No, Boomers Are Not About to Crash the S&P 500

The claim

Short version making the rounds on Instagram: 401(k) contributions from baby boomers were the main driver of S&P 500 passive indexing. Now that boomers are retiring, they're going to pull their money out and the bull market ends.

I've seen versions of this argument for 15 years. It's half-true and half-cliff-mongering. Let me lay out what's right, what's wrong, and what's actually dangerous -- in order.

What's right

Boomers have enormous assets. They control roughly $85 trillion in wealth -- about half of everything Americans own. Roughly $20 trillion sits in tax-deferred accounts between boomers and the Silent generation. The average boomer 401(k) balance is about $249,000, and mass-affluent boomer households hold multiples of that across IRAs and taxable brokerage.

The retirement wave is real. The youngest boomers (born 1964) turn 62 this year; the oldest (born 1946) turned 80. Demographic math. No argument from me.

Where the claim breaks

Three places.

First: passive flows aren't a boomer channel. Total US retirement assets are $45.8 trillion per ICI Q3 2025 data. Boomer 401(k)s are a meaningful slice, not the whole picture. The real passive flow pipeline runs through target-date-fund defaults (~$4T in TDFs, mostly held by Millennials and Gen X), IRAs ($15T+), taxable index investing led by Millennials, institutional pensions, sovereigns, and -- critically -- corporate buybacks. Boomers are one buyer pool, not the buyer pool.

Second: boomer withdrawals have been running for five years. Required Minimum Distributions under SECURE 2.0 start at age 73. The 1946 cohort hit 73 in 2019. The 1947 cohort in 2020. We have been watching boomer RMDs live, through the current bull run, at all-time highs. The S&P 500 more than doubled while RMDs were being drawn down. If the demographic cliff were real, it would already be showing up. It isn't.

Third: RMDs aren't forced liquidations. The RMD at 73 is ~3.7% of account balance. That is not retire and sell everything. You take the required distribution in cash or in-kind, redeploy to a taxable brokerage, reinvest, bequeath, or spend. The IRS doesn't force you out of equities. Many retirees stay 50-70% equity because they're planning for 20+ year retirement horizons. And the Great Wealth Transfer -- estimated at ~$84 trillion over 20 years, per CIO magazine -- is mostly intra-market flow. Boomers die, heirs inherit, most of the money stays in equities because Gen X and Millennials are now 40-60 years old and still need the growth.

The academic answer

The GAO published a study specifically on this question. Looking at 1948-2004, demographic variables explained between 1 percent and 8 percent of annual stock return variation. That is not a cliff. It's a rounding error against monetary policy, earnings, and liquidity regimes.

The boomer selling crashes the market thesis has been tested through multiple cohort generations -- Silent retirement, early boomer retirement -- and it hasn't produced the structural drag its proponents keep predicting. Demographics matter. They matter as a slow tide, not a wave. Every time someone sells you the demographic cliff, they're selling you a narrative that doesn't survive the historical record.

Where the video is accidentally right

Here is the steelman. Passive flows -- from whatever source -- are price-insensitive. They buy at any price on the way up and sell at any price on the way down. If a bear-market trigger coincides with net outflows from retirement accounts (for any reason, not just demographics), passive selling amplifies the move. That's a real risk.

But the risk isn't demographics. It's flow structure. And the actual things that break passive aren't retirement withdrawals -- they're corporate buyback cuts during recessions, target-date-fund glidepaths firing as Gen X ages through the de-risking bracket, and Mag 7 concentration unwinding.

The full piece on what actually does break passive is coming next. For now: if you saw the Instagram video and felt scared about your S&P 500 index fund, the fear is misplaced. The risk is real but the story is wrong. Watch buybacks and flow structure, not AARP membership.

My position

The next bear market will not be demographic. I'll put a number on it: if boomers-retiring-cause-SPX-crash is the mechanism, the S&P should have underperformed equal-weight indices meaningfully over the past five years as peak RMD selling ramped. It hasn't. SPX has outperformed equal-weight by roughly 30 percentage points since 2019, driven by Mag 7 concentration -- the exact opposite of what a demographic selling pressure story would produce.

The data disagrees with the video. I'll side with the data.