Are We in a Market Bubble? A Closer Look at the Numbers
Dominik Yates · · 7 min read
The S&P 500's Shiller CAPE ratio sits at roughly 41 as of October 2026 — its second-highest reading in over 150 years of recorded data, surpassed only by the dot-com peak of 44.2 in late 1999. That one number has fed a wave of alarm: headlines declaring the AI bubble is bursting, analysts warning of an imminent correction, and investors quietly wondering whether they're watching history repeat itself. The honest answer is that it's more complicated than any single metric suggests — and understanding why matters more than landing on a yes or no.
Why the CAPE Ratio Looks So Alarming
The Cyclically Adjusted Price-to-Earnings ratio, developed by economist Robert Shiller, divides the S&P 500's current price by the average of its inflation-adjusted earnings over the prior ten years. That decade-long smoothing window is the metric's greatest strength — it filters out the noise of any single boom or recession year. But it's also its most important limitation in the current environment.
When earnings growth is unusually rapid, as it has been recently, that ten-year average lags behind reality. The CAPE effectively underweights the most recent earnings, which means it can overstate how expensive stocks actually are. According to the firm's research into this question, the S&P 500 saw its earnings grow by nearly 30% in a recent quarter — the third consecutive quarter of growth above 25% year-over-year. For context, the 25-year average earnings growth for the S&P 500 has been 6.4%. When current earnings are running at four times the historical pace, a metric that relies on a decade-long average will naturally make valuations look stretched even when current earnings may justify higher prices.
That doesn't make the CAPE irrelevant. It was designed precisely to see past periods of unsustainable growth, and the current growth rate almost certainly won't hold indefinitely.
The Forward PE Tells a Different Story
Shift from trailing to forward-looking metrics and the picture changes materially. The forward 12-month P/E ratio for the S&P 500 — which prices the index against consensus estimates of the next year's earnings — currently stands at 19.0, below both its 5-year average of 19.8 and its 10-year average of 19.1, according to FactSet's most recent Earnings Insight. That's not cheap in an absolute sense, but it's a very different signal than the CAPE alone conveys.
The distinction between these metrics is not a technicality. Trailing ratios look backward; forward ratios price what analysts believe companies will earn. Both carry their own forms of uncertainty. The CAPE smooths out cycles but can lag surges in earnings. Forward estimates, meanwhile, are systematically optimistic when the economy is expanding — analysts tend to overestimate, and actual results often come in below the initial forecast. Neither measure is a reliable market-timing tool on its own.
Valuation metrics are a lens, not a verdict — each one answers a slightly different question, and none of them knows what happens next.
There's also a concentration problem worth naming directly. The Magnificent Seven — Google, Amazon, Apple, Meta, Microsoft, Tesla, and Nvidia — represent roughly a third of the entire S&P 500 by weight, and their above-average valuations pull the index's aggregate multiple higher even when the other 493 constituents look more reasonably priced. When two of the most prominent AI companies, OpenAI and Anthropic, eventually come to market in their current reportedly unprofitable state, that dynamic could intensify things further.
The Equity Risk Premium: What Investors Are Actually Being Paid
One framing that cuts through the trailing-versus-forward debate is the equity risk premium — what investors earn for choosing stocks over Treasury bonds. The calculation takes the earnings yield (the inverse of the PE ratio) and subtracts the 10-year Treasury yield. When that spread narrows, investors are accepting more equity risk for a smaller marginal return over a risk-free alternative.
By this measure, the current premium is historically thin. The 10-year Treasury yield has risen meaningfully, which matters twice: it compresses the equity risk premium directly, and it acts as a gravitational force on stock valuations by pulling investor capital toward fixed income. AI-focused companies, many of which depend on continued access to external capital to fund growth, are particularly exposed to this dynamic. Rising yields raise the cost of that dependence.
A further consideration is how AI spending appears in the earnings figures investors are using to value companies. Much of the investment in chips, data centers, and infrastructure flows through capital expenditure — it lands on the balance sheet as an asset, not on the income statement as an expense. That accounting treatment flatters near-term earnings, and there are reasonable questions about whether the assumed useful life of these assets (particularly chips) is realistic. If those assumptions need to be revised, the earnings figures underpinning current valuations may be overstated.
What This Means for Long-Term Investors
The picture that emerges from looking across multiple metrics — CAPE, trailing PE, forward PE, the equity risk premium, and cross-sectional comparisons with small-cap and international indices — is neither "obvious bubble" nor "all clear." Analysts are forecasting substantial earnings growth from AI-driven productivity, and if those estimates prove roughly accurate, current valuations may have more support than the CAPE alone suggests. But a great deal of optimism is already priced in. That leaves a narrower margin for error and a real cost for investors who experience a de-rating of multiples even without an earnings decline.
International markets, for their part, are trading at considerably lower forward multiples — roughly 12–13 times — while earnings estimates for those markets are themselves rising. That gap raises natural questions about geographic diversification, though different risks (currency, geopolitical, liquidity) accompany international exposure and deserve their own careful analysis.
For investors building toward retirement or managing wealth through a complex tax and income picture, the most durable observation here is that the question "is the market in a bubble?" doesn't have a clean answer — and the confidence with which pundits deliver one, in either direction, tends to exceed what the evidence actually supports. Long-term financial plans that are constructed to withstand a range of outcomes — including periods of lower returns — tend to hold up better than ones calibrated to a specific market view. The goal is resilience, not prediction.
If questions about how current market valuations interact with your retirement income strategy or your broader financial plan are on your mind, our team is happy to work through the details with you.
Common questions
What does the CAPE ratio actually measure, and why is it so high right now?
The CAPE (Cyclically Adjusted Price-to-Earnings) ratio divides the S&P 500's current price by the average of its inflation-adjusted earnings over the trailing ten years. It stands at roughly 41 as of October 2026 — second-highest in 150 years of data — largely because stock prices have risen sharply while the ten-year earnings average is anchored to years of slower growth. The metric also lags during periods of unusually rapid earnings acceleration, which means it may currently overstate how expensive stocks are relative to what companies are actually earning today.
If the CAPE looks alarming, why does the forward PE look more moderate?
The forward PE uses analyst consensus estimates for the next 12 months of earnings rather than a decade-long historical average. According to FactSet's Earnings Insight, the forward 12-month P/E for the S&P 500 currently sits at 19.0 — below both its 5-year and 10-year averages. The two metrics answer different questions: the CAPE asks how expensive stocks are relative to long-run earnings history; the forward PE asks whether investors are paying a reasonable price for what companies are expected to earn in the near term. Neither is a reliable timing signal, and both carry meaningful uncertainty.
Should a long-term investor change their strategy based on current market valuations?
Valuation metrics can inform the context of a long-term plan, but they are generally poor short-term timing tools. Elevated valuations suggest that a portion of future expected returns may already be priced in, which is a reason for measured expectations rather than a reason to exit the market. A well-constructed financial plan accounts for the possibility of lower returns from current levels without requiring the investor to call the market's direction correctly. If current valuations are creating anxiety about your plan's durability, that's a conversation worth having with a fiduciary advisor — not a signal to act impulsively.