The backbone of anythree-fund portfoliois a U.S. stock market index fund. The two most common stock funds are the S&P 500 and the Total Stock Market index fund. These are both excellent choices, but at some point, you need to pick one or the other. So which one should you choose?

Lets look at the tale of the tape between these two indices, using the Vanguard ETF for the S&P 500 (VOO) and the Total Stock Market (VTI) as proxies:

[Data: Morningstar,VanguardStandard & PoorsCRSP]

And here are the recent historical returns of theS&P 500andTotal Stock Market index, as of January 4, 2019:

The correlation in returns between the S&P 500 and the Total Stock Market Index is very, very high. Using thiscorrelation calculator by BuyUpside, the correlation between VTI (Vanguards Total Stock Market ETF), and VOO (Vanguards S&P 500 ETF) is 99.96%. This is because approximately 75% of the total stock market portfolio is the S&P 500, and U.S. small cap stocks have a high correlation with U.S. large-cap stocks.

For comparison, the correlation between VTI and EFA (an International Developed Stock Markets ETF) was 83.4%, and the correlation between VTI and AGG (a total bond index ETF) was 83.4%. The diversification benefits of the Total Stock Market index over the S&P 500 are relatively limited.

Even experienced, well-educated index fund investors will often try tocompare their portfolios to the S&P 500. The competitive nature of investors comes out even in the index fund world, where even though youre trying to be average, some people try to seek a better average than the S&P 500. When you invest in the S&P 500, the temptation to compete against a benchmark index is eliminated.

Some investors like to overweight (tilt) their portfolios towards small cap stocks. By investing in the S&P 500, you can more cleanly tailor your large-cap and small-cap exposures to your liking. If you invest in the total stock market, then you need to account for the fact that the total stock market is approximately 73% large caps, 18% mid-caps, and 9% small-caps.

Investment aggregator services such as Personal Capital can help you sort out your large-cap and small-cap exposures, but owning specific large-cap and small-cap index funds simplifies this process.

Investing in the total stock market allows you to get mid-cap and small-cap exposure, in proportions equivalent to that of the U.S. stock market, in a single investment. Many investors have no desire to tilt our portfolios towards small-cap stocks.

In the past 15 years, the total stock market has had slightly higher long-term returns because of its mid-cap and small-cap components. However, very long-run returns of the S&P 500 and Total Stock market (1928-2010) have shown the S&P 500 to have slightly higher returns than the total stock market (10.4% vs. 10.2%), as noted by Jack Bogle inthis article. So no one really knows whether the S&P 500 or Total Stock Market will have better returns in the next 30 years.

Columnist Allan Roth also notes a potential advantage of the total stock market thathe terms the Google effect.Typically, changes in the composition of the S&P 500 are made after-hours. When these changes happen, companies that are added to the S&P 500 rise and companies that are subtracted fall.

For example, Google rose 7.3% in after-hours on the evening it was announced that they would be added to the S&P 500. In this case, total stock market index holders benefited from this rise, while S&P 500 index funds had to buy Google at inflated prices.

The turnover of the S&P 500 is relatively infrequent, so the erosion in returns because of this phenomenon is relatively small.

All else being equal, if I had a choice between Total Stock Market or S&P 500, I would pick the total stock market because of its diversification benefit. My wife, on the other hand, uses the S&P 500 for her investment accounts, preferring the familiarity of this index.

However, if you do not have the opportunity to purchase the total stock market in your investment account, then investing in the S&P 500 is an excellent alternative. This is the case for me, where my 403(b) and HSA do not offer total stock market index funds as investment options. I invest in the S&P 500 in these accounts with no hesitation. I do not attempt to replicate the total stock market by purchasing mid-cap or small-cap funds in other accounts.

Remember, for Fidelity and Schwab account holders, you should use the ETF versions of these index funds within taxable accounts because of the favorable tax treatment of ETFs. In tax-deferred accounts, you can use either ETFs or mutual funds. Vanguard account holders can use either the ETF or mutual fund version in any account.

How do you invest in the U.S. stock market? Do you use the S&P 500, Total Stock Market, or neither?

Personal Capitalenables you to track all of your investment accounts in one place. No more shifting between your Vanguard, Fidelity, and Schwab accounts to calculate your asset allocation or net worth.

They also offer paid wealth management services, but you can decline these and still access their free net worth calculator tools.

Sign up for a free accountand start tracking your investments today.

Forum Mailbag: Dave Ramseys Advice To Residents, Tilt Away From Healthcare, Modeling Inflation, and More!

VTSAX Review: Invest In The Largest Mutual Fund In The World

Freedom, Freedom Index, or Freedom Blend: Understanding Fidelitys Confusing Lineup Of Target-Date Funds

I tend to prefer s and p 500 and a small cap over total stock market. Because of the index being market cap weighted in order to get mid and small caps in the proportions I prefer I need an index specifically for small caps. As you have referenced, I tilt.

SP 500 makes sense for those who tilt their portfolios, since they want more control over their small cap vs. large cap exposure.

I had never heard of the google effect. Very interesting. I can imagine it is a rare occurrence but still interesting. Another reason not to be in an s and p fund. Especially if the goal is to set it and forget it.

