Understanding Interest Rates Revision Notes | GCSE AQA Economics

1. Why Interest Rates Matter

Every time someone takes out a mortgage, a student loan, or a credit card, interest rates determine how much that borrowing actually costs. And every time someone puts money in a savings account, interest rates determine what they earn. These rates touch almost every corner of the economy.

For AQA GCSE Economics Paper 2, interest rates sit within the macroeconomic topic of how the economy works. You need to know what an interest rate is, and — crucially — why different loans carry different rates. Both of those ideas appear directly in exam questions.

2. What Is an Interest Rate?

Think of borrowing money like renting a flat. When you rent, you pay the landlord for using their property. When you borrow money, you pay the lender for using their funds — and that payment is called interest. The interest rate is the price of that borrowing, expressed as a percentage of the original sum.

Here is a concrete example. Priya borrows £1,000 from a bank at an annual interest rate of 5%. After one year, she owes the original £1,000 plus £50 in interest — a total of £1,050. That £50 is the price she pays for using the bank's money. From the bank's perspective, that £50 is the reward for lending.

Interest rates work in both directions. When Mohammed deposits £500 into a savings account at 3% per year, the bank pays him £15 after twelve months. The rate is now his reward for letting the bank use his money. This dual role — cost for borrowers, reward for savers — is central to how interest rates influence economic behaviour.

Worked example: Calculating Simple Interest on a Loan

Ben borrows £2,000 at an annual interest rate of 4%. Calculate the total amount he repays after one year.

1. Principal = £2,000; Annual interest rate = 4% — The principal is the original amount borrowed. The rate tells us what percentage of that is charged each year.
2. Interest = £2,000 × (4 ÷ 100) = £2,000 × 0.04 = £80 — Convert the percentage to a decimal first: 4 ÷ 100 = 0.04. Then multiply by the principal.
3. Total repayment = £2,000 + £80 = £2,080 — Ben repays the original loan plus the interest. The interest is the cost of borrowing.
4. £80 ÷ £2,000 = 0.04 = 4% ✓ — Divide the interest by the principal and convert back to a percentage to confirm the rate is correct.

Answer: Ben repays £2,080 in total. The interest cost is £80.

Now that the definition is pinned down, a key question follows: if interest rates are set as percentages, why do different loans carry different rates? A mortgage might charge 5%, while a payday loan charges 1,000% or more. That gap is not random — it reflects a set of identifiable economic factors.

3. Factors That Influence Different Rates of Interest

The interest rate on any particular loan is shaped by several overlapping factors. The Bank of England's base rate provides the foundation, but lenders then adjust upwards based on the specific characteristics of each borrowing situation. Understanding these factors lets you explain — not just describe — why rates differ.

When the base rate rises, commercial banks face higher costs for borrowing from the Bank of England. They pass those costs on by raising the rates they charge customers. When the base rate falls, borrowing becomes cheaper across the economy. This is the primary lever of monetary policy.

• The Bank of England base rate: sets the floor for all other rates in the economy
• Risk of default: lenders charge more when there is a greater chance the borrower will not repay
• Duration of the loan: longer-term loans typically carry higher rates because the lender's money is tied up for longer and uncertainty increases over time
• Amount borrowed: very large loans may attract lower rates due to economies of scale in lending; very small loans may attract higher rates because fixed administrative costs are spread over a smaller sum
• Competition between lenders: more competition in the lending market tends to push rates down as banks compete for customers
• Inflation expectations: if lenders expect inflation to rise, they demand higher rates to ensure the real value of repayments is not eroded

The most important of these for exam purposes is risk. Lenders cannot be certain every borrower will repay. To compensate for that uncertainty, they add a risk premium on top of the base rate. The higher the perceived risk, the larger the premium — and the higher the interest rate charged.

Consider two borrowers: Aisha has a strong credit history, a stable income, and is buying a house as security against her mortgage. Chloe has missed loan repayments before and wants an unsecured personal loan. Aisha's lender faces low risk and charges 4%. Chloe's lender faces high risk and charges 18%. The difference is almost entirely explained by the risk premium.

Duration matters too. When a bank lends money for 25 years on a mortgage, it cannot be certain what will happen to inflation, the economy, or the borrower's circumstances over that period. That uncertainty is a form of risk — and lenders price it in. This is why fixed-rate mortgages over longer terms tend to carry higher rates than shorter-term deals.

Inflation expectations add another layer. If a lender expects prices to rise by 3% per year, a loan at 2% interest would actually lose the lender real purchasing power — they would get back less in real terms than they lent. To protect against this, lenders build expected inflation into the rate they charge. This connection between inflation and interest rates is a recurring theme in macroeconomics.

4. How Interest Rates Affect the Economy

Earlier we established that interest rates are the price of borrowing. Now we can build the chain of analysis that examiners reward: how does a change in interest rates ripple through the wider economy?

When the Bank of England raises the base rate, borrowing becomes more expensive across the economy. Consumers with mortgages face higher monthly repayments, leaving less disposable income for other spending. Businesses find it costlier to borrow for investment. Both effects reduce aggregate demand (AD) — the total spending in the economy — which can slow growth and reduce inflationary pressure.

The reverse chain applies when rates fall. Lower borrowing costs encourage consumers to take out loans and spend more. Businesses invest more readily. AD rises, output increases, and employment tends to grow. This is why the Bank of England cuts rates during economic downturns — it is trying to stimulate spending.

The chart above shows how dramatically the base rate changed in recent years. The near-zero rate from 2020 to 2021 was a response to the economic shock of the Covid-19 pandemic — the Bank cut rates to encourage borrowing and spending. The sharp rise from 2022 onwards was a response to surging inflation, as the Bank tried to cool demand and bring prices back under control.

5. Exam Technique: Getting Full Marks on Interest Rate Questions

Interest rate questions on AQA Paper 2 tend to follow predictable patterns. You might be asked to define the term, explain the effect of a rate change, or evaluate a policy decision. Each command word demands a different response structure — and knowing that structure is where marks are won or lost.

Worked example: Writing an Exam-Quality 'Explain' Answer on Interest Rates

Explain one reason why a borrower with a poor credit history is charged a higher interest rate than a borrower with a good credit history. [4 marks]

1. An interest rate is the cost of borrowing money, expressed as a percentage of the amount borrowed. — Starting with a definition signals to the examiner that you understand the concept precisely. This is often worth 1 mark on its own.
2. A borrower with a poor credit history presents a higher risk of default — that is, a greater chance they will fail to repay the loan. — Name the specific factor (risk of default) rather than giving a vague answer like 'they are less trustworthy'.
3. Because the lender faces a higher risk of not being repaid → the lender adds a larger risk premium to the interest rate → this compensates the lender for the possibility of losing money. — Use connectives like 'because', 'therefore', and 'this leads to' to show causation. Examiners reward chains, not lists.
4. As a result, the borrower with a poor credit history pays a higher interest rate than one with a good credit history, where the risk of default is lower and the risk premium is smaller. — Always close the loop by directly answering the question. This confirms your chain of reasoning is relevant.

Answer: An interest rate is the cost of borrowing. A borrower with a poor credit history is more likely to default on their loan. The lender therefore adds a larger risk premium to the rate to compensate for this risk. As a result, the interest rate charged is higher than for a borrower with a good credit history, who presents a lower risk of default and attracts a smaller risk premium.

Across this lesson, you have covered all three specification requirements: what an interest rate is, how it functions for both borrowers and savers, and the range of factors — base rate, risk of default, loan duration, inflation expectations, and competition — that cause different rates to exist across the economy. These ideas connect directly to monetary policy and aggregate demand, which appear throughout Paper 2.