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What Is the Optimal Size of the Mutual Fund Portfolio?

A mutual fund usually has a great potential to grow fast. While investors keep flocking to it, the size can turn into a mammoth size. The question is if there is a possibility for the mutual fund to grow so big that it can be to the detriment of its performance.


Experienced investors generally try to determine if the fund is too large or too small before entering. It will give a clear understanding of real fund value as well as if it is worth investing in.

In this article, we will try to identify the optimal size of mutual funds without using a mutual fund calculator. You will learn how to determine the pool of assets that fits your investment goals and preferences.

What Is a Mutual Fund?

It is a pool of assets bought by a team of investors. They cooperate while purchasing and managing different instruments including stocks, bonds, securities, etc. The main idea of such a partnership is to create an as diverse portfolio as possible to fit everyone in the pool.

Generally, mutual funds are managed by professional fund managers while everyone can become an investor despite financial background or trading skills.

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How Mutual Funds Grow

When we speak of the mutual fund size, we generally mean the total volume of assets involved. Oppositely, we can consider the total amount of money invested in all available assets.

While open-ended funds are the most popular with investors today, they have two baseline ways to ensure potential growth:

  1. The first opportunity to grow is determined by the strengthening performance of assets included in the portfolio (stocks, securities, bonds, etc.). If the price of the asset is growing, the fund also comes with an increased value.
  2. The second growing opportunity is backed by the cash inflow. The more money investors get into the fund, the stronger and bigger-sized it will become. In simpler words, the portfolio can be weak and have a negative return. However, the size of assets can continue growing while investors are pouring money into the mutual fund.

Both options coexist. One leads to another. A mutual fund with a healthy and strong portfolio will attract new investors.

Big Mutual Fund Size Can Hinder Performance

The more investors are brought in, the more cash to manage by the fund manager. It creates additional pressure that can hinder the fund’s performance. The key challenge here is to put all the money at work as fast as possible. At the same time, selecting the asset to invest in requires analysis and research.

In simpler words, there is a risk of selecting the wrong asset or an instrument that will not be the right fit. This is why it is very important to find properly-sized mutual funds to invest in. You will hardly find a ready-to-use formula or a mutual fund calculator to determine the optimal size. However, specific conditions will make it clear if the underlying fund can be a good match.

When the Mutual Fund Size Does Not Matter

The size of the fund will hardly be a problem if the main assets involved are bond and index funds. What’s more, the bigger the fund the better on this particular occasion. The big size minimizes the chance of investment missteps.

When the Mutual Fund Size Matters

On some occasions, oversized mutual funds can mismatch the investment style. Imagine a small-cap growth fund with mutual assets rising from $100 million to $1 billion. Fund managers will not be able to maintain this enormous cash inflow, which means the fund performance is no longer effective.

Oppositely, small-cap funds are specialized in managing thinly traded assets (mainly stocks). Too much money will mean extra troubles and challenges for the fund manager. Again, it results in ineffective money and asset management.

Ways to Manage Mutual Fund Size Difficulties

When a mutual fund grows too big and starts compromising the manager’s ability to make well-thought investment decisions, there are 3 major options to improve the situation:

  • Use the same strategy and adapt it to a bigger amount of funds.
  • Change the investment style and strategies.
  • Keep the mutual fund closed to new investors.

How to Find a Mutual Fund of Matching Size?

To find a fund that meets your expectations, you can use the following rules. They can help you determine if the fund size improves the overall performance to investors’ benefit or hinders it:

  • Take into account the fund size in connection with the investment approach. As stated earlier, small-cap funds should not be too big, while bond and index-oriented funds have no problem with being oversized.
  • Do not invest in funds with shrinking assets. When we say “shrinking assets” we mean instruments with a negative return. In simpler words, the fund is losing money or underperforming.
  • Be careful with mutual funds that have huge holdings in cash. Generally, funds do have to keep a small amount of cash as a reserve. However, it should never exceed 15%. Otherwise, it is a sign of a fund manager having difficulties with maintaining the cash flow.

The Bottom Line

Mutual funds tend to grow over time. Sometimes, it leads to underperformance or investment missteps. So, investors should select the best mutual fund to invest in thoroughly. They need to consider the amount of reserved cash, trading style and approach, as well as a selection of targeted assets.

This material does not contain and should not be construed as containing investment advice, investment recommendations, an offer of or solicitation for any transactions in financial instruments. Before making any investment decisions, you should seek advice from independent financial advisors to ensure you understand the risks.