Calculate compound interest with monthly contributions — see how your money grows over time.
Compound interest is interest on interest. When a bank pays 1% a month on R$ 1.000,00, the first month earns R$ 10,00 and the second month earns R$ 10,10 — because the R$ 10,00 from the first month is now part of the principal. Over short periods the difference is small; over years it is enormous. That exponential curve is what makes long-term investing work, and what makes long-term debt dangerous.
This calculator takes the initial amount, the annual rate, the compounding frequency and an optional monthly contribution, and shows the total at the end of the period. It also separates what you put in from what interest produced, which is the number that makes the point: on a 20-year savings plan, interest often exceeds the contributions.
The math is the standard compound interest formula with periodic contributions, computed in your browser. No financial advice is implied — the result depends on the rate you type, which in real life fluctuates and is subject to taxes and inflation.
Without contributions: A = P × (1 + r/n)^(nt). With monthly contributions: A = P × (1 + r_m)^m + C × ((1 + r_m)^m − 1) / r_m, where r_m is the monthly rate.
Monthly is the most common for Brazilian investments (CDB, LCI, poupança). Choose the one your investment actually uses.
It is whatever rate you type. To see the after-tax result, type the after-tax rate. This tool does not calculate income tax.
No. The result is nominal. To see real purchasing power, subtract the expected inflation from the rate.
No. The calculation runs entirely in JavaScript on your device.
This calculator is simpler: one rate, one contribution. The investment simulator adds progressive income tax and compares scenarios.
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