The interest rate is the cost of borrowing the principal alone. The Annual Percentage Rate (APR) is the interest rate plus most of the fees the lender charges, expressed as a single annualized percentage. APR is almost always higher than the interest rate, and it is the number to use when comparing loan offers because it captures the full cost of the loan in one figure.

The Truth in Lending Act mandate. The Truth in Lending Act (TILA), 15 U.S.C. § 1601 et seq., and Regulation Z (12 CFR § 1026) require lenders to disclose APR for most consumer credit. The point is to make loan comparisons honest by including the fees that lenders might otherwise hide in the interest rate. Without APR, a lender could advertise a 4% interest rate but charge $4,000 in fees on a $100,000 loan, making the real cost similar to a 5% rate with no fees.

What APR includes. The exact list varies by product type, but typically:

For mortgages: interest rate, origination fees, discount points, mortgage insurance premiums, and certain closing costs. Excluded: title insurance, appraisal, credit report, and some third-party fees in most cases (though specific inclusions are governed by Reg Z).

For personal and auto loans: interest rate, origination fees, and any required loan-related charges. Some lenders bundle administrative fees into the financed amount and disclose APR accordingly.

For credit cards: APR is essentially equal to the interest rate because most credit card fees (annual fee, late fees, foreign transaction fees) are not included in APR under Reg Z's specific credit card rules. The card APR you see is the periodic rate annualized, and it is what gets applied to your balance if you carry one.

The math difference, with an example. A $300,000 30-year mortgage at 6.5% interest has a monthly principal-and-interest payment of about $1,896. Add $5,000 in upfront fees, and the APR rises to about 6.65%. The interest rate (the rate applied to the unpaid principal each month) stays 6.5%. The APR (which spreads the upfront fees over the loan term) rises to 6.65%. APR is the better number to compare across lenders because the lender with the lower interest rate but higher fees may not be cheaper overall.

Why APR can mislead even though it is more honest.

1. Time horizon. APR amortizes upfront fees over the full loan term. If you sell or refinance the home in 5 years on a 30-year loan, the actual effective cost was higher than the APR suggested because the fees were amortized over fewer years than the calculation assumed.

2. Variable rates. APR on a variable-rate loan is calculated at the current rate. If the rate rises, your actual cost rises too, and the APR you saw at origination becomes less informative.

3. Different fee inclusions across products. Mortgage APR includes some fees but not others. Credit card APR includes almost no fees. Auto loan APR depends on the lender's fee structure. Cross-product APR comparisons (mortgage versus personal loan) are harder than they look because the calculation conventions differ.

4. APR rules are different for different products. The Truth in Lending Act applies different APR-calculation rules for closed-end credit (mortgages, auto loans, personal loans) versus open-end credit (credit cards, HELOCs). Comparing a mortgage APR to a credit card APR is not apples-to-apples.

The simple rule. Within the same product type, comparing two lenders' APR numbers gives you a true cost comparison. The lender with the lower APR is cheaper assuming you hold the loan for the full term and the rate is fixed. If you might refinance, sell, or pay off early, weight the loan with lower upfront fees more heavily, even if its APR is slightly higher.

The credit card-specific rule. Credit card APR is the rate applied to balances if you carry them. If you pay your statement balance in full each month, the APR rarely matters; you do not pay interest. The APR matters only when you revolve. Credit card minimums and the way interest compounds (typically daily) can make even a moderate APR (15% to 22%) extremely expensive over time. See our piece how scary is credit card debt actually if I am only making minimum payments?

Variable APR versus fixed APR. Fixed APR stays the same for the life of the loan (or the life of a credit card account, subject to certain notice requirements). Variable APR is tied to an index (typically the prime rate or SOFR) plus a margin. If the index moves, your variable APR moves with it. Most credit cards are variable. Most personal loans are fixed. Mortgages can be either; ARMs are variable, conventional 30-year loans are fixed.

Penalty APR. Some credit cards apply a penalty APR (typically 29.99%) if you make a late payment. The Credit CARD Act of 2009 limits when penalty APRs can be applied to existing balances. Penalty APRs apply to new charges and, after 60 days of nonpayment, can be applied to existing balances.

Promotional APR. 0% APR balance transfer or purchase offers run for 6 to 21 months typically, then convert to the standard APR. Read the fine print; if you carry any balance into the regular-APR period, the issuer typically applies the new rate to the entire remaining balance from the first day of the promotional period (back-billed interest). The Credit CARD Act prohibits some forms of back-billing on legitimate promotional offers, but "deferred interest" promotions (common with retail store financing for furniture, appliances, healthcare) often retroactively charge interest from day one if not paid in full by the promotion's end.

Interest rate is the cost of the principal. APR is interest plus most fees, expressed as one annual number. Use APR to compare loans within the same product type, and don't carry a credit card balance if you can avoid it.