U.S. investors are heading into one of the most important economic releases of the week with a familiar problem: the stock market is near record highs, but inflation remains a potential threat to the outlook.

The September Consumer Price Index, scheduled for release on Wednesday, October 14, will help investors judge whether price pressures are accelerating again or stabilizing after recent energy-cost increases.

According to forecasts cited in recent Reuters market coverage, economists expect headline CPI to rise approximately 3.7% year over year, while core inflation—which excludes food and energy—is expected to be around 2.5%.

Those figures are estimates, not confirmed results. The actual release could differ, and the market reaction will depend partly on how the numbers compare with expectations.

Inflation affects companies through several channels.

Higher prices for fuel, transportation, labor and raw materials can squeeze profit margins when businesses cannot pass the full increase on to customers. At the same time, persistent inflation can limit the Federal Reserve's ability to ease monetary policy.

That matters for stock valuations because investors often value companies partly on the profits they are expected to generate in the future. When interest rates rise, those future profits may become less valuable in today's terms.

This sensitivity is particularly relevant for expensive growth stocks, including parts of the technology sector.

A higher-than-anticipated CPI reading could revive concerns that inflation is proving more persistent than policymakers would like.

Investors might demand higher yields on Treasury securities or reduce expectations for future monetary easing. That could pressure high-valuation technology stocks, real estate investment trusts and other rate-sensitive investments.

Consumer-facing companies could also face pressure if higher living costs reduce households' discretionary spending.

A hot headline number would not automatically guarantee another Fed rate hike, however. Investors would still need to assess the details, underlying trend and policymakers' response.

A softer report could support a more constructive interpretation of the economic outlook.

If inflation moderates without evidence of a sharp deterioration in economic activity, bond yields could come under pressure and equity valuations might benefit.

Technology shares could respond positively because their valuations are particularly sensitive to changes in long-term discount rates.

However, a single encouraging report would not prove that inflation has been defeated. Investors would need confirmation from subsequent data.

This is a particularly important possibility.

Higher energy prices can push headline inflation upward even when underlying price pressures are less severe. If core inflation remains relatively contained, investors may conclude that at least part of the increase is being driven by energy rather than broad-based price acceleration.

That would still leave the economy exposed to further oil-price shocks, but it could produce a different monetary-policy interpretation from a simultaneous rise in both headline and core inflation.

Investors should not look only at the S&P 500's first reaction.

The two-year Treasury yield can provide clues about near-term expectations for Federal Reserve policy, while the 10-year yield influences borrowing costs and valuations across much of the economy.

Watch whether bond yields confirm the equity market's interpretation of the report. A stock rally accompanied by sharply rising yields may be less durable than one supported by easing inflation concerns.

Wednesday's CPI report will not determine the entire direction of the U.S. economy, but it could influence how investors price interest-rate risk over the coming weeks.

For now, three things matter most: the headline inflation rate, the core reading and the market's response through Treasury yields.

The biggest surprise may not necessarily be a high or low inflation number. It may be a reading that forces investors to reconsider assumptions they had already built into stock prices.