S&P 500 at a P/E of 41.87: what returns to expect over 10 years

S&P 500 at a P/E of 41.87: weak returns or double digits?

With a P/E of 41.87, the S&P 500 is trading at levels that have historically preceded weak ten-year returns. Yet a Monte Carlo simulation using market data suggests an annual average of 14%. The gap between these two views could hardly be wider.

The P/E ratio is not what it seems

An index's P/E changes every quarter as corporate earnings come in. That 41.87 could fall to 30 if companies beat expectations, or rise to 80 if they disappoint. The valuation ratio is therefore a snapshot, not a movie. That said, when the snapshot shows levels this high, common sense suggests tempering expectations.

The Monte Carlo sees no end of the world

The Monte Carlo simulation, a standard tool in quantitative finance, yields an annual average of 14.01% over five years, with a median of 13.29%. Even in the worst scenario (10th percentile), returns would be positive: 2.10% a year. The probability of a loss over the period is just 5.7%. The data applied to the MSCI World, using a Vasicek model, point in the same direction, although the analysis breaks off without a conclusion.

The elephant: artificial intelligence

There is an elephant in the room: AI. Whether the P/E normalizes or shoots up depends on Nvidia's earnings and on the market continuing to fund AI. If that sector loses access to credit, money will flee into fixed income and into whatever sector bubbles next.

Two methods, two answers. The P/E warns of a mediocre future; the Monte Carlo promises double digits. Reality, as almost always, will lie somewhere in between. But given the valuation, it is wise not to bet everything on a single tool.