Investment Calculator

Building wealth requires a combination of time, consistent contributions, and compound returns. This investment calculator is designed to help you model different financial scenarios so you can make informed decisions about your future.

Whether you are saving for retirement, a house deposit, or another long-term goal, understanding how contributions and assumed returns interact is useful. This tool offers four modes: projecting future value, calculating required contributions for a specific target, modelling lump-sum growth, and estimating the time needed to reach a financial milestone.

The calculator also includes an inflation assumption so your result is easier to interpret. The headline value shows the projected future amount, while the inflation-adjusted figure estimates its purchasing power in today's money. That distinction matters when planning over long periods.

Suppose you start with GBP 10,000 and invest GBP 400 per month for 20 years with an assumed 6% annual return. Your total contributions would be GBP 106,000, but the projected portfolio value would be much higher because each year's growth can earn returns in later years.

This is why long-term investing is not only about finding the highest return. The amount you contribute, the time you stay invested, and the consistency of the plan often matter more than small differences in assumed annual performance.

An investment projection helps you test whether your current plan is realistic before years pass. If the target is too low, you may need to increase monthly contributions, extend the timeframe, reduce the goal, or accept more investment risk only if it fits your circumstances.

Use conservative return assumptions when planning important goals. A higher assumed return can make the future look comfortable on paper, but it may hide the risk of market downturns, fees, taxes, and inflation.

Increase contributions gradually when income rises, keep fees low, diversify across suitable assets, and avoid interrupting the plan during normal market volatility. Rechecking the numbers once or twice a year is usually more useful than reacting to every market move.

If the inflation-adjusted value is much lower than expected, treat that as a planning signal. It may mean the target needs to be larger, the saving rate needs to rise, or the timeframe needs to change.

The calculator assumes a fixed annual return and regular contributions at the frequency you choose.

Future Value mode projects the portfolio value from an initial amount, contribution amount, return, and time period.

Target Contribution and Years Needed modes work backwards from a target amount, while Lump Sum mode ignores regular contributions.

The inflation-adjusted figure is an estimate of purchasing power, not a separate tax, fee, or market-risk model.

Using an optimistic return assumption without testing a lower one.

Forgetting that fees, taxes, and market volatility are not separate inputs in this calculator.

Mixing monthly, quarterly, and annual contribution assumptions when comparing scenarios.

Use compound interest for a simpler one-off principal, rate, time, and compounding-frequency calculation.

Use savings when the goal is a cash savings target rather than market-style return assumptions.

Use fire when the target is financial independence rather than a standalone investment balance.

Rerun the projection when contribution amount, frequency, target amount, return assumption, inflation assumption, or timeline changes.

Review after income changes, goal changes, or major market moves that alter the assumptions behind the plan.

Keep a note of whether a result is nominal or inflation-adjusted before comparing it with another tool.