Why do GDP figures have such a significant impact on the stock market?

When we look at economic news, we often hear the term GDP so frequently that it almost becomes familiar. Many people know that GDP relates to a country's economy, but if asked what GDP actually is and why its changes cause the SET Index to fluctuate, the explanation might not be very clear.

Recently, I studied this topic seriously because I wanted to understand why GDP figures are so important to investment markets as we see today. So, I’d like to share my understanding with everyone.

Simply put, what is GDP? It is the total value of all goods and services produced by a country within a certain period. It includes everything that occurs within the country's borders, whether produced by Thai people or foreign companies based here. This figure is calculated annually, sometimes quarterly, to give a clearer picture of the economy's direction.

The calculation formula is quite straightforward: GDP = C + G + I + NX, where C is consumer spending, G is government expenditure, I is private and public investment, and NX is net exports (exports minus imports).

Consumer spending makes up the majority of GDP. If Thai people are willing to spend money on goods, GDP will increase. But if people are fearful and cut back, GDP will decrease. Business investment is also important because when companies buy machinery, build factories, or expand their operations, it indicates economic strength.

Now, the key question is: why does GDP matter, and how does it relate to the stock market? Listed companies generate revenue within the country. If GDP is high, it means the economy is doing well, and companies have more profit opportunities. Stock prices tend to rise. Conversely, if GDP is low, it indicates a weak economy, companies may earn less, and stock prices tend to fall.

There are two types of GDP to know: Nominal GDP and Real GDP. Nominal GDP is the figure that hasn't been adjusted for inflation. If prices rise, Nominal GDP also increases, even if the actual quantity of goods produced hasn't changed. Real GDP adjusts for inflation, providing a true measure of economic growth by reflecting the real increase in production.

When looking at GDP figures for the economy, it can be difficult to tell whether the increase is due to actual growth in production or just higher prices. That’s why economists use Real GDP, which is adjusted to a base year, allowing for genuine comparisons across different years.

For those analyzing the stock market, understanding what GDP is and how it affects the economy helps us make better investment decisions. When new GDP figures are announced, investors react immediately—stock prices may go up or down depending on whether the figures are better or worse than expected.

However, it’s important to remember that GDP is just one indicator. It doesn’t tell the full story of the economy. Other data, such as unemployment rates, inflation, and foreign capital inflows, should also be considered. Combining all these factors provides a clearer picture of the economic and market outlook.