I have a question regarding the day count conventions for T-bills, T-notes and T-bonds. So far I haven't found an official page that clearly states which method is used and I don't own bloomberg etc. to look it up myself. I have also looked at the TreasuryDirect website but it is not there either. However, Investopedia states that:
Actual/360 is most commonly used when calculating the accrued interest for commercial paper, T-bills . . . Actual/365 is most commonly used when pricing U.S. government Treasury bonds...
Can someone tell me if this is correct and why the term "commonly" is used, i.e. are there T-bills/T-bonds that have other day count conventions? Also who defines which method is used. The U.S. Treasury ?
Thans in advance.