My thought is that it needs to be consistent between both LE and CD.
The piece of regulation that dictates how it should be detailed is 1026.37(m)(4) which states: (4) Late payment. A statement detailing any charge that may be imposed for a late payment, stated as a dollar amount or percentage charge of the late payment amount, and the number of days that a payment must be late to trigger the late payment fee, labeled “Late Payment.”
In the commentary to .37(m)(4) it states – 2. Applicability of State law. Many State laws authorize the calculation of late charges as either a percentage of the delinquent payment amount or a specified dollar amount, and permit the imposition of the lesser or greater of the two calculations. The language provided in the disclosure may reflect the requirements and alternatives allowed under State law.
So based on the regulation you can use dollar amount or percentage and number of days; however, there may be something in your state law dictating otherwise. You will need to check state law to ensure that is not the case.
I do think that regardless of the method utilized it should be consistent between the LE and CD to prevent confusion for the borrower.