Investment Calculator

What this investment calculator does

It projects what a portfolio becomes when a starting balance and a regular monthly contribution are left to compound at an assumed rate of return. The result separates what you put in from what the growth added, and that split is usually the most instructive part: over long periods the growth quietly overtakes the contributions, which is the entire argument for starting early.

The formula behind it

Two components are added together. The initial sum grows as P × (1 + r)ⁿ, and the stream of monthly contributions grows as PMT × [((1 + r)ⁿ − 1) ÷ r], where r is the monthly return and n the number of months. Contributing 300 a month for 25 years at 7% a year produces roughly 243,000 from about 90,000 of contributions — the remainder is compounding.

How to use this calculator

Enter your initial investment, your monthly contribution, the annual return you expect and the number of years. The result shows the projected balance, the total contributed and the growth earned. Try a range of returns rather than a single figure: modelling 5%, 7% and 9% shows how sensitive the outcome is to an assumption nobody can actually control.

Reading the projection honestly

This is arithmetic, not a forecast. Real markets deliver uneven returns, and a poor decade early on affects the outcome far more than the same decade later. The figure is also in nominal terms — at 3% inflation, money loses roughly half its purchasing power over 25 years, so subtract inflation from your assumed return if you want the result in today's money. Fees matter more than they appear: an annual charge of 1% can consume a fifth of the final balance over a long horizon.