For example, China Merchants Bank has two credit cards, with a line of 10000 and a line of 20000. Then the total overdraft of the two cards can't exceed 20,000 yuan. Only the card with the highest amount. If the credit card of China Merchants Bank is used, all credit cards (including supplementary cards) under the name of the principal cardholder share the same fixed line, and the credit lines of multiple cards are not accumulated.

Now almost all banks share credit card limits. But bookkeeping and interest calculation are calculated separately. For example, there are two cards, A and B. A spent 5,000 yuan, but B didn't move. The account will show that A and B have reduced the quota by 5,000 yuan at the same time. But to calculate the interest and repayment, you only need to pay back the A card, or you can pay back 2000 yuan. Both AB cards can see that the amount has increased by 2000.

Each card records the consumption amount and calculates the interest separately. For example, the consumption of A is 1000, the interest is 5 yuan, the consumption of B is 2000, and the interest is 15 yuan, which are calculated separately, and there is no need for repeated repayment.

The so-called "shared line" means that all credit cards held by the same cardholder use a common line. Credit cards of the same bank and brand share the same credit limit (usually the highest credit limit of a card). Although several cards have their own credit limits, the total overdraft in use cannot exceed the shared credit limit of the brand credit card.

Source: Baidu Encyclopedia-Sharing quota