When you borrow money or deposit it into a savings account, the number you see—the interest rate—is not always the total cost or return. Financial institutions use two primary standards to communicate these figures: APR and APY.
While they look similar, their functional difference is rooted in a single concept: compounding. APR is used for loans and credit cards, whereas APY is typically used for savings accounts and certificates of deposit (CDs).
What is APR and how is it calculated for loans?
APR stands for Annual Percentage Rate. It represents the yearly cost of borrowing funds, as a percentage of the total amount. It is the standard used for products like credit cards and mortgages.
The basic APR calculation is simple:
- Daily Periodic Rate: Divide the APR by 365 (some banks use 360).
- Daily Interest: Multiply your daily balance by the periodic rate.
- Monthly Interest: Add up the daily interest amounts for the billing cycle.
On a credit card with an 18% APR, the daily periodic rate is approximately 0.049%. If you carry a $1,000 balance each day of a 30-day month, you will be charged roughly $14.70 in interest.
Why does APR include fees (sometimes)?
For mortgage products, the “Effective APR” includes more than just the interest. It incorporates mandatory costs like loan origination fees, mortgage insurance, and closing costs. This higher figure is designed to give the borrower a more accurate comparison of the total cost of the loan over its entire life.
How does APY differ from APR?
APY stands for Annual Percentage Yield. It represents the amount of interest you actually earn on a savings account over one year, accounting for compounding.
Compounding is the process of earning “interest on interest.” If you start with $1,000 and earn $10 in interest during the first month, the second month’s interest will be calculated on $1,010.
- APR reflects the “stated” rate.
- APY reflects the “real” rate after compounding.
If a savings account has a 5.00% interest rate that compounds monthly, the APY will actually be 5.12%. This is because the interest earned each month is added to the balance, increasing the amount on which future interest is calculated.
Why does the “Compounding Frequency” matter most?
The frequency of compounding—how often interest is calculated and added to the balance—is the primary driver of the difference between APR and APY.
- Daily Compounding: Provides the highest APY for a given interest rate.
- Monthly Compounding: Standard for most savings accounts and mortgages.
- Quarterly/Annual Compounding: Results in a lower APY.
For the borrower, compounding frequency isn’t always a benefit. Credit cards compound interest daily, meaning that if you carry a balance, you are being charged interest on the interest that was added to your account just 24 hours ago.
How can you quickly compare APR and APY?
When evaluating a financial product, you must ensure you are comparing “like with like.”
- Borrowing: Always look at the APR. It ensures you understand the yearly cost of the debt.
- Saving: Always look at the APY. It ensures you understand exactly how much your money will grow after a year of compounding.
A common marketing tactic is to highlight the APR for loans (which is the lower number) and the APY for savings (which is the higher number). In both cases, the institution is presenting the most attractive figure by utilizing the math of compounding to their advantage.
Understanding the mechanics of interest calculation allows you to move beyond the stated percentage and determine the actual impact of a financial decision on your net worth.