Its a small effect, but the differences between the SP 500 and Total Stock Market are small.

WSP, I enjoyed reading this. Really nice summary of pros/cons.

How does both work for you? We invest in the SP500 in my 401K (VIIIX) and VTSAX in our taxable account.Mrs PIE 401K has a set of weighted funds mimicking the TSM in terms of the equities portion of it.

Like you, all based on choice of funds in each part of our portfolio. Pragmatic and works for us.

Its always interesting to hear what the leading financial whizz-kids say about VTSAX vs SP500. Taylor Larimore over at Bogleheads had a fascinating comment in this thread on the forum when discussing VTSAX vs SP500. Enjoy.

Thanks Mr. PIE. Taylor is full of wisdom, and I know he is a strong proponent of the Total Stock Market index fund as part of a three-fund portfolio.

What a great comment by Larimore there. People reference it all the time. There is just so much sleep easy-ness to the TSM. Its like, what do you have to lose unless everything goes to hell anyway?

Was about to Tweet your post and darned if I can find you in Tweet space..

Thanks for sharing! My Twitter handle is @WallStPhysician. Theres also a button at the bottom of the post where you can share the post to Twitter.

Im a TSM guy myself, but Im not going to pretend it makes a big difference.

It doesnt, but its a pretty common question from people starting out with investing and index funds.

Thanks for the write up. Ive wondered what the key differences were between the two and how these two indexes performed. But I was lazy and didnt get around to it. After reading your article, I would tip my hand toward the total stock market index.

Very nice. So would I, but other very smart people feel differently.

Great write-up WSP, thanks for sharing. Im in Vanguards Total Stock Market.

Nice, another vote for Total Stock Market. I think if I ran a poll, TSM would win, but theres nothing wrong with investing in SP 500.

Great topic, for me the changes in both are too limited to chose the S&P over the TSM, which is why I would choose the latter. More over because the biggest effect is still coming from the large caps.

Were currently invested in individual stocks, in bot mid caps and large caps, and are looking to further diversify using an ETF (or 2). Instead of finding diversification in big/small, and we dont want to be invested in US stocks only, we are checking out the global en EU indexes as well.

Ill definitely be writing a future post on which ETF / index fund to use for international stock exposure.

We use the Total market just out of simplicity, it gives us all the exposer we want in one fund.

Im also on board with using the total market, however the S&P 500 makes a nice tax loss harvesting partner if youre comfortable owning it for the long run.

Agreed the decision is not completely either/or.

I have a something in both the S&P 500 is the closest to total stock in my 401k, and in my IRAs I have total stock to keep things simple. But I definitely wouldnt have both if I was able to have a single account with a single set of investment offerings, and I would prefer total stock to get exposure to smaller companies.

This is not an uncommon scenario when there is no TSM option, buy SP 500, but when TSM is available, choose that over SP 500.

Depending on account (401k, IRA, brokerage) I pick the option with the lowest fees. When given an even chance, I go Total Market. Simple and gives a broad range, because in the end I just want to own the world 🙂

Appreciate the article and all the input. I am looking to invest some extra cash rather short term ~5 yrs in a taxable account. Leaning towards TSM. Would it make a difference vs S&P 500?

Wouldnt make a difference. I prefer TSM all else being equal.

So at the moment I have my Tax deferred account in the Vanguard 500 Admiral shares, and my taxable account in VTSAX, should I look at investing my taxable account in a fund that only has exposure to mid and small cap since the VFAIX is all large cap, or should I just leave it.

I would definitely just leave it. I assume you are in the Vanguard 500 Admiral shares because your tax-deferred account doesnt have an option for VTSAX or some other total stock market index fund. My retirement plan at work also does not have a total stock market option, so I just invest it in the SP 500 fund with no consideration of balancing it with a small-cap/mid-cap or extended market fund in a different account.

Im thinking to add vanguard etf to supplement vanguard s&p 500 VOO to approximately invest in us Total stocks. Im confused between VIOO vanguard s&p 600 small cap and VB vanguard Small Cap blend or VXF vanguard Extended Market. Any suggestions? Thanks

Subscribe to receive exclusive content and new post notifications.

Before I went to medical school, I worked on Wall Street as a trader at an investment bank. Now I am a physician helping fellow doctors navigate the crazy world of finance.

Personal Capitalenables you to track all of your investment accounts in one place. No more shifting between your Vanguard, Fidelity, and Schwab accounts to calculate your asset allocation or net worth.

They also offer paid wealth management services, but you can decline these and still access their free fee analyzer or net worth calculator tools.

Sign up for a free accountand start tracking your investments today.

If you are a resident, fellow, or doctor fresh out of training, come join theWall Street Resident Physicians Facebook group. I want to make it the best place for physicians-in-training to talk personal finance and investing with other residents and fellows.

I am a doctor, not an accountant or financial advisor. Please consult your tax advisor or financial professional before making any investment or personal finance decisions.

Posts and pages on this website contain affiliate links that help keep the Wall Street Physicians lights on. Thanks for your support of the blog!