Reddit’s S&P 500 debut could unleash nearly $3 billion of index-fund buying | Louis Velazquez - Official Website, Entrepreneur, Finance, Technology

Reddit (RDDT) is set to join the S&P 500 before the market opens on Aug. 18, replacing AvalonBay Communities (AVB).

J.P. Morgan analysts estimate index funds that track the benchmark will need to buy about 16.7 million Reddit shares to reflect the adjustment.

At Reddit’s Friday-morning price of roughly $175.69, that’s close to $2.9 billion worth of stock.

That is a lot of potential flow for a business that has had an average daily trading volume since its March 2024 IPO of approximately 5.98 million shares. This means that the projected demand for the index fund is about three times the typical daily volume of Reddit.

Shares surged more than 11% on the announcement.

This scenario is a strange setup for investors. Reddit is down over 31% this year through Thursday and 42% from its all-time peak in September 2025.

Now, after months of decline, a set of investors may suddenly have to buy the stock whether they love the fundamentals or not.

The next several trading sessions are less about opinion and more about mechanics.

Reddit’s S&P 500 inclusion creates a powerful technical catalyst

Trillions of dollars of passive and benchmark-aware assets follow the S&P 500.

When a firm joins the index, funds that track it must rebalance their portfolios. This behavior tends to lead to predicted buying pressure in advance of the effective inclusion date.

The magnitude of this buying pressure is what’s impressive for Reddit.

J.P. Morgan’s estimate of 16.7 million necessary shares translates to nearly three days of average trading volume in a somewhat tight rebalancing timeframe.

That helps explain why investors flocked to the shares right after the announcement.

A conventional rally usually begins with a change in the business. Revenue beats estimates. Margins grow. An analyst upgrades a target. A new product offers some hope.

An index-inclusion rally is different.

The stock can go up since demand is set to mechanically increase.

An S&P 500 index fund can’t be the one to say that Reddit looks costly and pass on the buy. Its job is to follow the benchmark as closely as possible.

That creates a unique situation where investors can at least roughly anticipate how much new demand may be on the way.

That demand is about $3 billion at around $175 a share.

And that can make for an especially severe shift for a stock that’s already been knocked down hard from its highs.

Reddit’s new buyers are arriving after a brutal year

But the timing is what makes the narrative more interesting.

Reddit is not joining the S&P 500 after a clean, continuous rally.

The stock was down more than 31% in 2026 through Thursday and down more than 42% from its record high last September.

That suggests index funds are ready to buy after a big drawdown.

Still, questions remain for the business itself.

In its most recent quarterly earnings report, Reddit stated that erratic search-engine traffic in the second quarter impacted U.S. user growth. That flaw obscured a bright revenue outlook elsewhere.

So the S&P 500 catalyst doesn’t eliminate the fundamental Reddit argument.

It’s a temporary shift in the equation of supply and demand surrounding the stock.

This distinction is important.

That is to say, a corporation can have a lot of index buying and little change in the fundamental performance of the operations.

The challenge for investors who want to join the rally is whether the mechanical demand will offer enduring support after the rebalance is over.

Steve Huffman watches as Reddit begins trading on New York Stock Exchange.

Spencer Platt / Getty Images

History suggests the biggest Reddit move could come before inclusion

Another wrinkle.

Stephens analyst Melissa Roberts said newly added S&P 500 companies have historically outperformed the benchmark between the announcement and the actual inclusion date.

The best profits have always been the day after the announcement.

After inclusion, however, those stocks have historically surrendered some of their gains and lagged the S&P 500 by roughly 2% over the next three months.

That pattern makes sense intuitively.

Traders know they will be buying index funds. Some investors position themselves in advance of those purchases, thus front-running the rebalance.

After the inclusion is done and the buying finished, the technological catalyst is gone.

Then the stock is re-evaluated on its business performance, valuation, and what investors are expecting.

That implies the next few days at Reddit may be driven by very different dynamics than the following few months.

More Wall Street:

Reddit shareholders therefore have two stories to watch at the same time.

The first is mechanical: how much buying truly takes place when index funds rebalance?

The second is a biggie: Can Reddit fix its U.S. user growth and continue to convert its large audience into sustainable revenue?

The first one may move the stock swiftly.

The second will decide where it finally ends up.

Why Reddit is getting the S&P 500 spot

Reddit is entering the benchmark because AvalonBay is being removed following its agreement to merge with Equity Residential (EQR).

The firms announced in May an all-stock deal that would establish a rental-housing company with an enterprise value of around $69 billion.

The combined business, which will be called Vivmark Residential, is expected to remain in the S&P 500 after the merger closes.

That creates an opportunity for Reddit.

The inclusion marks a major milestone for a company that went public just in March 2024.

In just over two years, Reddit has transformed from an IPO newcomer to one of the 500 firms listed in the most-watched U.S. equity benchmark.

Reddit investors now face a very different short-term setup

The numbers make the near-term trade easy to understand.

Reddit’s S&P 500 numbers

16.7 million shares: J.P. Morgan’s estimate of what S&P 500 index funds may need to buy.
$175.69: Reddit’s approximate Friday-morning share price cited by Reuters.
Nearly $2.9 billion: Approximate value of that potential index buying.
5.98 million shares: Reddit’s average daily trading volume since its IPO.
11%+: Initial stock jump following the announcement.
31%+: Reddit’s 2026 decline through Thursday.
42%+: Decline from its September 2025 record high.
Aug. 18: Effective date of Reddit’s S&P 500 inclusion.

For Main Street investors, the takeaway is rather simple and straightforward.

Reddit is close to being included in one of the world’s most closely followed stock indexes, a move that may lead to funds buying roughly $3 billion of its stock.

That doesn’t mean the stock will continue to rise.

In fact, history shows some of the biggest benefits from index inclusion come before a company is added to the benchmark.

But the predicted buying is substantial enough to matter.

Reddit’s core business still needs to establish user growth, and advertising and monetization can support valuation over time.

But the stock has something far more immediate working for it over the next few days.

Millions of shares may be looking for new owners.

And many of those buyers don’t get to say no.