Add-on cards - Effect on Credit score: As supplementary credit cards are connected to the primary card, all the transactions and bill payments regarding the cards will be recorded similar to that of primary credit cards.If the primary cardholder is unable to clear the due or pays only the minimum amount due repeatedly, he/she runs the risk of racking up a debt.If payments are delayed, late charges will be deducted from the account of the primary cardholder. Any defaults on the account will also be reported to credit agencies like CIBIL and Experian.Therefore, primary cardholders need to be very careful about the supplementary cardholder's spends because if anything goes wrong, it will reflect on the primary cardholder's account and might affect the credit score.