Interest rates are the percentage cost of borrowing money or the percentage reward for lending or saving it, usually stated per year. They apply to loans, mortgages, bonds and deposits, and they are the foundation of how cash flows are priced over time.
Think of an interest rate as the rental price of money. If you borrow, you pay it. If you save or hold a bond, you earn it. Rates are quoted by central banks as policy settings and by markets as yields on securities, and they feed through to almost every asset price.
What an interest rate actually measures
An interest rate compares money now with money later. It is calculated on a principal amount over a period. Lenders quote it as a percentage per year, then specify how it accrues. With simple interest, the charge is on the original principal only. With compounding, interest is added to the balance so future interest is earned or charged on earlier interest as well.
Two common styles of quoting can trip people up. A nominal annual rate without compounding tells you the yearly percentage but not how often interest is added. An effective annual rate reflects compounding during the year, so it is higher when interest is added monthly or daily. Cards, overdrafts and savings often use compounding, while some loans highlight a headline rate then state the compounding rule in the small print.
In markets, yields on bonds are the interest rate that equates the current price to the present value of all coupons and principal. That calculation is the same time value logic you see in a loan agreement, just applied to traded securities.
Policy rates, market rates and the yield curve
Central banks set short term policy rates to steer the economy. The exact framework varies by country, but it typically centres on an overnight rate for bank reserves and a target range. Policy decisions and guidance shape the rates that banks quote to each other, then filter into loan and deposit rates for households and businesses. Bodies like the Federal Reserve or the ECB also use tools such as asset purchases or sales to influence broader financial conditions.
Beyond the overnight horizon, markets set rates by supply and demand for government bills and bonds. Plot those yields by maturity and you have the yield curve. A curve that rises with maturity usually signals that investors want more return to lock money away for longer, often reflecting expectations for higher inflation or term risk. A flatter or inverted curve can indicate expectations that policy rates will fall later, though interpretations depend on context.
Corporate borrowing costs start with the government yield curve as a base, then add a credit spread for the issuer’s risk. Mortgage rates and other consumer loans often reference a market benchmark plus a margin for credit and operating costs.
Nominal and real rates, and why the difference matters
Most quoted rates are nominal, which means they are not adjusted for price changes in the wider economy. Real rates subtract inflation to show the change in purchasing power. If your savings account pays 3 percent but prices rise 4 percent, your real return is roughly minus 1 percent. That calculation is approximate unless you use exact formulas, but it gives the right intuition.
Real rates matter for investment decisions because they describe the true reward for delaying consumption. When real rates are high, borrowing to spend is more expensive in purchasing power terms and saving is more attractive. When real rates are low or negative, borrowers are effectively helped by rising prices, and investors often look further out the risk spectrum for returns.
Markets track real yields using inflation linked bonds and by inferring expectations from nominal yields minus measures of expected inflation. The gap between the two can shift quickly when investors change their view of future price trends or central bank credibility.
Fixed or variable: how rates show up in loans and savings
Loans and deposits can be fixed rate or variable rate. A fixed rate stays the same for a set period, which makes budgeting simple but means you do not benefit if market rates fall. A variable rate moves with a benchmark, for example a recognised overnight index or a lender’s reference rate, plus a margin. Variable loans pass through market changes more quickly, which can be helpful when rates fall and painful when they rise.
Credit cards and overdrafts usually compound interest daily or monthly, then bill you monthly. Missing a payment can increase the effective rate sharply due to fees that also compound. Savings products can be the mirror image, paying interest monthly or annually and sometimes offering a higher rate if you lock your money away for longer.
On the investment side, a bond with a fixed coupon pays a set amount each period until maturity. A floating rate note resets its coupon periodically based on a benchmark, which reduces price sensitivity to changes in short term rates but passes rate risk to the income stream instead.
Why interest rates move asset prices
Rates set the discount rate that converts future cash flows into a price today. Raise the discount rate and the present value falls, all else equal. That is why bond prices drop when yields rise. For example, if a £1,000 bond pays £50 a year, a market yield of 5 percent suggests a price near £1,000. If similar bonds suddenly yield 6 percent, investors demand a lower price so that the £50 coupon equates to a 6 percent return.
Equities are affected through the same cash flow logic and through competition for capital. Higher risk free rates lift required returns for shares, which can compress price to earnings multiples, especially for companies whose expected profits are far in the future. Property values and infrastructure assets react in similar ways because their valuations depend on discounted cash flows.
Currencies also respond. Higher relative short term rates can attract capital, supporting the exchange rate, while expectations for future cuts can do the opposite. The exact move depends on many factors, including growth prospects and perceived risk, but rates are a central part of the story.
How traders and investors watch and trade rates
Professionals track policy announcements, speeches, and data that shape rate expectations. Central banks signal their bias using statements and projections. Market pricing in futures, swaps and government bonds converts those expectations into a curve that updates in real time. For a high level primer on the price of money itself, see our page on interest.
There are several ways to trade interest rate views. Short dated rate futures reflect expected policy settings over set quarters. Government bond futures and cash bonds allow positioning along the curve. Interest rate swaps exchange fixed payments for floating ones, which can hedge a borrower’s exposure or express a macro view. Options on rates and bonds give convex exposure, useful when you care about volatility or tail risks. Exact contract terms and symbols vary by venue and provider.
Portfolio managers also manage rate sensitivity inside other assets. Equity investors look at sector tilts that react differently to rising or falling yields. Credit investors separate moves due to underlying rates from changes in credit spreads. Even crypto markets watch rates because they influence dollar liquidity and the opportunity cost of holding risk assets.
Across all of this, remember that rate mechanics differ by jurisdiction and can change over time. What does not change is the core idea. Interest rates price money through time, and that price touches almost every decision in finance.