Many couples adopt an "AA" system of living after marriage, agreeing that their income belongs to themselves individually and that daily expenses are shared equally. It is generally believed that debts can also be independently incurred and not interconnected. However, at the legal level, the "AA" system for couples cannot completely exempt them from joint liability for debts. Whether debts need to be jointly undertaken depends on the form of the agreement, the purpose of the debt, and the awareness of the creditor, and it is not as simple as each person bearing their own share.

  According to Article 1065 of the Civil Code, husband and wife may agree in writing that the property during marriage shall be owned separately, and such agreement shall have legal effect internally and can clearly define the distribution of property and liabilities between the two parties. However, there are restrictions on the agreement externally, and it can only counteract third parties when the creditors are clearly aware of the content of the agreement; if the creditors are unaware, the internal AA system agreement cannot bind the creditors, and the debt may still be identified as joint debt of the husband and wife.

In judicial practice, the standard for identifying joint liabilities of married couples strictly applies Article 1064 of the Civil Code. First, liabilities with joint intention, debts jointly signed by both parties and subsequently recognized, regardless of whether the AA system is implemented, are considered joint liabilities; second, daily household liabilities, debts incurred by one party within a reasonable range for the family's clothing, food, housing, transportation, medical care, and education, are presumed to be joint liabilities by law; third, large-scale purpose liabilities, where a large single-party loan is actually used for the joint life and joint business of the couple, are also considered joint liabilities.

  It should be noted that oral agreements for mutual payment arrangements have weak evidence, and courts generally do not accept them. Even if there is a written agreement, the legal debts arising from the custody of children and the support of the elderly still need to be jointly undertaken by both parties and cannot be exempted through internal agreements. If a single party's debt is obviously beyond the scope of the family's daily life and is not used for joint living, it does not constitute the joint debt of the couple.

In summary, the husband and wife cost-sharing system only divides rights and responsibilities internally and cannot absolutely isolate external debts. It is recommended that couples who implement the cost-sharing system must sign a written property agreement and keep relevant documents; when borrowing individually, they should actively inform the creditor of the property agreement to avoid unilateral borrowing being mixed with household expenses, prevent unnecessary “being burdened with debt” risks, and balance the rights and interests of both spouses and transaction safety.