APR vs. Interest Rate: How Regulation Z Changes the Math

When you shop a mortgage, you see two numbers side by side: the interest rate and the APR. They're rarely the same, and the gap between them isn't a mistake or a sales trick — it's the result of a specific federal formula. Regulation Z, the rule that implements the Truth in Lending Act, defines the APR as a measure of the cost of credit, expressed as a yearly rate, that relates the amount and timing of value you receive to the amount and timing of your payments. Here's how that calculation actually works, using a hypothetical example with numbers you can follow.

What Regulation Z says APR actually measures

Under 12 CFR 1026.22(a)(1), the annual percentage rate is defined as a measure of the cost of credit, expressed as a yearly rate, that relates the amount and timing of value you actually receive to the amount and timing of the payments you make. Cornell Law School's Legal Information Institute publishes the identical regulatory text, so you can check the same wording from a second source if you want to verify it. The key phrase is *value received* — not the loan amount on paper, but what you actually get to use after certain closing costs are subtracted. That's the entire reason APR and the note rate diverge: the interest rate is calculated only against the full loan balance, while the APR is calculated against a smaller, adjusted amount once specific finance charges are backed out.

Interest rate versus APR: what each one is doing

The APR, by contrast, is a measure of the cost of credit, expressed as a yearly rate, that relates the amount and timing of value you receive to the amount and timing of the payments you make. That definition comes straight from the regulatory text, which Cornell Law School's Legal Information Institute mirrors word for word.

Where to find each number on your Loan Estimate

Number	Where it appears	What it reflects
Interest rate	Page 1, under "Loan Terms"	The rate applied to your loan balance to calculate principal and interest
APR	Page 3, under "Comparisons"	The yearly cost of credit measured against the amount financed after finance charges are subtracted

Loan Estimate page references for a mortgage borrower who has received a Loan Estimate.

Worked example: a $400,000 mortgage at 6.5%

For illustration, HLJ assumes a hypothetical $400,000, 30-year fixed-rate mortgage with a stated note rate of 6.5%, where the borrower pays one discount point ($4,000) plus a $2,000 origination fee at closing. Both the point and the origination fee count as Regulation Z finance charges in this example, which matters because finance charges are what get subtracted when calculating APR. Using the standard fixed-rate amortization formula, that $400,000 balance at a 6.5% annual note rate over 360 monthly payments produces a principal-and-interest payment of about $2,528.27 per month.

• L: 400000
• i: 0.0054166667
• n: 360
• Formula: L*i/(1-(1+i)^(-n))
• Result: 2528.27

Why the amount financed shrinks

After subtracting the $4,000 point and $2,000 origination fee — a combined $6,000 in finance charges — from the $400,000 loan, the amount financed for APR purposes drops to $394,000. You're still borrowing $400,000 and still paying about $2,528.27 a month in principal and interest based on the 6.5% note rate, with no escrow, insurance or other non-finance-charge costs included in that figure, but for APR purposes, regulators treat you as effectively receiving only $394,000 in usable loan proceeds. This illustrates the amount component of what 1026.22(a)(1) means by relating the *amount and timing of value received* to the *amount and timing of payments made*.

• L: 400000
• finance charges: 6000
• Formula: L-finance charges
• Result: 394000

Key takeaways

• The APR calculates a yearly cost of credit by relating the amount and timing of value you receive to the amount and timing of your payments, per 12 CFR 1026.22(a)(1).
• If you've applied for a mortgage and received a Loan Estimate, the interest rate sits on page 1 under "Loan Terms" and the APR sits on page 3 under "Comparisons".
• In HLJ's illustrative $400,000 example at a 6.5% note rate, one point plus an origination fee — both counted here as Regulation Z finance charges — reduced the amount financed for APR purposes to $394,000, even though the principal-and-interest payment — assuming no escrow, insurance or other non-finance-charge costs — stayed at about $2,528.27 a month.

Where exactly can I find both numbers on my paperwork?

If you've received a Loan Estimate, the interest rate is on page 1 under "Loan Terms," and the APR is on page 3 under "Comparisons".

Does paying points always raise my APR compared to my interest rate?

This could not be confirmed as a general rule; in HLJ's hypothetical, the borrower pays one point ($4,000) plus a $2,000 origination fee, both treated as finance charges, and you can check your own Loan Estimate's page 1 and page 3 figures to see how your own points and fees affect the gap.

What counts as a finance charge under Regulation Z in this example?

In HLJ's hypothetical, both the one discount point ($4,000) and the $2,000 origination fee are treated as finance charges, which is why both get subtracted when calculating the amount financed for APR purposes in this illustration.

Does the monthly payment change because of how APR is calculated?

No — in the example, the monthly principal-and-interest payment is about $2,528.27 regardless of how APR is calculated, since that payment is based on the $400,000 loan amount and 6.5% note rate, not on the reduced amount financed used for APR.

Sources

• www.consumerfinance.gov
• www.ecfr.gov
• www.law.cornell.edu