12 C.F.R. § 1026.10 – Payments.

(a) General rule. A creditor shall credit a payment to the consumer's account as of the date of receipt, except when a delay in crediting does not result in a finance or other charge or except as provided in paragraph (b) of this section.
(b) Specific requirements for payments—(1) General rule. A creditor may specify reasonable requirements for payments that enable most consumers to make conforming payments.
(2) Examples of reasonable requirements for payments. Reasonable requirements for making payment may include:
1. (i) Requiring that payments be accompanied by the account number or payment stub;
2. (ii) Setting reasonable cut-off times for payments to be received by mail, by electronic means, by telephone, and in person (except as provided in paragraph (b)(3) of this section), provided that such cut-off times shall be no earlier than 5 p.m. on the payment due date at the location specified by the creditor for the receipt of such payments;
3. (iii) Specifying that only checks or money orders should be sent by mail;
4. (iv) Specifying that payment is to be made in U.S. dollars; or
5. (v) Specifying one particular address for receiving payments, such as a post office box.
(3) In-person payments on credit card accounts—(i) General. Notwithstanding § 1026.10(b), payments on a credit card account under an open-end (not home-secured) consumer credit plan made in person at a branch or office of a card issuer that is a financial institution prior to the close of business of that branch or office shall be considered received on the date on which the consumer makes the payment. A card issuer that is a financial institution shall not impose a cut-off time earlier than the close of business for any such payments made in person at any branch or office of the card issuer at which such payments are accepted. Notwithstanding § 1026.10(b)(2)(ii), a card issuer may impose a cut-off time earlier than 5 p.m. for such payments, if the close of business of the branch or office is earlier than 5 p.m.
(ii) Financial institution. For purposes of paragraph (b)(3) of this section, “financial institution” shall mean a bank, savings association, or credit union.
(4) Nonconforming payments—(i) In general. Except as provided in paragraph (b)(4)(ii) of this section, if a creditor specifies, on or with the periodic statement, requirements for the consumer to follow in making payments as permitted under this § 1026.10, but accepts a payment that does not conform to the requirements, the creditor shall credit the payment within five days of receipt.
(ii) Payment methods promoted by creditor. If a creditor promotes a method for making payments, such payments shall be considered conforming payments in accordance with this paragraph (b) and shall be credited to the consumer's account as of the date of receipt, except when a delay in crediting does not result in a finance or other charge.
(c) Adjustment of account. If a creditor fails to credit a payment, as required by paragraphs (a) or (b) of this section, in time to avoid the imposition of finance or other charges, the creditor shall adjust the consumer's account so that the charges imposed are credited to the consumer's account during the next billing cycle.
(d) Crediting of payments when creditor does not receive or accept payments on due date—(1) General. Except as provided in paragraph (d)(2) of this section, if a creditor does not receive or accept payments by mail on the due date for payments, the creditor may generally not treat a payment received the next business day as late for any purpose. For purposes of this paragraph (d), the “next business day” means the next day on which the creditor accepts or receives payments by mail.
(2) Payments accepted or received other than by mail. If a creditor accepts or receives payments made on the due date by a method other than mail, such as electronic or telephone payments, the creditor is not required to treat a payment made by that method on the next business day as timely, even if it does not accept mailed payments on the due date.
(e) Limitations on fees related to method of payment. For credit card accounts under an open-end (not home-secured) consumer credit plan, a creditor may not impose a separate fee to allow consumers to make a payment by any method, such as mail, electronic, or telephone payments, unless such payment method involves an expedited service by a customer service representative of the creditor. For purposes of paragraph (e) of this section, the term “creditor” includes a third party that collects, receives, or processes payments on behalf of a creditor.
(f) Changes by card issuer. If a card issuer makes a material change in the address for receiving payments or procedures for handling payments, and such change causes a material delay in the crediting of a payment to the consumer's account during the 60-day period following the date on which such change took effect, the card issuer may not impose any late fee or finance charge for a late payment on the credit card account during the 60-day period following the date on which the change took effect.