401(k)s can offer many options for investment, but they generally only offer 15 or fewer in each plan.

Investment options in your 401(k) are completely determined by the agreement between your employer and the custodian. Therefore, you’re limited to the investment instruments selected for you.

The majority of 401(k) plans will offer fewer than 15 investment options, which are generally part of prepackaged 401(k) products from major broker-dealers or mutual fund companies. Large companies will frequently also offer stock of their company within the 401(k) plan architecture.

It is also common to see fixed accounts with guaranteed rates of return as an option, in addition to a liquid money market account option. Beyond that the most common investment options available inside 401(k)s are mutual funds, which usually include a few options for various risk tolerances and time horizons, such as allocation funds, and increasingly popular target-date funds.

Lately, it has also become more popular to offer Open Architecture 401(k)s, in which an investment advisor helps an employer construct a plan using a custodian, a bookkeeper, and a third-party administrator, to offer a custom-selected mix of investment options, which could be quite expansive.

There are also companies who will serve as trustee of various assets such as real estate holdings and thereby make it possible to hold various assets inside of a 401(k) that could not previously exist there. Such plans are known as Self-Directed 401(k)s, and they normally use open architecture like the plans described above. There are also Self-Directed IRAs.