How does the Shiller CAPE differ from the forward P/E?

The short answer

The Shiller Cyclically Adjusted Price-to-Earnings ratio — known as CAPE or PE10 — divides current price by the ten-year average of inflation-adjusted earnings. Robert Shiller introduced this construction to filter the cyclical noise in single-year earnings, on the observation that profit margins mean-revert over multi-year periods. The forward P/E divides current price by analyst consensus earnings estimates for the next twelve months.

The complication is that these two measures answer different questions. CAPE asks: what is the price relative to a smoothed measure of normalised earnings power? Forward P/E asks: what is the price relative to the level of earnings the market currently expects? The first is a longer-cycle valuation anchor; the second is a near-term expectation gauge.

When the two diverge significantly — as they do now — it usually carries information. Either trailing margins are unusually elevated and CAPE is signalling regression risk, or forward estimates are unusually optimistic and the gap will close through earnings disappointment.

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What the data shows

As of May 2026, the Shiller CAPE for the S&P 500 stands at approximately 39-41, with a historical median of around 17 and a peak of 44.19 reached in December 1999. The forward P/E, by contrast, stands at approximately 22 — elevated relative to its long-term average of around 15-16 but well below 1999 readings of 25+.

This pattern of divergence is itself historically informative. The two measures aligned closely in 1982, when both were depressed at similar low multiples. They aligned again in 1999, both at extreme highs. But they diverge in the current cycle: the Shiller CAPE indicates valuation comparable to 1999, while the forward P/E indicates valuation more comparable to 2007 or 2017.

The divergence is largely explained by elevated profit margins. The S&P 500 net income margin has run at approximately 12-13% in recent years, well above the long-term average of around 8-9%. CAPE’s ten-year window incorporates the lower-margin years; forward P/E uses estimates that assume current margins persist.

→ Shiller CAPE: monthly history (dataset)

Why it happens — the macro mechanism

The mechanism connecting the two metrics runs through profit margins. Forward P/E implicitly assumes that current margins represent the new normal — that whatever has elevated margins (tax cuts, sector composition, market power, supply chain optimisation) will persist. Shiller CAPE makes no such assumption: by averaging earnings over ten years, it weights both peak and trough margin years equally, anchoring the valuation closer to a margin-cycle-neutral baseline.

Robert Shiller, in Irrational Exuberance, argued that the predictive power of valuation measures comes from their ability to filter transient effects. This is why CAPE has shown stronger correlation with subsequent ten-year real returns in academic research than single-year earnings ratios. The distance between received opinion and the figures is the topic of the assumptions that mislead investors on valuations and bubbles. But Aswath Damodaran has noted that ten-year smoothing introduces its own biases — particularly when structural changes have shifted earnings to a durably higher level, as may be the case with the rise of asset-light technology business models.

Three regime-specific patterns are visible. In the 1995-2000 regime, CAPE and forward P/E rose together because both earnings and prices were stretched by speculative tech valuation. In the 2003-2007 regime, forward P/E remained moderate while CAPE rose more, as elevated earnings from financial sector leverage flattered the forward measure. In the 2020-2026 regime, the divergence is wider than in previous cycles: CAPE near historical extremes while forward P/E remains elevated but not extreme, reflecting the durable margin elevation question.

The signature of the current regime is that both measures are elevated, but the structural questions they raise are different. CAPE asks whether margins will revert; forward P/E asks whether earnings estimates will be met.

What it means for different economic actors

For institutional asset managers, the divergence matters because forward returns may be more sensitive to which measure proves predictive. If margins revert, CAPE-based estimates of low forward returns prove correct. If margins prove durable, forward P/E-based estimates of moderate returns may better describe outcomes.

For retail investors, the practical consequence is that the choice of valuation framework shapes the perceived urgency of the situation. CAPE-anchored frameworks suggest more caution; forward P/E-anchored frameworks suggest moderate concern.

For policymakers, the divergence raises questions about the durability of corporate earnings under various scenarios — particularly tax policy changes, antitrust enforcement, or labour market shifts that could compress margins.

For households accumulating wealth, the relevant observation is that valuation matters more for multi-year planning than for next-quarter timing. Why valuations matter over the long term develops this point.

Frequently asked questions

Which metric is more reliable for long-term return forecasting?

Academic research, including work by Shiller and others, has consistently found CAPE to have stronger predictive power for ten-year forward real returns than single-year P/E ratios. The reason is methodological: by smoothing earnings, CAPE filters cyclical noise that distorts shorter-window measures. However, this predictive power applies to long-term averages — it provides little information about returns within the next twelve to twenty-four months.

Could elevated CAPE simply reflect structurally higher steady-state valuations?

This is possible. Lower trend interest rates, durable margin shifts from sector composition changes, and structural improvements in corporate efficiency could all support a higher equilibrium CAPE than historical averages. However, even adjusting for these factors using rolling averages or sector-controlled measures, current CAPE readings remain at the high end of the post-1880 distribution.

Why don’t more investors use Shiller PE for tactical decisions?

The metric’s strength — its ten-year smoothing — is also its weakness for tactical use. CAPE moves slowly, providing little near-term signal. It can remain elevated or depressed for years before reversion occurs. This makes it useful for asset allocation and savings rate decisions but unsuitable for entry and exit timing within shorter horizons.

Last updated — 14 June 2026