Is there any part of Reg. Z that governs how a creditor calculates the available balance on a credit card? I know Reg. Z governs when a payment must be credited, but what if an institution does not want to immediately increase the available balance (up to the limit)? Is this something that is just governed by the account agreement and not any Regulation?

Example: Visa card with $5,000 limit. Outstanding balance is $2,000 with available balance of $3,000. Cardholder makes $700 payment and is credited per Reg. Z. Outstanding balance is adjusted to $1,300 for purposes of calculating finance charge or any other associated charge as dictated by Reg. Z. However, the creditor wants to wait a couple days before adjusting available balance to $3,700.

I couldn't find any Regulatory citation or guidance for this.