See how your money grows over time. Add regular contributions, pick a compounding frequency, and watch interest do the heavy lifting.
| Year | Contributions | Interest | Balance | Split |
|---|---|---|---|---|
| Year 1 | $12,400 | $816 | $13,216 | |
| Year 2 | $14,800 | $1,864 | $16,664 | |
| Year 3 | $17,200 | $3,162 | $20,362 | |
| Year 4 | $19,600 | $4,727 | $24,327 | |
| Year 5 | $22,000 | $6,578 | $28,578 | |
| Year 6 | $24,400 | $8,737 | $33,137 | |
| Year 7 | $26,800 | $11,226 | $38,026 | |
| Year 8 | $29,200 | $14,068 | $43,268 | |
| Year 9 | $31,600 | $17,288 | $48,888 | |
| Year 10 | $34,000 | $20,916 | $54,916 |
Contributions Interest
Compound interest is what happens when the interest you earn on a deposit starts earning interest of its own. Instead of growing in a straight line, your balance accelerates: each new period, you earn interest on a larger base than the period before. Over a long enough horizon, the curve gets steep — which is why patient savers consistently out-earn last-minute ones, even when they contribute less in total.
The calculator above lets you experiment with the four levers that drive that curve: how much you start with, how much you keep adding, the rate you earn, and how long you let the money work. Small changes to any one of them — especially the rate and the time — produce big shifts in the final balance.
The textbook formula for a one-time deposit with no further contributions is:
When you also add a recurring contribution, there's a second term that compounds the stream of deposits. This calculator handles both at once, month by month, so the figures stay accurate no matter which compounding frequency you pick.
Start by entering the amount you have today as the initial deposit. If you don't have a lump sum yet, leave it at zero and just use the monthly contribution. Set a realistic annual interest rate — for context, a broad stock-market index has historically returned around 7–10% per year on average, while a high-yield savings account sits closer to 3–5%. Pick a time horizon that matches your goal — retirement, a house, a college fund — and a compounding frequency (most real accounts compound monthly or daily).
The results panel updates the moment you hit Calculate, and the year-by-year breakdown shows you exactly when interest starts overtaking contributions. That crossover point is the magic of compounding made visible.
Compound interest is interest calculated on the initial principal plus the interest that has already been added to it. In other words, you earn interest on your interest, which makes your money grow faster over time than simple interest, where interest is only ever calculated on the original amount.
The standard formula is A = P(1 + r/n)^(nt), where A is the final amount, P is the principal, r is the annual interest rate (as a decimal), n is the number of times interest compounds per year, and t is the number of years. This calculator extends that formula to also include regular monthly contributions.
Simple interest only ever pays you interest on your original deposit. Compound interest pays you interest on your deposit plus every dollar of interest that has already been credited to your account. Over decades, the gap between the two can be enormous — this is why compounding is often called the most powerful force in finance.
The more frequently interest compounds, the more you earn. Monthly compounding produces more growth than annual compounding at the same nominal rate, and daily compounding is slightly better still. In practice, the difference between monthly and daily compounding is small — what matters most is the rate, the time horizon, and how much you keep adding.
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