Work Out Your Investment Growth with Our Compound Interest Calculator
This compound interest calculator helps you forecast how your savings or investments will grow over time, accounting for interest earned on both your initial amount and accumulated returns.
How to use: Compound Interest Calculator | Investment Growth UK
Compound interest works by calculating returns not just on your original capital, but on the interest you've already earned—this is why it's often called 'interest on interest'. The calculation uses the formula: A = P(1 + r/n)^(nt), where P is your principal amount in pounds, r is the annual interest rate as a decimal, n is how often interest compounds per year, and t is the number of years. Most savings accounts and investment bonds in the UK compound annually or monthly. The more frequently interest compounds, the faster your money grows. Even small differences in interest rates can create substantial differences over decades, which is why understanding this principle is crucial for long-term wealth building.
Consider a practical example: if you invested £10,000 in a UK stocks and shares ISA earning an average annual return of 6%, after 20 years you'd have approximately £32,071. By contrast, leaving that same £10,000 in a standard savings account at 4% would give you roughly £21,911—a difference of over £10,000. Another scenario: contributing £5,000 annually to a pension from age 25 to 65 with 5% annual growth would accumulate to around £681,000 before tax implications. Even starting with smaller amounts makes a difference; a junior savings account with £2,000 at 3.5% compound interest grows to £3,815 over 15 years—useful for children's education funds.
When using this calculator, ensure you're inputting realistic interest rates for your chosen investment type—ISAs, Premium Bonds, and direct equity investments have different growth profiles. A common mistake is forgetting to account for tax on interest earned; remember that savings interest above £1,000 annually becomes taxable for basic rate taxpayers. Also, inflation erodes purchasing power, so whilst your pot might look impressive in nominal terms, consider whether the real (inflation-adjusted) return meets your goals. Update your calculations annually as rates change, and don't forget to factor in any regular contributions you're making alongside your initial investment.