What Annual Percentage Yield Depends On

The interest rate is the most critical dependency for calculating the annual percentage yield (APY), as it directly affects the yield and a rate of 0% would result in an APY of 0%, rendering savings accounts or investments unattractive, like the Japanese experience with near-zero interest rates from 1999 to 2005, which led to a decline in savings rates.

Key Dependencies

• Compounding frequency — the frequency at which interest is compounded affects the APY, and without it, the yield would be lower, for example, daily compounding results in a higher APY than annual compounding, as seen in the difference between a credit union offering daily compounding and a bank offering annual compounding, where the credit union's daily compounding results in a 5.12% APY versus the bank's 5.00% APY.
• Principal amount — the initial amount of money deposited or invested is necessary to calculate the APY, and without it, the yield cannot be determined, as illustrated by the failure of the Madoff investment scheme, where the lack of a verifiable principal amount led to a Ponzi scheme that eventually collapsed.
• Time — the duration for which the money is deposited or invested is crucial in calculating the APY, and without it, the yield would be uncertain, as seen in the case of a 1-year CD versus a 5-year CD, where the longer time horizon results in a higher APY.
• Fees and charges — any fees or charges associated with the account or investment can reduce the APY, and neglecting them would result in an inaccurate yield, for example, a bank's maintenance fees can reduce the APY of a savings account, as experienced by customers of Bank of America who were charged $12 monthly maintenance fees.
• Risk level — the level of risk associated with the investment affects the APY, and ignoring it would lead to unexpected losses, as seen in the case of the 2008 financial crisis, where investments in subprime mortgages resulted in significant losses due to their high-risk nature.

Priority Order

The dependencies can be ranked in the following order from most to least critical:

• Interest rate, as it has the most significant impact on the APY, and a change in the interest rate can result in a substantial difference in the yield, as seen in the case of a 1% increase in interest rate resulting in a 10% increase in APY.
• Compounding frequency, as it can significantly affect the APY, especially for larger principal amounts and longer time horizons, as illustrated by the difference between daily and annual compounding.
• Principal amount, as it is necessary to calculate the APY, but its impact is less significant than the interest rate and compounding frequency, as seen in the case of a $1,000 principal amount versus a $10,000 principal amount.
• Time, as it affects the APY, but its impact is less significant than the interest rate, compounding frequency, and principal amount, as illustrated by the difference between a 1-year and 5-year CD.
• Fees and charges, as they can reduce the APY, but their impact is generally less significant than the other dependencies, as seen in the case of a $10 monthly maintenance fee.
• Risk level, as it affects the APY, but its impact is often difficult to quantify and may not be as significant as the other dependencies, as seen in the case of investments in government bonds versus stocks.

Common Gaps

People often overlook the compounding frequency and fees and charges when calculating the APY, assuming that they are negligible or already accounted for, which can result in an inaccurate yield, as experienced by customers of Wells Fargo who were charged unexpected fees. Another common assumption is that the interest rate will remain constant over time, which can lead to unexpected changes in the APY, as seen in the case of the 2008 financial crisis.