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Calculate compound interest with regular monthly deposits. See how your savings grow over time with principal, monthly contributions, and compound interest combined.
Adding regular monthly contributions dramatically increases compound interest returns. The formula becomes A = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) − 1) / (r/n)], where PMT is your monthly deposit. For example, starting with $5,000 and contributing $200/month at 7% annual interest compounded monthly for 20 years yields approximately $109,820 — but only $53,000 of that is your actual deposits. The remaining $56,820 is pure interest.
Starting 10 years earlier with the same $200/month at 7% turns $109,820 into roughly $244,690. That extra decade more than doubles your ending balance, even though you only contributed an additional $24,000. This is the true power of compound interest combined with consistent contributions.
$200 per month at 7% annual interest compounded monthly grows to approximately $109,820 after 20 years (with no initial principal). After 30 years it reaches about $244,690. The key is consistency — missing even a few months can significantly reduce your final balance.
Mathematically, a lump sum invested early usually outperforms dollar-cost averaging because the money has more time to compound. However, most people don't have a lump sum available, so monthly contributions are a practical and powerful way to build wealth steadily.
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