The S&P 500 Is Down 9% and Logging Its Worst Week in Four Years. Here Is What the Iran War Is Doing to Your Investments — and What to Actually Do.

On March 28, 2026, the New York Times ran a headline that captured the mood exactly: 'Stocks Keep Falling as Investors Lose Patience With the War in Iran.' The S&P 500 is down nearly 9% from its January high. The weekly losing streak is the worst in roughly four years — since the 2022 inflation shock that followed Russia's invasion of Ukraine. Oil is at $140 per barrel. Gas is at $9 in California. And millions of Americans who check their 401(k) balances this weekend are going to see numbers that trigger panic. Before you do anything with your investments, read this first.

What Is Actually Driving the Market Decline

The current market decline has three interconnected causes that are important to distinguish, because they have different implications for how long the downturn lasts and how severe it gets.

• Oil price shock from Hormuz uncertainty: when the Strait of Hormuz — through which 20% of global oil supply travels — faces disruption risk, oil prices rise. Rising oil prices are inflationary. Inflation expectations cause the Federal Reserve to hold interest rates higher for longer. Higher interest rates reduce the present value of future corporate earnings — which mathematically reduces stock prices. This is the transmission mechanism from war to market decline.
• Corporate earnings guidance cuts: companies that depend on global supply chains, energy inputs, or consumer discretionary spending are cutting their forward earnings guidance. Airlines, retailers, manufacturers, and tech companies with data centers all face higher energy costs. Lower expected earnings directly reduce fair value estimates.
• Sentiment and risk premium: beyond the direct economic effects, markets are pricing in uncertainty. When the outcome of a geopolitical conflict is genuinely unknown, investors demand a higher risk premium — a discount on risky assets that reflects their uncertainty. This sentiment effect often moves faster than the underlying economics.

Which Investments Are Going Up and Which Are Going Down

• Going down: technology stocks (higher energy costs for data centers, AI infrastructure), consumer discretionary (retail, restaurants, travel — consumers spending on gas instead), airlines (fuel cost spike), homebuilders (higher mortgage rates from Fed rate pressure).
• Going up: energy stocks (Constellation Energy, Vistra, Exxon, Chevron — direct beneficiaries of high oil prices), defense contractors (Raytheon, Northrop Grumman, Lockheed Martin — war spending), gold and Treasury bonds (safe haven assets), nuclear energy stocks (long-term beneficiary of AI power demand thesis).
• Mixed: banks and financials (benefit from higher interest rates, hurt by loan default risk if recession occurs), healthcare (generally defensive, less correlated to geopolitical events), consumer staples (food, household products — relatively stable).

Historical Context: What Happens to Markets During Wars

The instinct to sell everything when a war starts is understandable — but the historical data argues strongly against it. Yale economist Robert Shiller's analysis of market reactions to geopolitical events finds that markets tend to fully recover within 12–18 months of the initial shock in conflicts that do not directly destroy US economic infrastructure. The Gulf War (1990–91), Kosovo (1999), Afghanistan (2001), Iraq (2003), and Russia-Ukraine (2022) all produced short-term market declines followed by recovery. The key question is always: does this conflict permanently impair US economic capacity? The Iran War, as currently constituted, does not appear to meet that threshold.

What AI Models Are Saying About the Market Right Now

An interesting meta-development in 2026's market volatility: AI financial analysis tools are being used at unprecedented scale by retail investors trying to make sense of the situation. JPMorgan's AI market analysis, Bloomberg's AI financial assistant, and general-purpose models like Claude and ChatGPT are all fielding enormous volumes of 'what should I do with my portfolio?' queries. The answer these systems generally provide is consistent with what human financial advisors say — and it is worth hearing.

• Do not make portfolio changes based on short-term news events: market timing around geopolitical events has historically reduced long-term returns for retail investors who attempt it. The costs of being wrong about timing (missing the recovery) exceed the benefits of being right (avoiding the initial decline) in most historical cases.
• Review your actual risk tolerance, not your theoretical one: a 9% market decline is a good test of whether your asset allocation actually matches your psychology. If you are losing sleep over it, your portfolio may be more aggressive than you genuinely can tolerate. That is valuable information — but the time to act on it is after markets stabilize, not during a panic.
• Check your rebalancing: if the decline has significantly shifted your asset allocation away from your target, a mechanical rebalance — buying the now-cheaper equities with bond or cash proceeds — is a historically effective approach that does not require any prediction about market direction.
• Evaluate your timeline: if you need the money in under 3 years, it should not be in equities regardless of the current situation. If your timeline is 10+ years, short-term declines are historically irrelevant to your outcome.