The Price of Time
A rate is a price, and what it prices is time
Ask what an interest rate is and most explanations start with banks, or a central bank, or bond markets. None of those is the definition. An interest rate is a price — the price of time.
The trade is always the same shape. Someone holding money can spend it today. To hand it over instead, they must be compensated for the wait, because the future is uncertain and today's spending is real. That compensation is the rate. The borrower buys the right to spend now; the lender sells it.
This is why the same idea appears in a hundred costumes. A card rate, a car loan, a Treasury bill, a corporate bond, a deposit, the discount rate inside a pension model — each is a quote for one transaction: money now for money later, with a price attached to the delay. Read every one of them as time, priced in percent per year.
The unit professionals use is the basis point, one hundredth of a percentage point. A quote moving from 5.00% to 5.25% has moved 25 basis points. Small numbers, because the thing being priced is measured in years.
The policy rate is the shortest-dated money there is
Start at the shortest maturity that exists: one night. Banks hold balances at the central bank and lend them to each other for a single day. The policy rate is the price the central bank sets for that money. It is the shortest-dated price in the system.
It is not the price of your mortgage and it is not the price of a 30yr bond. It is the first domino. Every other rate in the economy is priced off the step above it, and the chain runs one way:
Money-market rates — Treasury bills, commercial paper, repo — sit just above the overnight rate, because they are short and close to riskless. The government curve sits above those: a 10yr bond ties money up for a decade, so its price must reflect the wait. Credit sits on top of the curve, because a company or a household pays the government yield for the same maturity, plus a spread for the chance of not being repaid.
Note the direction of causation. Each step is fed by the one before it, and the signal takes time to travel. A change at the top reaches a card rate in weeks and reaches a factory's investment decision over quarters. That lag is the whole reason policy is argued about in advance.
The yield curve is not a forecast
The yield curve is the set of government bond yields at different maturities, drawn on one chart. People read it as a forecast of the economy. That reading is too loose by half.
A long yield is made of exactly two pieces. One is the average short-term rate the market expects over the bond's life. The other is the term premium — the extra yield demanded for locking money up for years instead of rolling short bills. The expectations piece is the forecast. The premium is compensation for uncertainty, and it forecasts nothing.
Read our own snapshot from 2026-09-24. The 3-month bill yielded 4.24%. The 2yr yielded 4.81%, the 5yr 4.98%, the 7yr 5.10%, the 10yr 5.17%, the 20yr 5.53% and the 30yr 5.49%. The 2s10s gap — 10yr minus 2yr — was +0.36 points, or 36 basis points. The 3-month-to-10yr gap was +0.93 points, or 93 basis points.
Now decompose the long end. A 30yr yield of 5.49% is not a prediction that short rates average 5.49% for 30 years. It is the expected average short rate plus a term premium large enough to compensate 3 decades of unknown inflation and unknown policy. When someone says the curve is pricing something, that sum is what they mean.
Real vs nominal, and why the long end can detach
Every quoted rate is nominal, denominated in today's dollars. Subtract the inflation expected over the same period and you get the real interest rate — the return in actual purchasing power.
The arithmetic is checkable by hand. A nominal rate of 5.00% with expected inflation of 3.00% is a real rate of 2.00%. That is the number that decides whether saving is rewarded and whether borrowing to invest pays for itself.
This resolves a question that confuses people every week: how can a central bank cut its policy rate while the 30yr yield rises? Because the long end is not pricing this month's meeting. It is pricing the entire expected path of short rates plus the term premium, and both of those respond to inflation expectations and to how much long-dated risk investors will absorb. Cut today, and the long end can still climb if the cut reads as inflationary or if the premium widens.
Duration: why the long bond is where a rates view lives
Duration measures how much a bond's price moves when its yield changes, and it grows with maturity. A bond that repays you in 30 years has most of its value sitting in distant cash flows, so a change in the discount rate lands harder than it does on a bill maturing next quarter.
That is precisely why long bonds are the instrument where a rates view gets expressed. If you are right about the direction of yields, duration is the multiplier that turns a small move into a large return. If you are wrong, it is the multiplier that turns a small move into a large loss.
A single basis point is trivial on a 3-month bill and meaningful on a 30yr bond. Same information, same curve, different maturity — and a different size of outcome. Duration is the dial that sets how much of the curve's move you actually feel.
Related: Yield Curve · Term Premium · Real Interest Rate · Duration