See how your money grows over time
Compound interest is interest earned on both your original deposit and previously earned interest. Unlike simple interest, compound interest causes exponential growth over time. A 25-year-old investing $200/month at 7% will have ~$525,000 by 65. Starting at 35 with the same amount yields only ~$243,000. Use the savings goal calculator to set a specific target, and track your subscriptions to find money to invest.
The math behind compound interest is straightforward: each period, interest is calculated on your total balance — original deposits plus all previously earned interest. In year one, $10,000 at 7% earns $700. In year two, you earn 7% on $10,700, which is $749. By year ten, you are earning over $1,300/year on that same initial deposit. The growth accelerates because your interest earns its own interest.
This is why compound interest is often called the most powerful force in personal finance. Small, consistent contributions early in life can outperform much larger contributions made later. The calculator above lets you see this effect with your own numbers.
Interest can compound annually, monthly, daily, or even continuously. The more frequently it compounds, the faster your money grows — though the difference narrows as frequency increases.
Annual compounding: $10,000 at 6% compounded annually grows to $17,908 after 10 years. Interest is calculated once per year on your balance.
Monthly compounding: The same $10,000 at 6% compounded monthly grows to $18,194 after 10 years — an extra $286. Most savings accounts and CDs use monthly compounding. Each month, 0.5% (6% divided by 12) is applied to your current balance.
Daily compounding: Compounded daily, the result is $18,221 — only $27 more than monthly. High-yield savings accounts often advertise daily compounding, but the practical difference from monthly is minimal for most savers.
The takeaway: monthly vs. daily compounding barely matters. What matters far more is the interest rate itself and how consistently you contribute. Moving from a 0.5% checking account to a 4.5% HYSA has 9x more impact than switching from monthly to daily compounding at the same rate.
One of the most important lessons in compound interest is that time beats money. Starting earlier with less almost always outperforms starting later with more.
Scenario A: Start at 25, invest $200/month at 7% for 40 years. Total contributed: $96,000. Balance at 65: approximately $525,000. Your money grew to over 5x what you put in because compounding had four decades to work.
Scenario B: Start at 35, invest $400/month at 7% for 30 years. Total contributed: $144,000. Balance at 65: approximately $487,000. Despite contributing $48,000 more out of pocket, you end up with roughly $38,000 less. The missing decade of compounding cannot be recovered by doubling your contributions.
Scenario C: Start at 25, invest $400/month at 7% for 40 years. Total contributed: $192,000. Balance at 65: approximately $1,050,000. Starting early and contributing more is the ideal combination, but if you have to choose one, start early.
If you are getting a late start, do not be discouraged — the best time to start is still today. Use the paycheck budget calculator to find room in your budget, and cancel unused subscriptions to redirect that money into investments. Even an extra $50/month invested at 7% grows to over $60,000 in 30 years.
Savings Goal Calculator — Monthly savings needed for a specific goal
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