Treasury Bills: What they are and How they work (2026)

June 30, 2026

Treasury Bills are one of the safest and most popular investment instruments in Spain, especially during times of economic uncertainty. Issued by the State, they offer a low-risk form of fixed income, which is ideal for conservative investors.

In this article, you will find everything you need to know about them. We will explore in detail what they are, how they work, their profitability in 2026, how to invest in them, and how they compare to other financial products.

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What are Treasury Bills and what are they used for?

Treasury Bills are short-term public debt securities issued by the Spanish Public Treasury. They represent a loan that investors make to the State, which commits to returning the capital plus a yield within a specified period (3, 6, 9, or 12 months).

Their main characteristics are their short terms, fixed profitability, they are bought at a discount and 100% of the value is received at maturity; and they are low-risk, as they are backed by the Spanish State, which makes them very secure.

Treasury Bills serve to diversify the investment portfolio, being ideal for investors seeking security, for good liquidity, as they can be sold on the secondary market before maturity, and they offer protection against inflation, since in some cases, they can outperform inflation depending on interest rates.

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Advantages

Maximum security and low default risk

Treasury Bills are backed by the Spanish State, which means the risk of non-payment is practically zero; they are considered one of the safest investments available in the market. This makes them an ideal option for conservative investors or those looking to protect their capital.

Flexibility in investment terms

One of the major advantages of Treasury Bills is the variety of terms available. Investors can choose between maturities of 3, 6, 9, or 12 months, which allows them to adapt the investment to their personal financial needs.

Liquidity in the secondary market

Although designed to be held until maturity, Treasury Bills can be sold on the secondary market if the investor needs liquidity sooner. This provides additional flexibility compared to other fixed-income products, but the selling price on the secondary market will depend on interest rate movements.

Accessibility for small investors

The minimum investment for Treasury Bills is 1,000 euros, making them accessible to a wide range of investors. Furthermore, commissions are typically not applied when purchased directly through the Public Treasury, which reduces the costs associated with the investment.

Commission exemption for direct purchase

If you decide to buy Treasury Bills directly through the Bank of Spain or the Public Treasury portal, you will not pay purchase or custody fees.

More favorable taxation than other products

Although the interest from Treasury Bills is subject to income tax (between 19% and 23%, depending on the yield), their tax treatment is simpler than that of other instruments like investment funds. Furthermore, as a fixed-income product, they do not generate unexpected tax surprises.

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Who issues them and how do they work?

Treasury Bills are issued by the Spanish Public Treasury, an entity under the Ministry of Economy and Finance. Their primary function is to finance the State's short-term liquidity needs.

The Public Treasury organizes regular auctions (generally monthly) where investors can bid for the Bills. These auctions are usually announced in advance on the official Treasury portal.

In the allocation mechanism, Bills are assigned through a competitive and non-competitive auction system. In competitive bids, large investors such as banks or funds specify the price they are willing to pay. In non-competitive bids, small investors accept the average price resulting from the auction.

Bills are purchased below their nominal value. For example, if you invest 970 euros in a Bill with a nominal value of 1,000 euros, you will receive the full 1,000 euros at maturity, earning a profit of 30 euros.

At the end of the term, the State repays the capital plus the implicit interest, which is the difference between the purchase price and the nominal value.

If you need liquidity before maturity, you can sell your Bills, although the price will depend on interest rate fluctuations.

What yield are they offering in 2026?

The yield of Treasury Bills continues to be influenced by the European Central Bank (ECB) interest rates. According to recent data, 3-month Bills offer a yield of between 2.5% and 3%, 6-month Bills between 3% and 3.5%, and 12-month Bills between 3.5% and 4%.

While not the highest yields in the market, their security makes them attractive compared to bank deposits.

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How to Invest in Treasury Bills: Step-by-Step

Investing in Treasury Bills is a straightforward process, but it requires following some key steps.

Open an account with the Bank of Spain or an authorized intermediary

If you want to buy directly, you'll need an account with the Bank of Spain, which is free, or you can also do so through commercial banks or authorized brokers, although these may charge commissions.

Check the auction calendar**.**

Auction dates are published on the Treasury website. There is usually at least one auction per month for 3, 6, and 12-month Treasury Bills.

Decide on the term and amount to invest

You must choose between terms of 3, 6, 9, or 12 months. The minimum is 1,000 euros, and investments must be in multiples of this amount.

Submit your application before the auction closes

You can do this online if you have a Treasury account or through your bank. You must indicate whether you are participating in a competitive or non-competitive bid (which is more recommended for small investors).

Wait for the allocation

After the auction, the results are published, the Treasury Bills are allocated, and the money is automatically debited from your account.

Payment at maturity

At the end of the term, you receive 100% of the face value in your account, and if you prefer to sell early, you can do so on the secondary market.

Tips for successfully investing in Treasury Bills

Compare returns before investing

You can review historical yields from past auctions on the Public Treasury website, keeping in mind that 12-month Treasury Bills usually offer better returns than 3 or 6-month ones.

Diversify your returns

If you invest a large amount, you can spread it across different terms (e.g., 50% for 3 months and 50% for 12 months). This gives you greater flexibility to take advantage of potential interest rate hikes.

Consider the secondary market if you need liquidity

If an emergency arises, you can sell your Treasury Bills on the market, although the price will vary depending on demand.

Evaluate alternatives if you're looking for higher returns

If interest rates are very low, compare them with bank deposits or corporate bonds.

Stay informed about interest rate developments

It's important to pay attention because if the ECB raises rates, new Treasury Bills could offer better returns.

Treasury Bills vs. Other Fixed-Income Instruments

Treasury Bills are just one of many fixed-income options available.

Bank deposits often offer similar or higher returns, but they also typically come with penalties for early withdrawal.

Bonds (2 to 5 years) and Debentures (10 to 30 years) offer higher returns but with greater interest rate risk. Treasury Bills are more liquid and less sensitive to rate hikes.

Fixed-income investment funds diversify risk but have fees and do not guarantee capital, whereas Treasury Bills are more transparent and predictable.

Corporate promissory notes offer higher returns but with greater risk, as they depend on the company's solvency.

In summary, Treasury Bills are ideal for conservative investors seeking security and liquidity, while other products, such as bonds or funds, may be better for those willing to accept more risk in exchange for higher returns.

Frequently Asked Questions (FAQs)

What are the risks of buying Treasury Bills?

The risk is minimal, as they are backed by the State. However, if interest rates rise, their value in the secondary market may decrease.

How are Treasury Bills taxed?

Interest is subject to 19-23% income tax (IRPF), depending on the return obtained.

What is the most profitable term for investing in Treasury Bills?

It depends on interest rates. 12-month Treasury Bills typically offer better returns.

How much does a Treasury Bill cost in Spain?

The minimum is 1,000 euros, and they are purchased in multiples of this amount.

What guarantee do Treasury Bills have?

They are guaranteed by the Spanish State, making them one of the safest investments.

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Conclusion

Treasury Bills are an excellent option for investors seeking security and liquidity. Although their profitability is not the highest in the market, their low risk makes them ideal for protecting short-term capital.

Sergio Navarro

Expert in blockchain, investments, and personal finance

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