Project the growth of your investment over time with regular contributions and compound returns.
Rates as of Q2 2025 (example)
An investment calculator projects how an investment portfolio could grow over time, based on an initial lump sum, regular monthly contributions, and an assumed average annual return. Unlike a savings account, investments such as stocks, funds, and shares don't have a guaranteed rate of return — this calculator shows a projection based on an assumed average return, which is useful for long-term planning but isn't a guarantee of actual results.
This calculator compounds your investment monthly: each month, growth is calculated on the current portfolio value and added to it, then your monthly contribution is added on top — so the following month's growth is calculated on a larger base. This is a simplified model — real investment returns fluctuate month to month rather than growing at a smooth, constant rate.
Formula: Each month: Portfolio Value = Portfolio Value × (1 + monthly return) + Monthly Contribution, where monthly return = Annual Return ÷ 12 ÷ 100. This repeats for the total number of months (years × 12).
Example: Starting with a £10,000 initial investment, contributing £300 per month, at a 6% average annual return (example rate — enter your expected rate) over 15 years, the projected portfolio value is roughly £111,800. Of that, £64,000 comes from your contributions (£10,000 initial plus £54,000 over 15 years of £300/month), and about £47,800 is investment growth. (Note: all figures in this example are for illustration purposes only and are not guaranteed — actual investment returns fluctuate and can be negative.)
Many UK investors hold investments within a Stocks & Shares ISA, which shelters investment growth and dividends from Income Tax and Capital Gains Tax up to the annual ISA allowance — making it a popular choice for long-term investing alongside (or instead of) a General Investment Account, which doesn't have the same tax advantages. Regular monthly contributions, as modelled here, also benefit from "pound-cost averaging" — buying more units when prices are low and fewer when prices are high, which can smooth out the impact of market volatility over time, though it doesn't guarantee better returns than investing a lump sum. Higher expected returns are generally associated with higher risk (such as a higher allocation to equities versus bonds or cash) — this calculator's smooth, constant-return projection doesn't reflect the volatility that real investments experience, including the possibility of losses in any given year.
No specific rate is guaranteed — the default is an example only. Historical average returns for diversified portfolios have varied significantly depending on asset allocation (e.g., equities versus bonds), time period, and fees. Future returns aren't guaranteed and could be higher or lower, including negative in some years.
No. This calculator projects growth based on the return rate you enter, without separately deducting platform fees, fund management charges, or trading costs. These fees reduce your actual net return, so consider using a return assumption net of expected fees, or factor fees in separately.
No. This calculator shows growth before tax. In the UK, investments held in a Stocks & Shares ISA grow free of Income Tax and Capital Gains Tax (up to the annual ISA allowance for new contributions), while investments in a General Investment Account may be subject to these taxes on gains and dividends above relevant allowances.
Pound-cost averaging refers to investing a fixed amount regularly (e.g., monthly), which means you buy more units when prices are lower and fewer when prices are higher, averaging out your purchase price over time. It's a natural result of regular contributions, like those modelled in this calculator, though it doesn't guarantee better returns than investing a lump sum upfront.
This calculator uses a constant assumed annual return for simplicity, which makes long-term projections easier to understand. In reality, investment values fluctuate — sometimes significantly — from month to month and year to year, even if the long-term average return matches the assumption used.
This calculator supports both — enter your lump sum as the initial investment and any ongoing contributions as the monthly amount. Whether a lump sum or regular contributions work out better depends on market timing, which can't be predicted — many investors choose regular contributions partly for the discipline and cash-flow benefits, regardless of which approach might mathematically outperform.
Disclaimer: The information, rates, and figures provided on this page are for educational and illustrative purposes only and do not constitute financial advice or a guarantee of investment returns. The default annual return is a sample value and does not reflect the performance of any specific investment, fund, or strategy. The value of investments can go down as well as up, and you may get back less than you invested. Past performance is not a reliable indicator of future results. Always consult a qualified financial adviser before making investment decisions.