What Drives Index Prices

Stock markets are forward-looking. By the time a recession shows up in the GDP data, stock markets have usually already been falling for months. They priced in the recession before it arrived. By the time an economic recovery shows up in employment data, stock markets have usually already been rising. They priced in the recovery before the data confirmed it.

This is why understanding what drives index prices requires understanding not just current economic conditions but the expectations and narratives that investors are currently pricing in. When you trade an index, you are not trading the economy as it is. You are trading the economy as investors believe it will be.

Think about why you would buy a share of any company. You are buying a claim on that company''s future earnings. If the company earns more profit in the future than it does today, your share is worth more. If it earns less, your share is worth less. Scale that up to 500 companies and you have the S&P 500.

This is why earnings season, the four to six week period each quarter when most major companies report their financial results, is the most important fundamental event for equity indices. When the majority of large companies beat their earnings expectations and raise their guidance for the next quarter, the index tends to rise. When results are weak and companies cut their outlooks, the index tends to fall.

The quarterly earnings season is not just about individual companies. The collective results tell you whether the US economy, or the UK, or Germany, or Japan, is performing better or worse than expected. When S&P 500 companies collectively beat earnings estimates by a large margin, it is telling you the American economy is stronger than analysts thought.

The relationship works through two channels.

The first is the discount rate. Every stock is theoretically valued by taking all its expected future earnings and discounting them back to their present value. When interest rates rise, future earnings are worth less in today''s terms and valuations fall. When rates fall, future earnings are worth more and valuations rise.

The second is competition from bonds. When interest rates are very low, bonds and cash deposits pay almost nothing. Investors seeking returns have little choice but to put money into equities. When rates rise significantly, bonds and cash deposits start paying attractive returns again. Some money rotates out of stocks and into bonds, pushing equity prices lower.

This is why the Federal Reserve''s interest rate decisions are not just a forex story. They are one of the most important drivers of US and global equity markets simultaneously.

Strong employment data, a better than expected NFP reading, tells the market that the economy is healthy, consumers have jobs and income, and corporate revenues are likely to hold up. Indices tend to rise on this news, though with a nuance: if employment is so strong that it might push inflation higher and force the Fed to keep rates elevated, the stock market may actually fall on very strong employment data.

GDP growth readings tell the market whether the economy is expanding or contracting. Strong GDP growth tends to support equity markets. GDP contraction, particularly two consecutive quarters of it, signals a recession, which is reliably negative for equity prices.

Inflation data has become one of the most market-moving releases for equity indices. When inflation is higher than expected, the market immediately begins pricing in a higher probability of rate hikes or fewer rate cuts, both of which are negative for equity valuations. When inflation falls faster than expected, the market begins pricing in rate cuts, which are positive for equities.

The VIX, the Volatility Index, sometimes called the fear gauge, measures implied volatility in S&P 500 options. It gives a real-time reading of how anxious or complacent the market is. When the VIX is low and falling, investors are calm. They are buying equities confidently and not spending much to insure against downside. When the VIX spikes sharply, fear has entered the market. Investors are buying protection aggressively, which tells you something significant has shifted.

The COVID crash in March 2020 saw the VIX spike to its highest level ever recorded, above 80, a record that as of 2026 still stands, as the fastest bear market in history unfolded. The 2022 bear market saw the VIX stay elevated throughout the year as the Fed''s aggressive rate hikes created persistent uncertainty.

Experienced equity traders always know where the VIX is. A low VIX does not mean nothing bad can happen. It means investors are not currently paying to protect against bad things happening. That complacency itself can be a warning sign.