An add-on card is a supplementary card taken on a primary card. As the add-on card is connected to the primary card, the repayment behaviour of the add-on card reflects on the primary card’s credit score. This means if the bill of the add-on card is not paid timely or if only minimum due payments are being made, then the credit score of the primary cardholder is bound to deteriorate.

So, ensure you make full payments and pay your bills on time so as to keep a decent credit score. Additionally, it is recommended that you try to keep you credit utilisation, or the proportion of credit used vis-à-vis the credit limit available, in control.