What is AER? Your Annual Equivalent Rate Guide

When exploring savings accounts or investment options, you may come across the term Annual Equivalent Rate (AER). The AER provides a standardised way to compare interest rates across different financial products, helping you make informed decisions about your savings. 

In this guide, we’ll look into what the Annual Equivalent Rate is, its significance in calculating interest, and how it differs from stated interest rates. By the end, you'll have a clear understanding of the AER and its implications for your savings.

What Is the Annual Equivalent Rate (AER)?

The Annual Equivalent Rate, commonly known as AER, represents the estimated interest rate you would earn on your savings over the course of a year, assuming the interest is compounded and paid annually. 

It takes into account the frequency of interest payments and provides a standardised measure to compare different savings accounts or investment products on an equal footing. Interest rates explained here.

How is AER calculated with monthly compounding interest?

When it comes to calculating the Annual Equivalent Rate (AER) with monthly compounding interest, it’s important to know the formula that’s used to calculate this. 

AER =[(1 + (Monthly Interest Rate))^12] - 1

Here’s a breakdown of calculating AER with compounding interest formula: 

Monthly Interest Rate: This is the nominal interest rate offered by the account, expressed as a decimal and divided by 12 (since there are 12 months in a year).

(1 + Monthly Interest Rate): This represents the factor by which your money grows each month. It's 1 plus the monthly interest rate.

^12: This exponent represents the number of compounding periods in a year (12 months).

- 1: Finally, subtracting 1 from the result gives you the AER, which is the annualised rate that takes into account the effect of monthly compounding.

Using this formula, you can calculate the AER for an account with monthly compounding interest and compare it to other accounts with different compounding frequencies to make more informed decisions about your savings.

How does AER work?

For this example, imagine if you want to deposit £10,000 into a savings account. Account A offers an interest rate of 3.9% paid monthly, whilst account B offers 4% interest paid annually. 

Account A (3.9% interest paid monthly with compounding):

Calculate the AER for Account A:

• AER accounts for the effect of monthly compounding.
• Using the formula: AER = [(1 + Monthly Interest Rate)^12] - 1
• AER for Account A is approximately 4.01%.

Interest earned in one year with Account A:

With a £10,000 deposit, you'd earn around £401 in interest over one year.

Account B (4% interest paid annually):

Since the interest is paid annually for Account B, the AER is equal to the nominal interest rate.

Interest earned in one year with Account B:

With a £10,000 deposit, you'd earn £400 in interest over one year.

Comparison:

• Account A has an AER of approximately 4.01% due to monthly compounding, and you'd earn around £401 in interest over one year.
• Account B offers a flat 4% interest rate, and you'd earn £400 in interest over one year.

In summary, even though Account A has a slightly lower nominal interest rate (3.9% monthly with compounding), its AER is slightly higher due to the effect of monthly compounding, resulting in competitive earnings compared to Account B, which offers a higher flat annual interest rate (4%). Check best interest rates for savings accounts.

Annual Equivalent Rate vs. Stated Interest

The AER differs from the stated interest rate in that it takes into account the frequency of compounding. 

While the stated interest rate only represents the interest percentage applied to your principal amount, the AER considers the compounding effect and provides a more accurate reflection of the potential returns on your savings.

Advantages and Disadvantages of the AER

AER offers several advantages:

• Comparability: The AER provides a standardised measure that allows you to compare different savings accounts or investment products on an equal footing, considering the compounding effect.
• Accurate interest calculation: By using the AER, you can estimate the actual returns on your savings over the course of a year, taking into account how often interest is added to your account.‍
• Informed decision-making: With the AER, you can make more informed decisions about where to allocate your savings, as it provides a clearer picture of the potential growth of your money.

However, it's important to be aware of potential limitations:

• Varied compounding periods: Different financial institutions may compound interest at different frequencies, making it crucial to compare AERs for accurate comparisons.‍
• Changing interest rates: The AER assumes that interest rates remain constant over the year, which may not be the case. It's essential to consider the impact of potential interest rate fluctuations on your returns.

AER Summary

The Annual Equivalent Rate (AER) is a vital tool for accurately comparing interest rates on savings accounts and investment products. By understanding the AER and its significance in calculating interest, you can make more informed decisions about where to grow your savings. 

Remember to consider the AER alongside other factors such as account terms, compounding periods, and potential interest rate fluctuations when evaluating your savings options. See Chip savings accounts.