Calculating net return (rentabilidade)

The advertised rate is the gross return. What actually reaches your account — your net return, or rentabilidade líquida — is what matters, and it is the gross figure minus taxes and fees. Comparing instruments on their gross rates alone is the classic beginner error.

The costs that come out

• Income tax (IR) — applies to CDB, Tesouro and ordinary debêntures (see the next lesson). It does not apply to poupança, LCI, LCA, debêntures incentivadas, CRI or CRA.
• IOF — a tax that only bites on redemptions in the first 30 days (also next lesson).
• Custody/admin fees — e.g. the small annual custody fee on Tesouro Direto bonds charged by the exchange.

A worked comparison

Suppose CDI accumulates 10% over your holding period and you compare two one-year options, with income tax at the 17.5% band that applies after one year (at the time of writing — verify):

A CDB at 100% of CDI, taxable:

Gross gain:  10.0%
Tax (17.5% of the gain): 10.0% x 0.175 = 1.75%
Net gain:    10.0% - 1.75% = 8.25%

An LCI at 90% of CDI, tax-exempt:

Gross gain:  9.0%
Tax: none
Net gain:    9.0%

Despite a lower headline rate, the tax-free LCI wins on net return (9.0% versus 8.25%). This is the whole point of computing net return rather than trusting the advertised number.

The habit to build

Before choosing, always:

1. Identify whether the instrument is taxable or exempt.
2. Apply the correct tax band for your holding period.
3. Subtract any fees.
4. Compare the resulting net figures — never the gross ones.

The next lesson gives you the exact tax tables to plug in.