Dados B3 › Compound interest calculator

Compound interest calculator

What your money becomes with compound interest: fill in the four fields and click Calculate.

Simulation. Constant rate over the whole term, no costs. Not investment advice, and we do not store what you type.

How the calculation works, step by step

M = P·(1 + i)ⁿ + PMT·((1 + i)ⁿ − 1) / i

1. Monthly rate. If you typed an annual rate, the calculation uses the equivalent monthly rate: i = (1 + a)^1/12 − 1. Example: 12% a year is 0.9489% a month. If you typed a monthly rate, it uses that rate.
2. The initial amount. P earns for n months: P·(1 + i)ⁿ.
3. The contributions. Each one goes in at the end of the month and earns for the time left. Added up: PMT·((1 + i)ⁿ − 1) / i.
4. The interest. Interest = final value − total invested (P + PMT·n).
5. In today's money. Divide the final value by (1 + inflation)^years.

Worked examples

R$ 1,000 at 12% a year, for 1 year, no contribution: 1,000 × 1.12 = R$ 1,120.00. That is R$ 120.00 of interest.

Only contributions of R$ 100 a month, at 12% a year, for 1 year: 100 × (1.12 − 1) / 0.009489 = R$ 1,264.65. You invested R$ 1,200.00; the interest is R$ 64.65. Open this example.

Where the official rates come from

Today's Selic: the target set by Copom, published by the Central Bank (SGS series 432). IPCA: 12-month inflation, from IBGE (SIDRA, table 1737). Both come from our Macro section and are updated every night. IPCA + X% uses (1 + IPCA) × (1 + X) − 1. The calculation assumes a constant rate over the whole term.

What about the CDI? The CDI usually sits slightly below the Selic. It is computed by B3 and not published here; use the Selic as a reference.

Frequently asked questions

What is compound interest?

It is interest on interest. Each month the return is added to the balance and starts earning too. That is why the curve bends upward over long terms.

What is the compound interest formula?

M = P(1 + i)^n + PMT((1 + i)^n - 1)/i. P is the initial amount, PMT the monthly contribution, n the number of months and i the monthly rate. With no contribution, it is just M = P(1 + i)^n.

How do I turn an annual rate into a monthly rate?

Use i = (1 + annual rate)^(1/12) - 1. 12% a year is 0.9489% a month, not 1%. Dividing by 12 overstates the result.

How much does R$ 1,000 earn at 12% a year in one year?

R$ 1,120.00 gross: R$ 120.00 of interest. With the regressive income tax at 17.5% (365 days), the net value is R$ 1,099.00.

Does the calculator deduct income tax?

Only if you tick the box. It uses the regressive table for fixed income: 22.5% up to 180 days, 20% up to 360, 17.5% up to 720 and 15% above. It is a simplified estimate.

For developers

The same calculation as JSON, open and with no key: GET /calculadoras/juros-compostos.json?inicial=1000&aporte=100&prazo=10&taxa=12 (it also takes unidade, modo, juro_real, ipca, inflacao and ir). Invalid input answers 400 with the reason.

Another calculator: DI future (PU and basis point).

Numbers on this page are live. Data version 2026-11-03-delistadas-proventos-cvm · page generated 2026-11-03 23:36 UTC. If this does not match /saude, you are reading a cached copy.