Understanding CDI: Its Importance in Your Investments
Have you ever seen the term “100% of CDI” in a digital account advertisement or financial application and wondered what it truly means? You’re not alone. The CDI is one of the most frequently mentioned benchmarks in the Brazilian financial market, yet it is often one of the least clearly explained for those just starting to manage their own money.
Understanding the CDI is not just academic curiosity. This index directly influences how much you earn from investments such as CDBs, LCIs, LCAs, fixed income funds, and even the profitability of remunerated accounts. Without understanding what it represents, it’s impossible to compare products, assess whether an offer is good, or identify when an advertised yield is, in practice, unattractive.
In this article, we will explain the CDI from scratch: what it is, how it is calculated, why it varies, how it appears in your investments, and what precautions you should take when using it as a reference. The goal is to give you more clarity to make more informed decisions — not shortcuts or promises of easy returns.
What is CDI
CDI stands for Interbank Deposit Certificate. It is a security issued by financial institutions to raise or lend resources among themselves, usually for very short terms — often just one business day.
Why do banks do this? Due to a requirement by the Central Bank: at the end of each day, all financial institutions must close their cash with a positive balance. When a bank ends the day with more outflows than inflows, it needs to borrow money from another bank that has excess. This loan is formalized through a CDI.
The set of all these operations carried out in a day generates an average rate: the so-called CDI Rate (or DI rate). This rate has become a reference for a large part of fixed income investments in Brazil. The CDI Rate is calculated and published daily by B3 (the Brazilian stock exchange, which also manages the clearinghouse for these operations).
The Relationship Between CDI and Selic
The CDI Rate and the Selic Rate go hand in hand — and this is no coincidence. The Selic is the basic interest rate of the Brazilian economy, set by the Monetary Policy Committee (Copom) of the Central Bank approximately every 45 days. It serves as a reference for the cost of money in the country.
Since the CDI represents the cost of loans between banks, and these banks operate within the same economic environment regulated by the Central Bank, the CDI Rate tends to be very close to the Selic — in practice, it is usually slightly lower, but the difference is marginal.
This means that when the Selic rises, the CDI rises with it; when it falls, the CDI also falls. Therefore, following Copom’s decisions is an indirect way to understand where the CDI is heading.
To check the current Selic and the history of Copom’s decisions, visit the official website of the Central Bank of Brazil (bcb.gov.br). The accumulated CDI Rate can be verified directly on the B3 website (b3.com.br).
How CDI Appears in Your Investments
Most fixed income investments in Brazil use the CDI as an indexer or profitability reference. Here are the most common examples:
CDB (Certificate of Bank Deposit)
The CDB is issued by banks and often pays a percentage of the CDI. An offer of “110% of CDI,” for example, means that the investment will pay 110% of the CDI variation over the period. The higher this percentage, the better the remuneration — in theory. But the percentage must be evaluated along with other factors, such as term, liquidity, and taxation.
LCI and LCA
The Real Estate Credit Letters (LCI) and Agribusiness Credit Letters (LCA) are also usually linked to the CDI, but they have an important feature: they are exempt from Income Tax for individuals. This means that an LCI at 90% of CDI, for example, may be more profitable in practice than a CDB at 100% of CDI — depending on the income tax rate that would apply to the CDB. Always calculate the net return.
DI Funds and Fixed Income Funds
Many investment funds use the CDI as a benchmark (performance reference). A fund that says “aims to exceed 100% of CDI” is signaling that its goal is to yield more than the reference rate. Attention: declared objective is not a guarantee of result.
Remunerated Accounts and Fintech
Various digital accounts and payment wallets remunerate the idle balance based on a percentage of the CDI. Always read the terms: the percentage offered, if there is a grace period, and if there is coverage by the Credit Guarantee Fund (FGC).
The Impact of Income Tax on CDI-Linked Yields
A common mistake when comparing investments is to look only at the CDI percentage without considering taxation. The yields of CDBs, funds, and other CDI-linked products are subject to Income Tax according to the Federal Government’s regressive table:
| Investment Term | IR Rate |
|---|---|
| Up to 180 days | 22.5% |
| From 181 to 360 days | 20% |
| From 361 to 720 days | 17.5% |
| Over 720 days | 15% |
Source: Federal Revenue of Brazil. Always check the current rules at receita.economia.gov.br.
In addition to IR, some products are subject to IOF (Tax on Financial Operations) if redeemed in less than 30 days. The IOF is regressive: it starts at 96% of the yield on the first day and goes to zero from the 30th day.
These costs reduce the net profitability. Therefore, always compare investments based on the net return — after IR and IOF — and not just the gross rate.
Advantages and Limitations of Investing Based on CDI
Like any market reference, the CDI has positive points and points of attention. Here is a balanced overview:
Advantages:
- It is a transparent, public, and verifiable daily rate
- Serves as a clear reference to compare different products
- Investments linked to the CDI tend to keep up with inflation when the Selic is at high levels
- The liquidity of many CDI-indexed products is high (redemption in D+0 or D+1)
Limitations and Risks:
- The CDI varies over time; a high rate today may not remain in the future
- Investments linked to the CDI are not guaranteed regarding future profitability
- In periods of low Selic, the CDI also falls — and the return may fall below inflation
- The announced percentage (e.g., “110% of CDI”) needs to be evaluated in the context of term and taxation
- Lesser-known products may offer higher percentages precisely because they involve greater credit risk of the issuing institution
Speaking of credit risk: when investing in a CDB, you are lending money to the issuing bank. If it fails, the FGC covers up to R$ 250,000 per CPF per institution, with a global limit of R$ 1,000,000 per CPF in a certain period. For the complete FGC rules, visit fgc.org.br.
For a broader view of lower-risk products, also check out our guide Low-Risk Investments in 2026: Where to Start.
How to Use CDI Practically When Evaluating an Investment
Now that you understand what CDI is, see how to apply this knowledge in daily life:
- Check the current CDI Rate on the B3 website before evaluating any offer. This provides the basis for any calculation.
- Identify the CDI percentage offered by the product: 90%, 100%, 120%? The higher, the better the gross remuneration.
- Check the term and liquidity: products with a grace period usually offer better rates. Ensure the term matches your goals.
- Calculate the net return: apply the corresponding IR rate to the term to know how much you will effectively keep from the yield.
- Compare with inflation: high nominal yield does not mean real gain. If the CDI is at 10% per year and inflation is at 8%, the real gain is much smaller than it seems.
- Evaluate the issuer: don’t choose just for the highest rate. Consider the size of the institution and FGC coverage.
- Diversify: don’t concentrate all your reserve in a single product or issuer, even if it seems safe.
Conclusion: CDI as a Compass, Not a Destination
The CDI is a guidance tool, not a guarantee. It indicates the cost of money in the very short term between financial institutions and serves as a ruler to compare fixed income investments. Knowing how to interpret it is a basic skill for anyone who wants to make more informed financial choices.
But knowing the CDI is just the beginning. As important as knowing what it is, is understanding that markets change, rates fluctuate, and no investment is risk-free. The best path is to continue educating yourself, compare products based on real data, and, when necessary, seek professional guidance.
If you’re thinking about organizing your finances more broadly — including decisions like financing a property — it’s worth also checking out the article How Much Do I Need to Earn to Finance a Property? to understand how the interest rate scenario affects other aspects of your financial life.
This content is for educational and informational purposes only. It does not constitute investment recommendation, financial advice, or offer of any product. Each person has a unique financial situation; for investment decisions suitable to your profile and objectives, consult a professional or investment advisor duly registered with the CVM (Securities and Exchange Commission).
