What Actually Moves Major Stock Indices

Everything so far has covered a general concept. This lesson applies it to the major US indices — what determines each one's direction, and why they don't always move together even though they're often talked about as if they do.

S&P 500

What it is: 500 of the largest US companies, weighted by market cap — the broadest commonly-traded gauge of the market.
Key data: Fed policy, Treasury yields, aggregate earnings, GDP and employment.
Sector mix: Diversified across tech, financials, healthcare, industrials, energy — no single sector dominates it the way tech dominates the Nasdaq.
Typical behaviour: Reacts to broad news more evenly across sectors, since no single industry can move it alone.

Nasdaq 100

What it is: The 100 largest non-financial Nasdaq companies, heavily concentrated in tech and a handful of mega-caps.
Key data: Same macro inputs as the S&P 500, but outsized sensitivity to interest-rate expectations and mega-cap earnings.
Sector mix: Dominated by a handful of very large growth companies — its direction can hinge disproportionately on a few names' earnings.
Typical behaviour: More volatile than the S&P 500 in both directions, and more reactive to rate news specifically.

Dow Jones Industrial Average

What it is: 30 large, established companies, price-weighted rather than market-cap weighted — higher-priced stocks influence it more, regardless of company size.
Key data: Broad economic data, weighted more toward industrials, financials and consumer staples than tech.
Typical behaviour: Somewhat less volatile than the Nasdaq, given lower concentration in rate-sensitive growth names.

Russell 2000

What it is: 2,000 small-cap US companies — the standard gauge for smaller, domestically-focused businesses.
Key data: US-specific growth and credit conditions matter more here, since small caps lean more on domestic revenue and bank lending.
Typical behaviour: Especially sensitive to rates and credit conditions — small companies carry proportionally more debt and refinance more often, so borrowing-cost changes hit harder.

Why interest rates hit the Nasdaq hardest

The single most important mechanism for understanding why these indices don't move in lockstep.

A stock's price reflects future earnings discounted back to today's value — the higher the rate used, the less those earnings are worth today. Growth and tech companies are valued on earnings expected years out, so their valuations are far more sensitive to that discount rate than a mature, steady-earnings industrial company.

Key takeaway

🎯 Rising rates pressure growth-stock valuations more than value-stock valuations, because more of a growth company's worth sits further out in time — exactly why the Nasdaq reacts more sharply to rate surprises than the Dow.

Example

📊 A hawkish Fed surprise can send the Nasdaq down sharply while the Dow only falls modestly the same day — not because Dow companies are unaffected by higher rates, but because Nasdaq earnings are weighted much further into the future, making valuations far more rate-sensitive.

Earnings season and mega-cap concentration

Because the Nasdaq 100 is so concentrated, it can be moved disproportionately by just a handful of names' earnings during earnings season — far less pronounced in the broader S&P 500 or small-cap-heavy Russell 2000.

Why it matters

ℹ️ When trading Nasdaq futures, it's worth knowing whether a major constituent reports earnings that week — a single mega-cap miss or beat can move the whole index even with no macro news at all.

Sector rotation

Money moving between sectors — into tech and out of energy, or vice versa — can cause indices to diverge even on a quiet data day. Often driven by relative-value shifts or changing rate expectations rather than any single headline.

Common mistake

🚫 Don't assume every index move needs a fresh news catalyst. A quiet macro day can still see indices diverge purely from sector rotation — check sector-level performance before concluding "nothing is happening."

Putting it together

Every index here is shaped by the same forces — Fed policy, rates, yields, risk sentiment. What differs is sensitivity: how concentrated each one is in rate-sensitive growth names versus steadier, diversified or small-cap businesses. That's the main reason the S&P 500, Nasdaq 100, Dow and Russell 2000 can tell very different stories on the same day.