Brazil’s Legal Interest Rate for September 2026 is 1.499119% per month, according to Central Bank of Brazil Communication No. 45,850, dated September 1, 2026. That figure, however, is not a rate that automatically applies to every debt. It operates within the scope defined by Article 406 of the Brazilian Civil Code: when interest was not agreed, was agreed without a stated rate, or arises from a legal determination.
In practice, the first question is not “what is this month’s Legal Interest Rate?” but “is my debt a case in which the Legal Interest Rate must be used?” Contracts with an expressly agreed rate, obligations governed by a specific rule, and court decisions setting their own criteria may require different treatment. The monthly figure published by the Central Bank therefore has to be read together with the legal basis of the debt.
What the Central Bank published for September 2026
For September 2026, the Central Bank published three figures used in the methodology:
- Legal Interest Rate (TLm): 1.499119% per month
- Selic factor: 1.01093123
- IPCA factor: 0.9960
The methodology is set out in CMN Resolution No. 5,171/2024. In simplified terms, the monthly Legal Interest Rate is obtained by dividing the Selic factor by the previous month’s IPCA-15 factor and subtracting 1. If the result is negative, the month’s rate is deemed to be zero. The final rate is published to six decimal places.
When the Legal Interest Rate applies to a debt
Article 406 of the Civil Code, as amended by Law No. 14,905/2024, provides three gateways for applying the Legal Interest Rate:
- Interest was not agreed. Interest is due, but the parties did not choose a rate.
- Interest was provided for without a defined rate. The contract or transaction recognizes that interest applies but does not state the percentage.
- Interest arises by operation of law. The legal rule itself points to the legal rate or creates a situation in which legal interest must be calculated.
Law No. 14,905/2024 itself provides concrete examples. For a loan intended for economic purposes, Article 591 now provides that if the interest rate is not agreed, the legal rate in Article 406 applies. For overdue condominium contributions, Article 1,336, paragraph 1, provides for agreed default interest or, if none is provided, interest under Article 406, in addition to the applicable penalty.
The Central Bank also explains that the new benchmark was created to standardize interest in obligations without a defined rate and in cases of non-contractual civil liability. Even so, the starting date for interest and other consequences in a particular case depend on the applicable law, the event giving rise to the obligation, the contract, and, when litigation exists, the court ruling.
When 1.499119% per month should not be applied automatically
| Situation | Practical reading |
|---|---|
| A contract states an express interest rate | The Legal Interest Rate does not automatically replace the agreed rate. The validity of the clause and the specific rules governing that contract must be checked. |
| A specific law establishes another criterion | The obligation’s specific legal regime applies; the special criterion is not replaced by the Legal Interest Rate merely because a monthly figure was published. |
| A judgment or enforceable instrument fixes an index and interest | The calculation must follow the instrument and the applicable procedural rules. The Legal Interest Rate enters only if the legal basis actually refers to it. |
| A bank debt or credit transaction has contracted charges | The monthly Legal Interest Rate is not a universal rate for loans, financing or credit cards. |
| The issue concerns only monetary adjustment | The Legal Interest Rate is interest. Monetary adjustment is a separate component and may have its own index. |
This distinction prevents a common mistake: treating the Legal Interest Rate as a general “interest cap” or as the default rate for every late payment. Article 406 is a reference rule for legally defined situations; it does not automatically erase valid charges established by contract or by special legislation.
Legal interest and monetary adjustment are not the same thing
Law No. 14,905/2024 explicitly separates interest from monetary adjustment. Article 389 of the Civil Code provides that when no monetary-adjustment index was agreed and no index is provided by a specific law, the IPCA variation is used. The Legal Interest Rate in Article 406, by contrast, is the interest benchmark.
CMN Resolution No. 5,171/2024 reinforces this separation: when monetary adjustment is provided for, the Legal Interest Rate must be calculated on the amount after monetary adjustment. It is therefore incorrect to take 1.499119% and treat it, by itself, as resolving every component of a debt.
How September’s 1.499119% is calculated
The formula defined by the CMN is:
TLm = max[(Selic factor ÷ IPCA factor) − 1; 0] × 100
Using the factors published for September 2026, the calculation uses 1.01093123 as the Selic factor and 0.9960 as the IPCA factor. The mathematical result is approximately 1.4991194779%, which the Central Bank rounds to 1.499119% per month.
Importantly, the September factors reflect data from the previous month under the resolution’s methodology. The rate published for a reference month is not simply the annual Selic rate in force that month converted directly into a monthly rate.
Application uses simple interest and calendar-day proration
CMN Resolution No. 5,171/2024 requires simple interest for the Legal Interest Rate, both when accumulating monthly rates and when calculating partial months. In other words, the methodology does not turn the Legal Interest Rate into compound interest through monthly capitalization.
When the period does not cover a full month, the proportional calculation uses calendar days. The daily interest is obtained by dividing that month’s Legal Interest Rate by the number of calendar days in the month, then multiplying by the number of days to be allocated.
September has 30 days, so a hypothetical 15-day period equals half the monthly rate: 1.499119% ÷ 30 × 15 = 0.7495595%.
Three hypothetical examples to understand the mechanism
The examples below illustrate the mathematics only. They do not establish that the Legal Interest Rate is legally applicable to any specific debt.
1. BRL 10,000 for the full month of September
Assume principal of BRL 10,000, with no other component, in a situation where the Legal Interest Rate applies for all 30 days of September. The hypothetical interest would be:
BRL 10,000 × 1.499119% = BRL 149.91.
The amount would reach BRL 10,149.91, disregarding other items that may exist in a real case.
2. BRL 10,000 for 15 days in September
Using calendar-day proration:
BRL 10,000 × 0.7495595% = BRL 74.96.
The decisive issue in a real case is which days actually belong to the period of default or accrual.
3. When monetary adjustment also applies
For illustration only, suppose a BRL 10,000 debt is adjusted by the applicable monetary index and becomes BRL 10,100. If September’s Legal Interest Rate also applies for the full month, interest is calculated on the already adjusted base:
BRL 10,100 × 1.499119% = BRL 151.41.
The hypothetical total would be BRL 10,251.41. The adjustment index in this example is purely illustrative; in a real obligation, it must be determined by the contract, the law or the applicable enforceable instrument.
How to check whether the Legal Interest Rate is correct for your case
- Identify the source of the debt. Does it arise from a contract, condominium fees, a loan, damages, a court judgment or another situation?
- Read the interest clause. Is an express rate stated? Is there only a generic reference to interest?
- Look for a specific rule. Some obligations have their own legislation or parameters defined in a court instrument.
- Separate interest from monetary adjustment, penalties and other charges. They are different components and should not be added or substituted without a legal basis.
- Define the correct period. The initial date of default or interest and the end date can materially change the calculation.
- Calculate month by month. The Legal Interest Rate changes every month. Partial months use calendar-day proration.
The Central Bank provides its Citizen Calculator with a Legal Interest Rate module. The Bank itself notes that the simulation is a reference and does not replace the amount officially demanded by a creditor or a legal analysis of the case.
The September figure answers only part of the question
In September 2026, Brazil’s Legal Interest Rate is 1.499119% per month. Knowing that figure matters, but it produces a correct calculation only when the obligation truly falls within Article 406 and when the accrual period has been determined correctly.
For material debts, contract disputes, court calculations or situations in which it is unclear which rule prevails, the contract, specific legislation and any enforceable court instrument should be reviewed with a qualified professional. The Legal Interest Rate is an official benchmark; whether it applies is a legal question that comes before the arithmetic.
