What Interest Is
Interest is the price of using someone else’s money for a period of time.
If Alice has $10,000 she does not need right now, and Bob needs $10,000 to start a business, Alice invests in Bob’s business, she is giving up what she could have bought today so Bob can use it instead. Interest is the compensation Alice gets for that sacrifice, and what Bob pays for using money before he has earned it.
That is all interest is: a price. The price of time.
What Determines the Rate
Three factors determine how high an interest rate is:
-
Time preference - most people prefer things now rather than later. To get you to save instead of spend, the borrower must offer you something extra. That extra is interest.
-
Risk - there is always a chance the borrower will not pay you back. Higher risk means higher interest to compensate. This is why credit cards charge more than government bonds.
-
Inflation - if prices are rising at 3%, a lender who charges 0% is losing 3% per year. Interest rates must be above inflation for lending to make sense. The difference between the interest rate and inflation is the real interest rate - the actual reward for waiting.
What Interest Rates Do
Interest rates are signals that coordinate the entire economy’s decisions about the future.
Low rates make borrowing cheap. Businesses borrow to build factories and hire workers. People borrow to buy houses. Low rates encourage investment in the future.
High rates make borrowing expensive. Only the most promising projects make sense. People save more because they get a better return. High rates cool an overheated economy and encourage patience.
Central banks set short-term rates to steer the economy - lowering them to encourage growth, raising them to fight inflation. But long-term rates are set by millions of lenders and borrowers acting on their own judgment. If investors expect inflation, long-term rates will rise no matter what the central bank does.
Why It Matters
Low rates are not “free money.” They encourage borrowing, which is fine, but they also punish savers - retired people who saved their whole lives suddenly earn nothing on their bank accounts. Low rates also inflate asset prices (houses, stocks), making inequality worse: those who already own assets get richer, while those who do not find it harder to buy in.
When rates are kept artificially low for too long, people take on debt they cannot repay when rates eventually rise. That is how financial crises happen.
Common Misunderstandings
Low rates are not always good. They help borrowers and hurt savers. The same rate that makes your mortgage affordable also shrinks your grandmother’s savings.
The central bank does not control all rates. It sets the short-term policy rate. Long-term rates are determined by the market’s view of the future - inflation expectations, growth prospects, global capital flows.
See also: Money & Currency, Prices, Macroeconomics