Free tools

Use the compound growth calculator when the question is how big does this get. It compounds annually, adds your contribution at the end of each year, and splits the result into what you put in versus what the market produced. That split is the thing worth watching: the point where growth overtakes contribution is the whole argument for starting early.

Use the inflation-adjusted simulator when the question is what will it actually buy. It compounds monthly and then runs a second line showing the same balance discounted by inflation. Almost every projection you will see online shows only the first line. The gap between the two is usually larger than people expect — over thirty years at 3% inflation, a pound keeps about 40% of its purchasing power.

They will not agree to the penny, and that is expected rather than a bug: monthly compounding runs slightly ahead of annual at the same headline rate. If you want one sentence to decide by — the calculator is for setting a target, the simulator is for sanity-checking it.

Neither predicts anything. The returns are numbers you choose, and no product guarantees them. Neither deducts fees or tax, so subtract those from the rate you enter rather than reading the output as net — a 1% annual fee against an 8% return removes roughly a quarter of the final total over thirty years, which is not intuitive and is the single most common way these projections flatter reality.

Both also assume a steady return, and markets deliver the same average as an unpredictable sequence. The order matters, severely so once you are withdrawing.

If you want the options actually available where you live, with real yields, fees and lock-in periods, compare them here.