How Stock Markets Work and What Drives Daily Price Swings
Published:
In brief
Stock markets work by matching buy and sell orders for shares of listed companies; a price rises when buy demand outweighs sell supply and falls when the reverse happens. Day-to-day swings are driven mainly by corporate earnings, interest-rate expectations, inflation and economic data, geopolitical events, and investor sentiment — a mix on display in trading on October 12, 2026, when oil prices and upcoming bank earnings moved major US indexes.
How a stock exchange sets a price
A stock market is a venue where investors buy and sell ownership shares in publicly listed companies. Prices are not fixed by any single party; they emerge continuously from the matching of buy orders and sell orders. When more investors want to buy a stock than sell it, the price moves up; when sellers outnumber buyers, it moves down, according to an explainer published by trading-education site CapMint.
Because buying and selling never stop during trading hours, prices can shift from one trade to the next. The US Securities and Exchange Commission's investor-education materials remind investors that "all investments involve some degree of risk" and that the value of shares can fall as well as rise.
What moves prices day to day
CapMint's breakdown of market drivers groups the forces behind daily price changes into several categories that recur in financial news coverage.
Corporate earnings and actions: quarterly results, dividend announcements, stock splits and mergers shift how investors value a company.
Interest rates and monetary policy: central bank decisions on rates change how attractive stocks are compared with bonds and savings.
Macroeconomic data: inflation, GDP growth, unemployment and consumer-confidence reports reshape expectations for corporate profits.
Geopolitical events: wars, sanctions and supply disruptions can move commodity prices and broader market sentiment.
Investor sentiment: CapMint's analysis notes that positive developments, such as strong earnings or favourable economic indicators, tend to boost investor confidence and push prices higher, while crowd-following behaviour — sometimes called herd mentality — can amplify declines once sentiment turns negative.
This week's trading illustrates the pattern
US index levels at Monday's close (October 12, 2026) showed the three major benchmarks moving in different directions on the same day, a sign that different sectors were reacting to different news, according to market data reported by Reuters via Investing.com.
US stock indexes, close of October 12, 2026
Index
Close
Change
S&P 500
7,807.24
-0.06%
Dow Jones Industrial Average
51,850.55
+0.38%
Nasdaq Composite
27,245.90
-0.44%
Oil was a key factor behind the moves. Reuters reported via Investing.com that crude prices surged after deadly strikes on Riyadh's international airport over the weekend, overshadowing potential supply increases from Russian diesel exports. Separately, 247wallst.com reported Brent crude trading near $106 a barrel, attributing the rise to disruption from the conflict involving Iran; the two outlets pointed to different elements of the same regional tension as the trigger.
Earnings season added another driver. Reuters, via Investing.com, reported that Goldman Sachs, Citigroup and JPMorgan Chase were due to report results on Tuesday, October 13, with S&P 500 earnings for the quarter projected to rise 30.6% according to LSEG IBES data. Interest-rate expectations also weighed on sentiment: Cleveland Federal Reserve President Beth Hammack said the central bank should move "relatively quickly" toward restrictive policy, and traders were pricing a 22% probability of a rate move this month, Reuters reported.
You're walking down a train line and you don't know...if a train is coming.
— Robert Pavlik, senior portfolio manager at Dakota Wealth, quoted by Reuters via Investing.com
Why this matters when the economy looks uncertain
None of these drivers act alone. A single day's move in an index is usually the net result of earnings news, bond-yield shifts, commodity prices and shifting sentiment arriving at the same time, which is why financial coverage of any given trading session tends to cite several factors rather than one single cause.
Questions
What actually sets a stock's price?
A stock's price is set by the continuous matching of buy and sell orders on an exchange; when buy demand exceeds sell supply the price rises, and it falls when supply exceeds demand, according to CapMint's market-factors explainer.
Why do stock markets move even without major news?
Daily moves reflect many simultaneous factors — earnings updates, interest-rate expectations, economic data and investor sentiment — so some price movement happens even on days without a single headline event, per the CapMint breakdown of market drivers.
How do interest rates affect stock prices?
Higher or more restrictive central bank policy changes how attractive stocks are relative to bonds and savings; in October 2026, Cleveland Fed President Beth Hammack said policy should move "relatively quickly" toward restrictive territory, a comment Reuters reported was weighed by markets alongside rate-hike probability pricing.
Why did oil prices affect stock indexes this week?
Reuters (via Investing.com) linked the oil-price rise to strikes on Riyadh's international airport, while 247wallst.com attributed Brent crude's rise near $106 a barrel to the conflict involving Iran; both reports tied crude's move to the same regional tensions, which also affected broader market sentiment.
Why does earnings season move the whole market?
When major companies — including large banks such as Goldman Sachs, Citigroup and JPMorgan Chase — report results, investors use that data to judge the health of the broader economy; Reuters reported S&P 500 earnings for the quarter were projected to rise 30.6% according to LSEG IBES data.
This piece was prepared with artificial intelligence and passed an automated source check before publication. If you see an error, ask for a correction. Request a correction or reply · How we make this
China and the United States are each expanding their economic footprint in Europe through different tools: Chinese manufacturers are winning market share in cars, batteries and machinery, while the US has used tariff threats to reshape trade terms with the EU. Eurostat and EU industry data for 2025 show both trends accelerating at once, raising questions for European policymakers and businesses.
Common Table Group, led by coffee entrepreneur Thomas Anderson, has agreed to buy 57 former Beefeater, Brewers Fayre and Cookhouse restaurant sites plus one Premier Inn hotel from Whitbread, with reopenings planned from mid-November 2026. The deal is one of two separate agreements reviving part of the restaurant estate Whitbread shut down after closing its branded chains in September 2026.
Robert E. Hall of Stanford University and Michael Woodford of Columbia University won the 2026 Nobel Prize in Economic Sciences, announced October 12, for work on the microeconomic foundations of macroeconomic stabilization. The Royal Swedish Academy of Sciences said their models explain how household and business decisions shape inflation and unemployment. The two share the 12 million Swedish kronor (about $1.2 million) prize.
South Korea's KOSPI index closed at 6,384.24 on October 12, 2026, down 3.65% and its lowest level in more than two months, as foreign investors extended a fifth straight day of net selling. The drop caps a year in which foreign investors pulled $131 billion out of Korean equities, the largest outflow among major Asian markets, as enthusiasm for AI-linked chipmakers cools.
