Compound Interest Calculator with Monthly Contributions

Project long-term growth when you invest a set amount every month

How much can monthly investing grow over time?

Investing $300 a month at 7% annual return compounds to roughly $124,000 after 20 years, even though you only deposit $72,000. The compound interest calculator applies the future value of an annuity formula so you can adjust contribution size, rate, and frequency to match your plan.

Breaking down the future value formula

The calculator multiplies your monthly contribution by the compound growth factor: FV = P × [((1 + r/n)^(n×t) - 1) / (r/n)], where r is the annual rate, n is compounding periods per year, and t is years invested.,Adding an initial principal simply adds another future value component that grows independently alongside your contributions.

Comparing contribution cadences

Monthly contributions keep cash working in the market more consistently than quarterly or annual deposits.,Bi-weekly or weekly investing can produce marginally higher balances when your broker supports automatic transfers without extra fees.,Use the schedule output to visualize how different cadences accumulate over identical time horizons.

Adjusting for inflation and risk

Overlay inflation assumptions to translate your future balance into today’s purchasing power.,Run optimistic and conservative rate scenarios to account for market volatility. A blended return range keeps expectations realistic.,Layer tax-advantaged accounts (401(k), IRA) into the plan to retain more of your compound gains.

Consistency tips for monthly investors

• Automate transfers right after payday to prevent spending the cash you intend to invest.
• Schedule annual "raise your savings" reviews to bump contributions alongside income growth.
• Rebalance portfolios yearly so contributions maintain your target asset allocation.

Plan other parts of your financial picture

Compound Interest Calculator

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Visualize monthly versus annual contributions with interactive charts.

Future Value Calculator

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Project single deposits or irregular cash flows alongside monthly investing.

Retirement Calculator

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Translate your savings trajectory into retirement income projections.

Turn monthly habits into long-term wealth

Small monthly contributions compound into significant balances when you stay disciplined. Use the calculator to test scenarios, document your plan, and revisit it every year to keep growth on track.