History Says 1 Month Has Been the S&P 500's Most Reliable Since 1950. It's Only Weeks Away.

The Vanguard S&P 500 ETF (NYSEMKT:VOO) has had a bumpy November. The fund slid more than 4% on Thursday, Nov. 5, in a sell-off led by chipmakers and other tech shares. It then gained over 2% on Monday, Nov. 9.

Investors worried the midterm election results might slow the build-out of artificial intelligence (AI). As of this writing, the fund trades near $692, down about 4% from the 52-week high it set at $718.47.

A rocky patch going into the holidays can have investors checking the calendar for some reassurance. And here, the history is encouraging.

Since 1950, the S&P 500 (SNPINDEX:^GSPC) has ended December up in 55 of 76 years. That's a 72% hit rate, and no other month has a better one.

I counted every month from 1950 through 2025 with the index's month-end closes from Yahoo Finance, on price only, without dividends. December came first, but not by much. And its record in the past decade looks far more ordinary.

Image source: Getty Images.

December edges out November and April

Two other months are close. April and November each ended higher in 53 of 76 years, or around 70%. Over all 912 months in the record, the index climbed about 61% of the time.

September was the worst month by far. It gained in just 34 of 76 years and averaged a drop of around 0.6%, making it one of only two months (along with February) with an average decline.

Put another way, December has had around nine more up years than a typical month would have across the same stretch.

Notably, December doesn't hold the highest average gain. That goes to November, at around 1.9%. December averaged a rise of around 1.4%, which is still almost double the 0.7% or so in a typical month.

How bad can December get?

The down Decembers have been rarer, but they haven't all been mild. The index dropped around 9.2% in December 2018 -- the worst December of the 76 years I checked. It also lost about 6% in December 2002 and about 5.9% in December 2022. But 10 of the 21 losing Decembers cost the index under 2%.

Each of the three worst had something bigger going on. The year 2002 was the third straight losing year of the dot-com crash, and the index finished it down around 23%. And in both 2018 and 2022, the Federal Reserve hiked interest rates in the middle of December, on Dec. 19 and Dec. 14, respectively.

The recent record is also worse than the long-term one. The index ended December up in just six of the past 10 years. It dropped around 2.5% in December 2024 and slipped less than 0.1% in December 2025, even though it rose around 23% and 16% in those two full years.

Vanguard's fund itself, which launched in September 2010, has about the same pattern. With dividends, it was up in 11 of its 16 Decembers through 2025, with an average gain of around 0.7%. That's far below the index's long-run December average, mostly because 2018 and 2022 both came during the fund's lifetime.

December's edge is small

This year's December begins at the Nov. 30 close, a Monday around three weeks from now. The Fed, which hiked rates in September and kept them steady in October, meets again on Dec. 8-9.

Of course, a 72% record over 76 years is tough to wave away. But its payoff has arguably been modest.

In the 55 years December rose, its gain averaged around 2.9%. For all 76, the average of around 1.4% is about $140 on a $10,000 stake. And the range has run from a drop of over 9% in 2018 to a rise of around 11% in December 1991.

Does December's record change how anyone should buy an S&P 500 fund? I don't think so. Its edge over a typical month has been around 12 percentage points, and the last decade shows how fast that edge can fade.

A 61% win rate for an average month is probably the more helpful number for a buy-and-hold investor planning to own the fund for years to come.

For long-term money, I'd rather keep buying on a regular schedule, December included, than wait for it or hurry to beat it. December could easily add to its record this year, but it didn't in either of the last two.

Daniel Sparks and his clients do not have positions in any of the stocks mentioned. The Motley Fool has positions in and recommends Vanguard S&P 500 ETF. The Motley Fool has a disclosure policy.