For schema BankingAccountDetail, there are instances where multiple current
lendingRate values apply on a consumer's account. This occurs PER_TIER deposit rates where the customer is receiving different interest rates on their tiered balances. It may also occur for different credit card lending rates for the customer's purchase balance vs balance transfer portion of balance.
How do we represent this?
If the customer has $25,000 in their account and is receiving 0.2% on the first $15,000 and 0.5% on the next $10,000, what do we put for the additional depositRate field? Do we calculate the effective interest rate as (0.2% x 15,000)+(0.5% x 10,000) = 0.32% and recalculate on a daily basis?
The BankingAccountDetail schema supports the full complexity available in Product Reference Data (PRD). It also includes an additional field that is supposed to indicate the current interest rate for this specific account at the time of the API call. This could be considered the 'effective' rate.
Currently, you would do the calculation as you suggest and then provide that. The alternative is that every Accredited Data Recipient has to implement the onerous calculation you describe, in order to show the customer their current effective rate. As with much of the standards, the choices balance implementation costs and use, across all participants.
You can, of course, raise a change request in the Consumer Data Right Standards Maintenance GitHub repository.