# BUS/252 accrual - why 252?

I've recently found out about the BUS/252 accrual method used in Brazil, where, to calculate how much of the yearly accrual falls on a given period by calculating the number of business days during that period and then dividing by 252.

Assuming a week has 5 business days we get at least 260, at most 262 business days during a calendar year. What is the reason for 252 being used - is average number of weekday bank holidays in Brazil during calendar year 9? Is there any place online where I can read more on what exactly is considered "business days" for this accrual method?

Business days are all weekdays excluding holidays under the respective settlement calendar. The "252 business days per year" rule of thumb is quite common not only in Brazil - see e.g. here. The reason is, as you suspected, that the average number of business days over a year are often around 252.

The rationale for 252 business days is the following:

• 30 days / month;
• 2 non business days / week;
• 4.5 weeks / month, on average;
• 2 * 4.5 = 9 non business days / month;
• 30 - 9 = 21 business days / month;
• 21 * 12 months = 252 business days / year
• this is a kind of weird way to calculate it, and it feels like you've done it this way just to end up with 252. The more sensible way is to say that there are 52 weeks per year. 52*5 = 260. And then subtracting from that the average number of trading holidays.
– will
Commented Feb 10, 2019 at 11:40