Search

# Geometric Mean

## Definition

The geometric mean is a mathematical concept often used in financial calculations to determine the average rate of return of an investment over a certain period of time. It’s a type of mean or average, which unlike the simple arithmetic mean, takes into account the compounding that occurs from period to period. Essentially, it is the n-th root of the product of n numbers (where n is the count of numbers).

### Phonetic

The phonetic pronunciation of “Geometric Mean” is: jee-oh-meh-trik meen.

## Key Takeaways

• Geometric Mean is a type of mean or average, which indicates the central tendency or typical value of a set of numbers.
• It is calculated by multiplying all the numbers in the set together, then taking the nth root (where n is the count of numbers in the set) of the result
• Geometric Mean is particularly useful in situations where you want to compare things with very different properties, and is frequently used in financial, business, or economic analysis.

## Importance

The geometric mean is important in business and finance because it provides a more accurate measure of the return on investments that have varying rates over time. It considers the compounding effect which is vital in scenarios such as portfolio returns, inflation rates, population growth, or any other growth rates over a period. By using the geometric mean, we can achieve a more realistic projection of overall return on investments or growth, compared to arithmetic averages which may overestimate returns or growth rates, given they do not consider the effect of compounding. This makes the geometric mean an essential tool in financial analysis and planning.

## Explanation

The geometric mean is a crucial mathematical concept extensively used in finance and business to accurately calculate the average rate of return over multiple time periods. It serves a vital role, given that investment returns are typically compounded, not simple, and the actual earnings are not additive. Standard arithmetic averages might not represent an accurate depiction of returns, especially when dealing with volatile investments like stocks and mutual funds. Thus, employing the geometric mean allows for a precise understanding of the compound growth rates and helps in providing a truer picture of financial performance over time.

Furthermore, the geometric mean is crucial for comparing different investment opportunities or portfolios. For example, in assessing the performance of a mutual fund over several years, the geometric mean gives a more accurate annual growth rate, capturing the reinvestment of dividends and capital gains, thus reflecting the cumulative impacts of gains and losses. It also helps in risk assessment by emphasizing negative results, as negative returns have a more substantial impact on the geometric mean than on an arithmetic one. Therefore, by using the geometric mean, investors and financial analysts can make more informed and strategically sound decisions.

## Examples

1. Investment returns: This is probably the most common real-world application of the geometric mean. Let’s say that you’re an investor and you want to calculate the average rate of return over several years. If you have an investment that appreciated by 20% in year one, 10% in year two, and 5% in year three, you would use the geometric mean to calculate the average return. The geometric mean would be the cube root of (1+0.20)*(1+0.10)*(1+0.05), minus 1, or around 11.6%.

2. Population growth: Another common application of the geometric mean is in estimations of population growth. The geometric mean is often used to calculate the average annual growth rate of a population. For example, if a town’s population grew from 10,000 to 20,000 over a decade, the geometric mean could be used to calculate the average growth rate per year.

3. Business Statistics: The business world often uses geometric mean to compute changes in sales, revenues, and other figures over time. The geometric mean offers a more accurate reflection of the overall pattern. For example, if a business had sales of \$100,000 in year one, \$120,000 in year two, and \$150,000 in year three, the geometric mean would provide the average growth rate per year.

What is a geometric mean?

The geometric mean is a type of average that indicates the central tendency or typical value of a set of numbers through the product of their values. It is often used in finance and other areas of mathematic where percentages and exponential growth is involved.

How is the geometric mean calculated?

The geometric mean is calculated by multiplying all the numbers together, then taking the nth root of that product, where n is the total count of numbers.

Why is geometric mean used in finance?

The geometric mean is particularly useful in finance because it can help accurately calculate long-term investment returns, account for volatility, and illustrate the impact of compounding.

What is the difference between geometric mean and arithmetic mean?

The arithmetic mean is simply the sum of all numbers divided by the count of numbers, while the geometric mean uses multiplication and roots. The geometric mean is typically less than or equal to the arithmetic mean.

Is the geometric mean always the best choice for calculating averages in finance?

Not necessarily. While the geometric mean is great for reflecting the compounding effect in long-term investments, it might not be the best choice for all financial computations. Understand the nature of your data before choosing which type of mean to use.

How does volatility affect the geometric mean of an investment?

Geometric mean takes into account volatility. Higher volatility will result in a lower geometric mean as compared to the arithmetic mean. Hence, it’s a more realistic measure of long term investment performance.

Can negative numbers be used in the geometric mean?

No. The geometric mean requires all the numbers to be positive because you can’t take the root of a negative number in the real number system.

## Related Finance Terms

• Exponential Growth
• Mathematical Statistics
• Return on Investment (ROI)
• Compounded Interest
• Annualized Rate of Return

At Due, we are dedicated to providing simple money and retirement advice that can make a big impact in your life. Our team closely follows market shifts and deeply understands how to build REAL wealth. All of our articles undergo thorough editing and review by financial experts, ensuring you get reliable and credible money advice.

We partner with leading publications, such as Nasdaq, The Globe and Mail, Entrepreneur, and more, to provide insights on retirement, current markets, and more.

View our editorial process

Our journalists are not just trusted, certified financial advisers. They are experienced and leading influencers in the financial realm, trusted by millions to provide advice about money. We handpick the best of the best, so you get advice from real experts. Our goal is to educate and inform, NOT to be a ‘stock-picker’ or ‘market-caller.’

Why listen to what we have to say?

While Due does not know how to predict the market in the short-term, our team of experts DOES know how you can make smart financial decisions to plan for retirement in the long-term.

View our expert review board