Money Has a Time Value
A dollar today is worth more than a dollar in the future. This isn't just an opinion — it's a fundamental principle of finance called the time value of money.
Why? Several reasons: money received today can be invested and grow; inflation means future money buys less; and there's always some uncertainty about whether future money will actually arrive. All of these factors make present money more valuable than future money.
The time value of money underpins almost every financial concept: interest rates, loan repayments, investment returns, retirement planning, and the pricing of assets.
What Is an Interest Rate?
An interest rate is the cost of borrowing money — or the reward for lending it. It's expressed as a percentage of the amount borrowed or invested, typically per year.
If you deposit $1,000 in an account earning 5% annual interest, you'll have $1,050 at the end of the year. If you borrow $1,000 at 5% interest, you'll owe $1,050. The rate reflects the time value of money: the lender gives up the use of their money for a year and expects compensation.
Interest rates are set by a combination of central bank policy, inflation expectations, credit risk, and supply and demand for capital.
Compound Interest
Interest becomes powerful through compounding — earning interest on your interest. At 7% annual growth, $10,000 becomes roughly $20,000 in 10 years, $40,000 in 20 years, and $80,000 in 30 years. The growth accelerates because each year's interest becomes part of the principal for the next year.
Einstein allegedly called compound interest the eighth wonder of the world. Whether he said it or not, the point holds: time is the most important variable in compounding. Starting early matters far more than contributing large amounts late.
How Interest Rates Affect the Economy
Central banks use interest rates as the primary lever for managing economic activity. When they raise rates, borrowing becomes more expensive — people and businesses spend less, slowing the economy and reducing inflation. When they cut rates, borrowing becomes cheaper — spending and investment increase.
This is why interest rate decisions by central banks move financial markets. Higher rates make bonds more attractive relative to stocks; lower rates tend to push investors toward riskier assets in search of returns.
Practical Implications
The time value of money and interest rates show up directly in your financial life:
- Debt costs compound too. High-interest debt (like credit cards at 20%+) grows just as relentlessly as investments — only in the wrong direction.
- Discounting future income. A pension that pays out in 30 years is worth less today than the same amount received now. Understanding this helps evaluate financial offers.
- The cost of waiting. Every year you delay investing is a year of compounding you can never recover. The time value of money makes delay expensive.