Vanguard Prime Money Market Fund (VMMXX)

Updated July 2, 2021

What Is a VMMXX?

The Vanguard Prime Money Market Fund, or VMMXX, is an investment fund offered through Vanguard that invests in U.S. government securities and foreign bonds.

As its main goal is to provide current income and preserve shareholders’ principal investments, the fund maintains a share price of $1. For this reason, it is considered one of the most conservative investment options offered by Vanguard. 

How Does VMMXX Work?

The fund invests in very short-term investments of less than one year to maturity, if interest rates go up (or down), the yield will also go up (or down). Barring a financial crisis, there is little risk associated with this fund.

What’s the Average Yield of VMMXX?

The fund holds $121 billion in assets (2019). The amount of income that a shareholder may receive will be largely dependent on the current interest rate environment. 


The Vanguard Federal Money Market Fund (VMFXX) and the Vanguard Prime Money Market Fund (VMMXX) are quite similar, in both purpose and composition of investments.

The VMFXX invests in short-term U.S. government bonds and obligations. It is the safest possible fund.

The VMMXX invests mostly in U.S. Treasury bills and short-term commercial paper. Either fund provides a safe investment, but with relatively low returns, reflecting its low risk.

Activate your free account to unlock our most valuable savings and money-making tips
  • 100% FREE
  • Exclusive money-making tips before we post them to the live site
  • Weekly insights and analysis from our financial experts
  • Free Report - 25 Ways to Save Hundreds on Your Monthly Expenses
  • Free Report - Eliminate Credit Card Debt with these 10 Simple Tricks
Ask an Expert
All of our content is verified for accuracy by Rachel Siegel, CFA and our team of certified financial experts. We pride ourselves on quality, research, and transparency, and we value your feedback. Below you'll find answers to some of the most common reader questions about Vanguard Prime Money Market Fund (VMMXX).
Be the first to ask a question

If you have a question about Vanguard Prime Money Market Fund (VMMXX), then please ask Rachel.

Ask a question
Rachel Siegel, CFA
CFA logo

CFA Charterholder

Chartered Financial Analyst

Rachel Siegel, CFA is one of the nation's leading experts at ensuring the accuracy of financial and economic text.  Her prestigious background includes over 10 years creating professional financial certification exams and another 20 years of college-level teaching.

If you have a question about Vanguard Prime Money Market Fund (VMMXX), then please ask Rachel.

Ask a question Read more from Rachel
Rachel Siegel, CFA - profile
Ask an Expert about Vanguard Prime Money Market Fund (VMMXX)

By submitting this form you agree with our Privacy Policy

Don't Know a Financial Term?
Search our library of 4,000+ terms