What it's for
Before tackling the real variability of markets, it helps to understand one simple but powerful principle: compound interest. The Basic Simulator answers a concrete question — "if I invest a certain amount today, then contribute (or withdraw) a fixed amount each month, how much will my capital be worth in N years?" — using constant average returns (Global Equities at 10%, Cash at 2%), without the real fluctuations of markets. It's the ideal starting point for beginners: once this mechanism clicks, the Monte Carlo Simulator introduces the real variability of markets using 50 years of historical data.
Your starting scenarios
Four ready-made configurations, one for each typical stage of an investor's life — the same four stages used throughout the site. Load one to get started, then freely edit any value.
Young saver
100% Global Equities£5,000 + £300/month · 20 years
Family in accumulation
80% Equities · 20% Cash£20,000 + £400/month · 20 years
Approaching retirement
60% Equities · 40% Cash£150,000 · no contributions · 20 years
Retired, drawing income
40% Equities · 60% Cash£200,000 · £700/month income · 20 years
Basic Simulator
The preview below reproduces the real layout of the interface with example figures — it isn't a live embed. In the app, the values and chart update in real time as you move the sliders.
Move the sliders for the 4 variables, adjust them to your own scenario, and watch the chart update instantly; discover the power of compound interest, growing value exponentially over time.
a single slider: drag left to draw income, right to contribute
Calculated at constant returns — Global Equities at 10% and Cash at 2% — for illustration only, not a forecast.
Monthly contributions and income are split according to the same Equities/Cash allocation set above.
📊 How to read the results
💰 Final value
The value of the portfolio at the end of the chosen time horizon, calculated at constant (non-probabilistic) returns: Global Equities at 10% a year, Cash at 2% a year — long-term historical averages, not a forecast for the years ahead. The percentage shown below (e.g. +4,916.7%) shows how many times over the invested capital has multiplied.
📈 Growth
The difference between the final value and everything you actually put in (starting capital plus any monthly contributions): this is the pure effect of compound interest, the "engine" quietly working the longer you leave your capital invested.
💸 Income
If the middle slider is set to a withdrawal (monthly income rather than a contribution), this KPI shows the total withdrawn across the whole simulated period. With a positive monthly contribution, on the other hand, this KPI stays blank — there's no income to display.
📉 The chart
The solid line shows the portfolio value year by year; the dashed line shows the capital contributed — that is, what you've actually put in out of pocket (starting capital plus contributions, net of any withdrawals). The growing gap between the two lines over time is, visually, compound interest at work: the more time passes, the further the value curve pulls away from the straight line of amount contributed.
Try the simulator with your own numbers
Move the sliders and watch in real time how starting capital, contributions and time grow your wealth — free, no sign-up required.
Go to the interactive app →