Question: I paid part of my card bill after the due date. Can late charges be calculated on the full bill amount anyway?
Answer: No. Under the RBI credit card directions, late payment charges and related charges can be levied only on the outstanding amount after the due date, not on the total amount due.

Supporting evidence:
title: rbi.org.in/BS_ViewMasDirections.aspx
quote: Late payment charges and other related charges shall be levied, only on the outstanding amount after the due date, and not on the total amount due
context: d-issuers shall report a credit card account as 'past due' to credit information companies (CICs) or levy penal charges, viz. late payment charges and other related charges, if any, only when a credit card account remains 'past due' for more than three days. The number of 'days past due' and late payment charges shall, however, be computed from the payment due date mentioned in the credit card statement, as specified under the regulatory instructions on 'Prudential norms on Income Recognition, Asset Classification and Provisioning pertaining to Advances' amended from time to time. Late payment charges and other related charges shall be levied, only on the outstanding amount after the due date, and not on the total amount due. vi. vi Interest shall be levied only on the outstanding amount, adjusted for payments/refunds/reversed transactions. vii. Changes in charges shall be made only with prospective effect giving prior notice of at least one month.

If a cardholder desires to surrender his/her card on account of any change in charges to his/her disadvantage, he/she shall be permitted to do so without levying any extra charge for such closure, subject to payment of all dues by the cardholder. viii. There shall not be any hidden charges while issuing credit cards free of charge.

DBOD.FSD.BC.No.49/24.01.011/2005-06
November 21, 2005
Credit Card Operations by banks
15.
RPCD.CO.RF.BC.No.2/07.06.00/2005-06
September 17, 2005
Approval for Co-branded Domestic Credit Card Business
16.
DBOD.No.FSC.BC.120/24.01.011/2000-01
May 12, 2001
Credit Card Business of Banks
17.
DBOD.No.FSC.BC.41/24.01.011/2000-01
October 30, 2000
Issue of Credit/Debit Cards by Banks
18.
DBOD.No.FSC.BC.50/24.01.011/1997-98
June 2, 1998
Entry of Banks into Domestic Credit Card Business
19.
DBOD.No.FSC.BC.152/24.01.01/1997-98
December 9, 1997
Domestic Credit Card Business of Banks
20.
DBOD.No.FSC.BC.47/C.469-1990-91
November 7, 1990
Entry of Banks into Domestic Credit Card Business
21.
DBOD.No.BP(FSC).BC.144/C.4691988-89
June 30, 1989
Entry of Banks into Domestic Credit Card Business
(b) List of paragraphs repealed with the issuance of this Master Direction:
No
Paragraph of the Circular/Master Direction
Date
Subject
1.
Paragraph 60 and Annex XVII of the
Master Direction – Reserve Bank of India (Non-Banking Financial Company– Scale Based Regulation) Directions, 2023
October 19, 2023
Issue of Co-branded Credit Cards
(c) All approvals/acknowledgements given under the above circulars shall be deeme