Calculate investment growth with lump sum & monthly contributions — compound interest, inflation-adjusted returns, and year-by-year schedule.
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Whether you're planning for retirement, building a stocks and shares ISA in the UK, contributing to a 401(k) or Roth IRA in the US, or simply growing a lump sum — this investment calculator gives you a complete picture of your money's future value using compound interest.
Enter your initial lump sum, monthly contributions, expected annual return rate and time horizon. The calculator instantly shows your total portfolio value, total contributions, total interest earned, inflation-adjusted real value, and a full year-by-year growth schedule.
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Compound interest means you earn returns not just on your original investment, but on the accumulated interest as well. The more frequently interest compounds (daily vs annually), the faster your money grows. Over 20–30 years, compounding can turn modest monthly contributions into substantial wealth — often described as the "eighth wonder of the world."
In the USA, tax-advantaged accounts include the 401(k) (employer-sponsored), Roth IRA and Traditional IRA — capital gains inside these accounts are tax-deferred or tax-free. In the UK, the Stocks & Shares ISA allows up to £20,000/year of tax-free investment growth. Set the tax rate to 0% when calculating ISA or Roth IRA growth.
The S&P 500 has historically returned around 10% annually before inflation (about 7% after inflation). The FTSE 100 has averaged roughly 7–8%. For diversified global portfolios, 6–8% is a commonly used planning assumption. Past performance does not guarantee future results.
Mathematically, investing a lump sum early typically outperforms because the money has longer to compound. However, regular monthly contributions (dollar/pound cost averaging) reduce timing risk and are more practical for most investors. This calculator supports both simultaneously.
Inflation erodes purchasing power. If your investment grows at 8% but inflation is 2.5%, your real return is about 5.4%. The calculator shows both nominal (face value) and inflation-adjusted (real) figures so you can plan accurately.
Most index funds and ETFs effectively compound continuously. Monthly compounding is standard for most calculations and very close to daily in practice. The difference between daily and monthly compounding on a £10,000 investment at 8% over 20 years is only about £200.
This investment calculator is provided for general informational and educational purposes only. Results are based on hypothetical scenarios using constant rates of return and do not reflect actual market conditions, fees, taxes, or real-world investment performance. Past performance is not a guarantee of future results. FreeUSUKCalculator.com is not a regulated financial adviser. Always consult a qualified independent financial adviser (IFA in the UK, CFP in the US) before making investment decisions. Capital at risk — the value of investments can go down as well as up.
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