Sources checked September 6, 2026. Unless stated otherwise, amounts, rates, and probabilities are illustrative assumptions. Institutional rules refer to Korea.
A pay rise arrives, but lunch and rent leave less money at the end of the month. Before reading another economic forecast, check whether you are comparing the same things. A bank balance measures currency; maintaining a life requires what that currency can buy.
Separate money amounts from purchasing power
Inflation describes a broad rise in prices. A price index combines purchases using expenditure weights, so a household whose spending differs from the average can experience a different change in living costs.1
Consider an invented example, not wage or inflation data. Monthly take-home pay rises from KRW 3 million to KRW 3.09 million, a 3% increase. If maintaining the same consumption costs 5% more, the new salary is worth 3.09 million ÷ 1.05 ≈ KRW 2,942,857 in last year's prices. Purchasing power falls about 1.90%. The exact change is 1.03 ÷ 1.05 - 1; subtracting the percentages gives an approximation.
Higher spending can also reflect different choices. Paying more for the same coffee differs from buying coffee more often. Separate price, quantity, and changes in your life when comparing budgets. Otherwise, an explanation about inflation can conceal a change you could actually make.
Explain individual prices with supply and demand
The basic market model relates what buyers want to purchase to what sellers offer. Other things equal, increased demand or reduced supply puts upward pressure on the equilibrium price.2 A hypothetical poor fruit harvest and a rise in local restaurant demand illustrate different starting points. Asking why one price changed differs from measuring economy-wide inflation. The model organizes questions; it is not a formula that precisely forecasts an actual price.
The cost of a choice extends beyond its price
Scarcity means resources cannot satisfy every possible use. Opportunity cost is the value of the best alternative you give up, rather than the sum of all rejected alternatives.3
Suppose a weekend course costs KRW 200,000. If rest was your best alternative use of that weekend, rest belongs in the comparison. Do not invent forgone wages from a job you would never have taken. The purpose is to understand what the choice displaces, not to assign a wage to every hour.
Also separate an unrecoverable course fee from the time you still have to spend. My suggested decision rule is to compare future learning with the best future use of that time. Money already lost cannot make an unhelpful next session useful.
Translate rates into everyday units
Interest is the price of borrowing or the return on lending money. A nominal interest rate records the agreed rate; a real rate accounts for inflation.4 With no taxes, a hypothetical 4% one-year deposit return and 3% inflation produce a real return of 1.04 ÷ 1.03 - 1 ≈ 0.97%.
An exchange rate tells you how much of one currency buys another.5 Ignoring conversion charges, a USD 100 purchase costs KRW 130,000 at KRW 1,300 per dollar and KRW 140,000 at KRW 1,400. The dollar price has not changed, but the expense in your budget has. These exchange rates are assumptions, not current quotes.
These relationships do not predict next month's currency or stock prices. First ask which part of your own finances a headline touches: loan payments, foreign purchases, or the purchasing power of savings.
A calculation to do today
Compare housing, food, and transport expenses in the same month of two years. Mark whether each change came from prices, quantities, or a life event such as moving. Subtract the extra cost of maintaining the same life from the increase in take-home pay. This is a personal budgeting record, not a replacement for an official price index.
The next chapter turns that record into a cash flow statement and a personal balance sheet.
Series contents · Next chapter: Building a system from your first paycheck
Footnotes
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European Central Bank, What is inflation?. Broad price changes, expenditure weights, and differences between household baskets. ↩
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Federal Reserve Bank of St. Louis, Market Equilibrium — The Economic Lowdown. Basic supply, demand, and equilibrium relationships; the fruit and restaurant examples are hypothetical. ↩
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Federal Reserve Bank of St. Louis, Scarcity — Explore Economics. Definitions of scarcity and opportunity cost. ↩
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European Central Bank, Nominal and real interest rates. The distinction between nominal and real rates; the numerical example is the author's calculation. ↩
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European Central Bank, What is the role of exchange rates?. Currency conversion concepts; the exchange rates used here are hypothetical. ↩
Sources
Related notes
This is a personal research note, not investment advice