Our savings calculator uses the standard future-value-of-annuity formula that banks and financial advisors rely on. Each month, your existing balance earns interest at your entered annual rate (divided by twelve for a monthly rate), and then your monthly contribution is added on top. This process repeats for every month across your chosen time period, so the tool accurately reflects the snowball effect of compound interest — your interest starts earning its own interest, which is exactly what makes long-term saving so powerful.
Because everything happens instantly in JavaScript inside your browser, you can freely experiment: try increasing your monthly contribution by a small amount, or compare a 5% versus a 7% return, and watch the future balance and chart update immediately. This kind of "what-if" exploration is one of the best ways to understand how small, consistent habits compound into large outcomes over years and decades.