Compound interestcalculator
Watch money grow, or a debt multiply, with interest on interest. The rate starts at the Selic but is yours to edit, and a fixed notice shows why what matters is the interest above inflation.
- Selic as a starting point
- Editable rate
- Charts and a year by year table
Your numbers
Added at the end of each month.
Selic target
13.75% per year, in force since 09/16/2026. A fixed value, last checked on 10/20/2026, used because the Central Bank could not be read.
1.079% per month
The interest compounds every month. You can type any rate; the Selic is only the starting point.
With a value here, the chart also shows what the money buys in today's prices.
Result
Final balance
R$125,302.74
R$61,000.00 put in and R$64,302.74 earned.
- Total put in
- R$61,000.00
- Interest earned
- R$64,302.74
- Final balance
- R$125,302.74
How it was calculated
- Interest compounds every month. A yearly rate is converted to a monthly one by compounding, so 12% a year is about 0.949% a month, not 1%.
- Deposits and payments happen at the end of each month, after that month's interest.
- With inflation set, the value in today's prices divides the balance by the accumulated inflation, which shows how much buying power the money keeps.
- The income tax option uses the regressive table of fixed income and charges each deposit by how long it stayed invested. It does not include fees or the IOF, and it ignores come-cotas.
- A projection is not a promise: rates change over time, and no investment follows a straight line.
Growth over time
- Put in
- Interest
Show the table
An estimate for information only. Collective agreements, company policy and special cases can change the amounts, so confirm them with your payroll department or an accountant.
How to use the calculator
Step 01
Choose what to see
Investment, debt or goal. Each asks for slightly different fields.
Step 02
Type the amounts
Starting amount, monthly deposit or payment and the period. For a goal there is no period: you enter the amount you want to reach and the calculator tells you how long it takes.
Step 03
Adjust the rate
It comes from the Selic, but you can type any rate, per year or per month. Optionally add inflation and take off income tax.
Step 04
Read the chart
The chart separates what you put in from what interest earned, and the table gives the detail year by year.
What you get
Live Selic, with a plan B
The rate is read from the Central Bank when the page opens. If that is not possible, a fixed value is used and shown with the date it was last checked.
Real interest up front
A fixed notice reminds you that a nominal rate misleads: what makes wealth grow is the interest above inflation.
Three modes
Investment with monthly deposits, debt with or without payments, and goal, which shows how long your starting amount and monthly deposits take to reach the amount you want.
Optional tax and inflation
Take off the regressive fixed income tax and see the value in today's prices.
How compound interest works
With compound interest, each month earns on the balance of the previous month, which already includes interest. That is why time weighs so much: 12% a year is not 1% a month but about 0.949% a month, because interest builds up. The calculator converts the yearly rate to a monthly one that way.
The Selic is the basic rate of the economy and a reference for many fixed income investments. It is nominal, meaning it does not subtract inflation yet. What matters for your wealth is the real interest, the rate above inflation, and that is what the fixed notice and the optional inflation field are for.
In debt mode the calculator shows why expensive debts grow so fast: if the monthly payment does not cover the interest, the balance only rises. In goal mode it tells you how long your starting amount and monthly deposits, growing with interest, take to reach the amount you want.
Income tax on fixed income, by time invested
On CDBs, Tesouro Selic and similar investments, income tax applies only to the gain, and the rate falls the longer the money stays invested. This is the regressive table the calculator uses when you turn the tax on.
| Time invested | Tax rate |
|---|---|
| Up to 180 days | 22.5% |
| 181 to 360 days | 20% |
| 361 to 720 days | 17.5% |
| Above 720 days | 15% |
How much an investment earns with compound interest
An example with R$1,000.00 invested at the start and R$500.00 a month, at 10% a year, with no tax and without discounting inflation. Because interest earns interest, the balance grows faster and faster over time.
| Time | Total invested | Interest earned | Final balance |
|---|---|---|---|
| 1 year | R$7,000.00 | R$370.27 | R$7,370.27 |
| 5 years | R$31,000.00 | R$8,891.13 | R$39,891.13 |
| 10 years | R$61,000.00 | R$41,525.67 | R$102,525.67 |
| 20 years | R$121,000.00 | R$244,857.11 | R$365,857.11 |
| 30 years | R$181,000.00 | R$867,871.06 | R$1,048,871.06 |
Frequently asked questions
Where does the Selic rate come from?
The browser reads the Selic target set by the Copom from the Central Bank website. If that fails, the calculator uses a fixed value kept in the code and shows its effective date and the date it was checked.
Can I change the rate?
Yes, the rate is editable. The Selic is only the starting point. You can type any rate, per year or per month, and return to the Selic with a button.
What is the real interest rate?
It is the interest minus inflation. If an investment pays 12% a year and inflation is 5%, the real rate is about 6.7%. The notice on the calculator shows the historical reference for Brazil.
Is income tax considered?
If you tick the option, the calculator applies the regressive fixed income table to the gains of each deposit, from 22.5% up to 6 months to 15% after 2 years. Fees, IOF and come-cotas are not included.
How does goal mode work?
You enter how much you want to reach, the amount you start with, the monthly deposit (optional) and the rate, and the calculator tells you how long it takes to get there. If you enter inflation, the goal is read in today's prices: the amount to reach rises with inflation month by month, and the deposit stays the same in reais.
Is this a promise of returns?
No. It is a projection with a constant rate. Rates change, and no investment grows in a straight line.
What is the compound interest formula?
M = C × (1 + i)^t: the amount M is the initial capital C times one plus the rate i, raised to the time t, with the rate and the time in the same unit. With monthly deposits, each deposit, made at the end of the month, starts earning from the following month.
What is the rule of 72?
It is a shortcut to estimate in how many years money doubles: divide 72 by the annual rate in percent. At 10% a year it is about 7 years. It is an approximation, and the calculator does the exact math.
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