Interest Calculator

Interest is the cost of borrowing money or the reward for saving it. This calculator focuses on simple interest, where interest is calculated only on the original principal.

Use it to find the interest owed on a short-term loan, the simple interest earned on savings, the annual rate needed to reach a target interest amount, or the time required at a known rate.

It keeps the calculation deliberately simple. If interest compounds, payments are made on a schedule, fees are charged, or rates can change, use a compound interest, loan payment, APR, or amortisation calculator instead.

If you borrow GBP 2,000 at 6% simple interest for 3 years, the interest is GBP 360. The total amount repaid before any fees would be GBP 2,360.

Simple interest is easier to understand than compound interest because the interest does not earn interest of its own. That makes it useful for quick estimates and short-term scenarios.

Simple interest can help with short-term loans, savings goals, informal repayment plans, and quick comparisons. It is also useful when you need to solve for a missing rate, time period, or interest amount.

For credit cards, mortgages, investments, and savings products that compound or involve regular payments, use a compound interest, APR, loan payment, or amortisation calculator instead.

Simple interest uses the original principal only. It is useful for quick estimates where interest does not earn additional interest.

The calculator can solve for the interest amount, the annual rate needed, or the time needed, depending on which tab you choose.

Because it leaves out compounding, regular payments, fees, and changing rates, it is best treated as a clear baseline rather than a full loan or investment model.

For borrowing decisions, compare the result with APR and loan payment tools before relying on the simple-interest number.

Using simple interest for products that compound monthly, daily, or annually.

Treating a simple-interest result as a complete repayment schedule.

Ignoring fees, taxes, or changing rates when comparing real financial products.

Start here for the simple-interest baseline, then use compound interest when interest earns interest.

Use apr when upfront fees affect borrowing cost, and loan payment when you need a monthly repayment estimate.

If two tools disagree, check whether one includes fees, compounding, payment timing, or a full amortisation formula that this simple-interest calculator omits.

Rerun the calculator when the principal, rate, time period, or target interest amount changes.

For real products, revisit the numbers when a promotional rate ends, a fee appears, or interest starts compounding.

Keep a note of the assumptions you used so you can tell later whether the plan changed because of maths or because circumstances moved.

Simple interest is common on short fixed instruments; compound interest dominates savings accounts and many loans over longer periods.

Check whether the rate quoted is annual and how often interest posts — monthly compounding grows faster than annual at the same headline rate.

For loan decisions, move from interest accrual to full payment schedule with amortisation calculator when term and principal are known.

When comparing savings accounts, check whether the advertised rate is introductory — revert rates can be far lower after the promo window.

Daily accrual on savings adds up faster than monthly crediting at the same advertised rate — check how often interest posts to your account.

On debt, paying early in the cycle reduces interest on some products but not others; read whether interest calculates on daily balance or monthly snapshots.