The investment calculator shows you how any investment — stocks, ETFs, index funds, savings bonds — grows over time with compound returns and regular contributions. Enter your starting amount, how much you add each month, your expected annual return, and the investment horizon.
Regular contributions have an enormous impact on final portfolio value. Adding $500/month to a
Historical stock market returns: S&P 500 averages ~10% nominally (~7% inflation-adjusted) over 30-year periods. Bond portfolios average 4–5%. A 60/40 stock-bond mix averages 6–7%.
Use this calculator when choosing between investment platforms with different fee structures, when deciding how much to contribute to a pension or ISA, or when setting a long-term financial target. It is particularly useful for illustrating the true cost of delaying investment: model the same monthly contribution starting today versus starting in 5 years and compare the outcomes at retirement age.
Assuming a steady return rate is the most significant model simplification. Real investment returns are lumpy and sequence-dependent — two portfolios with the same average return but different sequencing of gains and losses can produce very different outcomes, particularly when withdrawals are involved. Use this calculator for directional planning, not precise prediction. A second common error is using pre-fee, pre-tax return rates: a fund returning 8% with a 1.5% annual fee and 40% tax on gains is effectively returning approximately 3.9% net — a number that produces very different projections.
An investor puts £500/month into a stocks and shares ISA for 25 years at an average 6% annual return. Total contributions: £150,000. Final value: approximately £346,000 — £196,000 of which is investment growth. Switching to a platform with a 1% lower annual fee saves approximately £28,000 over the same period through reduced fee drag. Both numbers — the growth opportunity and the fee impact — are visible in one calculator run.
Investment Future Value Formula
FV = P×(1+r)^n + PMT×[((1+r)^n − 1)/r × (1+r)]
P = starting amount, r = periodic return rate, n = number of periods, PMT = periodic contribution. Multiply PMT term by (1+r) for start-of-period contributions.
Invest $5,000 today with $300/month at 8% annual return for 15 years.
Result: Total portfolio value after 15 years: ~
7–10% annually for a diversified equity portfolio (historical average). Use 7% for conservative projections, 10% for optimistic. Bonds: 4–5%. Cash: 0–2%.
Any consistent amount helps. $200/month at 8% for 30 years grows to $272,000. Increase contributions whenever income increases.
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