If the gap is wide and you expect to move or refinance within a few years, favor the lower-fee offer even at a higher rate.
And always ask for the itemized fee list rather than reading the APR alone. APR tells you that fees exist; it does not tell you which ones are negotiable, and several of them are.