Inflation: Why a Dollar Today Isn't a Dollar Tomorrow

What Inflation Is

Inflation is a sustained increase in the general price level of goods and services across an economy over time. It's typically measured as a percentage change over a year: if inflation is running at 3% annually, a basket of goods that cost $100 a year ago now costs roughly $103.

Inflation isn't about any single item getting more expensive; plenty of individual prices rise and fall for their own reasons, like a bad harvest or a new competitor, without that counting as inflation. Inflation specifically describes a broad, sustained rise across the economy as a whole, usually tracked through indexes like the Consumer Price Index, which follows the cost of a representative basket of goods and services.

Purchasing Power: The Real Cost of Inflation

The practical effect of inflation is that the same amount of money buys less over time, a decline known as purchasing power. If you keep $1,000 in cash under a mattress for a year while inflation runs at 3%, that $1,000 still says $1,000 on it, but it can only buy what roughly $970 could have bought a year earlier.

This is why savers care about the difference between a nominal return, the stated interest rate, and a real return, the return after subtracting inflation. A savings account paying 2% interest during a year of 3% inflation is actually losing purchasing power, even though the account balance is technically growing.

What Causes Inflation

Inflation is often explained through two broad lenses. Demand-pull inflation happens when overall demand for goods and services grows faster than the economy's ability to produce them, so more dollars chase a relatively similar amount of goods, bidding up prices. Cost-push inflation happens when the cost of producing goods rises, for example a spike in energy or raw material prices, and businesses pass those higher costs on to consumers.

In practice, real-world inflation is usually driven by some combination of these forces rather than a single clean cause, which is part of why it can be difficult to predict or control precisely.

A Worked Example

Suppose your favorite coffee costs $4 today, and inflation runs at a steady 3% per year. Using the same compounding logic as investment growth, that coffee would cost roughly $4 × (1.03)^10 ≈ $5.38 in ten years, not because the coffee changed, but because the same nominal price buys less over time across the whole economy, and businesses adjust their prices to keep up with rising costs.

This is also why a fixed retirement income that never adjusts for inflation loses real value every year it stays flat, even if the dollar amount on the check never changes.

Why Some Inflation Is Considered Normal

Most central banks, including the U.S. Federal Reserve, aim for a low, steady rate of inflation, commonly cited around 2% per year, rather than zero. A small, predictable amount of inflation is generally viewed as consistent with a healthy, growing economy, while deflation, or falling prices, can discourage spending, since people may delay purchases expecting even lower prices later. The goal isn't to eliminate inflation entirely, but to keep it low and predictable enough that businesses and households can plan around it.