No, you may not advertise an APY at three decimal places. Regulation DD requires you to round the APY to two decimal places in advertisements and account disclosures. 

However, Regulation DD includes an exception to this general rule that will permit you to pay interest at the slightly lower rate shown in your account disclosures.  When disclosing the interest rate (but not the APY) in your account disclosures, you may disclose the exact interest rate with more than two decimal places. The Federal Reserve Board explained that this exception was included to “allow the use of the exact contract rate,” acknowledging that the exact interest rate may differ from the disclosed APY.

 For resources related to our guidance, please see:

• Regulation DD, 12 CFR 1030.3(f) (“The annual percentage yield, the annual percentage yield earned, and the interest rate shall be rounded to the nearest one-hundredth of one percentage point (.01%) and expressed to two decimal places. For account disclosures, the interest rate may be expressed to more than two decimal places.”)

• Federal Reserve Board, Final Rule, Truth in Savings, 57 Fed. Reg. 43337, 43347 (September 21, 1992) (“The final rule provides that annual percentage yields are to be shown to two decimal places and rounded to the nearest one-hundredth of one percent (.01%). . . . At the depository institution’s option, however, the interest rate may be shown with greater specificity (more than two decimal places) in account disclosures, in order to allow the use of the exact contract rate.”)