Simple Loan Calculators

Simple interest is calculated only on the original principal amount for the entire duration. It does not take into account any interest previously earned or owed. It is commonly used for short-term loans, car finance, and some savings accounts. The formula is SI = P × R × T ÷ 100, where P is the principal, R is the annual rate, and T is the time in years.

The simple interest formula is: SI = P × R × T ÷ 100. P is the principal (the original amount), R is the annual interest rate as a percentage, and T is the time period in years. For example, if you invest £5,000 at 4% per year for 3 years, the simple interest is £5,000 × 4 × 3 ÷ 100 = £600. The total amount after 3 years would be £5,600.

Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. This means your interest earns interest, causing the amount to grow faster over time. It is the standard method used by most savings accounts, investments, and mortgages. The more frequently interest is compounded (daily vs annually), the more you earn or owe.

The compound interest formula is: A = P × (1 + R / (n × 100))^(n × T), where A is the total amount, P is the principal, R is the annual interest rate, n is the number of compounding periods per year, and T is the time in years. The compound interest earned is CI = A − P. For example, £1,000 at 5% compounded monthly for 2 years gives A = £1,000 × (1 + 0.05/12)^24 ≈ £1,104.94.

Simple interest is calculated only on the original principal, while compound interest is calculated on the principal plus any accumulated interest. For the same principal, rate, and time, compound interest always results in a higher total than simple interest. For savers, compound interest is more beneficial. For borrowers, compound interest means you owe more over time if interest is not paid off regularly.

To calculate interest earned on savings, enter your savings amount as the principal, your account's annual interest rate, and the time period. If your savings account compounds interest (most do), choose Compound Interest and select your compounding frequency — typically monthly or daily for savings accounts. The calculator will show the total interest you earn and the final value of your savings.

To calculate interest on a loan or debt, enter the outstanding balance as the principal, the annual interest rate charged by the lender, and the loan term. For simple interest loans (common in car finance and personal loans), select Simple Interest. For credit cards and most mortgages, compound interest applies — select Compound Interest and choose the appropriate compounding frequency (usually monthly).

Compounding frequency refers to how often interest is added to the principal — annually, semi-annually, quarterly, monthly, or daily. The more frequently interest compounds, the faster the balance grows. For example, £1,000 at 10% compounded annually for 1 year gives £1,100, while the same amount compounded monthly gives approximately £1,104.71. For savers, higher frequency is better; for borrowers, lower frequency means less owed.

The Effective Annual Rate (EAR) is the actual annual return or cost of interest once compounding is taken into account. A nominal rate of 12% compounded monthly is equivalent to an EAR of approximately 12.68%, because interest compounds on itself each month. EAR is useful for comparing products with different compounding frequencies on a like-for-like basis. This calculator shows EAR automatically when compound interest mode is selected.

For borrowers, simple interest is better because you only pay interest on the original principal, not on accumulated interest. For savers, compound interest is better because it grows your balance faster. In practice, most financial products use compound interest — mortgages, credit cards, savings accounts, and investments all compound. When comparing products, use the Effective Annual Rate (EAR) to see the true annual cost or return.