There are two methods for dividing the number of days in a year when calculating margin interest (margin trading) - Photo: HUU HANH
Many investors call this a "blind spot" because few people pay attention to it, depending on the conversion of the number of days in a year. Although the amount is not large for individuals, with large loan volumes, many entities collect a significant difference.
The unknown factor in calculating margin loan costs.
Compared to the end of 2025, margin interest rates at many securities companies have increased by about 0.5 - 1 percentage point. A survey by Tuoi Tre Online shows that the common interest rate fluctuates around 12.5 - 14% per year. This interest rate chart creates a sense of a relatively clear and easily comparable cost level among securities companies.
However, even with the same 14% annual return, the actual cost an investor pays can vary depending on the convention of the number of days in a year (360 or 365 days) and how interest rates are converted. This detail directly affects the cost of capital, but not all investors pay attention to it.
Technically, the 360-day calculation method isn't wrong, but it can create discrepancies. For example, a 1 billion VND margin loan for 30 days at an annual interest rate of 14% would cost approximately 11.51 million VND in interest calculated over 365 days. If calculated over 360 days, the interest would be 11.67 million VND. This means the investor pays an additional 160,000 VND, equivalent to a cost increase of about 1.4%.
In fact, securities companies simultaneously apply both of the above calculation methods. Securities companies such as TCBS, HSC, LPBS, MBS, etc., apply the 365-day calculation method, in line with the spirit of Circular 14/2017 of the State Bank of Vietnam, which has been applied to credit institutions since 2018.
Some other units such as ACBS, PHS, Mirae Asset, VPS... or in some of SSI's preferential formulas apply the 360-day calculation method.
What do the securities firms say?
The director of a securities company (who requested anonymity) said he was quite surprised that the market still has two parallel methods of calculating interest. According to him, the 365-day approach is closer to reality. Essentially, margin interest rates should be calculated daily to accurately reflect costs at any given time, as investors' outstanding debt fluctuates constantly and they rarely hold long-term loans.
Responding to Tuoi Tre Online, a representative from SSI Securities said that securities companies are currently implementing a common roadmap, closely following the requirements of the regulatory authorities.
Ensuring transparency and preventing customer disadvantage, SSI also follows a general direction, guaranteeing clarity and consistency throughout the implementation process.
VPS Securities affirms that the regulation of margin loan interest rates based on a 360-day base year is in accordance with current legal regulations.
Specifically, the 2015 Civil Code stipulates that the definition of a year as equivalent to 365 days is a convention used in cases of converting time units and is considered a default. At the same time, the law also recognizes the principle that parties have the right to agree on the method of calculating interest and determining the time limit in civil transactions.
The interest rate on margin trading loans offered by this institution, whether calculated based on a 360-day or 365-day year, falls within the regulated ceiling of 20% per annum. Therefore, VPS states that the interest rate on margin trading loans and the calculation of the loan term based on 360 days are legal.
Choosing a 360-day basis is merely a technical conversion method in calculations and does not change the fundamental nature of the interest rate agreed upon with the customer.
It is necessary to convert to a unified calculation method.
Mr. Bui Hoang Hai, Vice Chairman of the State Securities Commission, stated that margin trading loans are determined based on agreements between securities companies and clients, and in accordance with the provisions of the Civil Code.
Specifically, Article 463, which regulates loan agreements, allows the parties to agree on the content of the loan agreement, including the loan term. Article 468 stipulates that the agreed interest rate shall not exceed 20% per year of the loan amount, including the loan term, unless otherwise provided by relevant laws.
Article 145 stipulates that the calculation of time limits shall be applied according to the provisions of the Civil Code, unless the parties agree otherwise or the law provides otherwise.
Therefore, the application of 360-day or 365-day terms by securities companies is subject to agreement between the parties, provided that the method of calculating interest is clearly stipulated in the contract and complies with relevant legal regulations.
relate to.
Globally , conventions for calculating the number of days in a year to determine interest rates are formed from market practices and standardized, recognized by international organizations. These are not legally binding regulations, but rather technical conventions widely used in pricing and calculating interest rates.
In the US, money market instruments and commercial loans typically use a 360-day basis. Meanwhile, derivative contracts and international loans may use a 365-day basis.
In Singapore, the choice of date calculation convention depends on the type of financial product and market practices, and is determined in the specific terms of the contract.
Mr. Nguyen Quang Huy, CEO of the Finance and Banking Faculty at Nguyen Trai University, believes that some parties choose the 360-day period to align with international practices and for operational convenience.
However, with the same quoted interest rate, calculating the cost over 360 days will result in a higher actual cost compared to 365 days. This difference may not be significant in the short term, but it can accumulate considerably for investors who frequently use margin or operate on a large scale.
According to Mr. Huy, instead of mandating a rigid standard, the regulatory body could consider requiring securities companies to clearly disclose actual costs, converted to a common standard, or to disclose effective interest rates, so that investors can easily compare them.
Should we just leave this "grey area" as it is?
Speaking to Tuoi Tre Online, lawyer Truong Thanh Duc, Director of ANVI Law Firm, said that applying the 360-day interest calculation method deviates from the time limit stipulated in the Civil Code.
Previously, the State Bank of Vietnam also used the 360-day period, but later revised it to 365 days to align with the Civil Code.
According to the lawyer, securities companies applied the old regulations of the State Bank of Vietnam but did not supplement them according to Circular 14/2017, because there was no mandatory regulation.
Lawyers argue that the Ministry of Finance and the State Securities Commission have not yet issued clear regulations, possibly because the issue is not too significant and does not require detailed regulations as it is already covered in the law.
Lawyer Nguyen Thanh Ha, Chairman of SBLAW Law Firm, said that previously, most credit institutions and securities companies defaulted to using 360 days to calculate interest rates according to Decision 652/2001 of the State Bank of Vietnam.
Currently, the 365-day calculation method has become the mandatory standard for credit institutions when listing interest rates. Securities companies, on the other hand, usually specify this very clearly in margin loan contracts. According to Mr. Ha, applying both calculation methods is acceptable and does not violate any regulations.
Source: https://tuoitre.vn/diem-mu-lai-suat-margin-chung-khoan-20260517223856731.htm
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