Compound interest calculator with monthly contributions

This compound interest calculator estimates how an account could grow when an initial deposit is combined with recurring monthly contributions. It is built for common savings and investing questions: how much a portfolio might be worth after a set number of years, how much of the ending balance comes from deposits, and how much may come from compounded returns. The result is not a forecast or a guarantee. It is a structured way to test assumptions before choosing a platform or account.

The calculation starts with the initial deposit, monthly contribution, time horizon and annual return. The selected compounding frequency is converted into an effective monthly growth rate so the calculator can update the balance month by month. If contributions are added at the beginning of the month, they receive that month's growth. If they are added at the end of the month, growth is applied first and the contribution is added afterward.

The page separates three ideas that are often mixed together: total deposited, estimated growth and projected balance. Total deposited includes the initial deposit plus recurring monthly deposits. Estimated growth is the difference between the projected balance and those deposits. Projected balance is the nominal future value before considering taxes or withdrawals. Showing these values separately makes it easier to understand whether the result is mostly driven by saving more, earning a higher return or allowing more time for compounding.

Inflation is shown as today's purchasing power. A future balance can look large in nominal terms, but inflation can reduce what that amount may buy later. For example, a balance projected ten or twenty years from now can be discounted by an inflation assumption so the user sees an approximate value in today's dollars. This is especially useful when comparing long-term investing goals, retirement planning examples or savings targets that are many years away.

Fees are treated as an annual drag on the return assumption. Platform fees, fund expense ratios and account charges can reduce the amount left to compound. A small annual fee may not feel important in one year, but it can matter over a long horizon because every fee also removes money that could have generated future returns. The fee input is a planning assumption, not a replacement for checking the official provider fee schedule.

A practical example: a user starts with 10,000 dollars, contributes 300 dollars per month, assumes a 6.8 percent annual return and invests for ten years. The calculator shows the projected balance, total deposited, estimated growth and inflation-adjusted value. If the user increases the contribution, deposits become a larger part of the result. If the user extends the time horizon, compounding usually becomes more influential. If fees rise, the projected balance is reduced.

Use the year-by-year table to understand the path, not only the final number. In early years, deposits often explain most of the account value. Later, compounding can become a larger part of the total if the return assumption is positive. The table helps users compare scenarios, explain assumptions and decide whether they need a recurring investing app, a lower-fee broker or a cash account with a more predictable yield.