Short Answer:

You should avoid new purchases on a balance transfer card because many cards apply the 0% APR only to transferred balances. New purchases may accrue interest immediately, which can increase your overall debt even during the promotional period.

Adding new charges can make it harder to pay off the transferred balance before the promotion ends and may reduce the savings from the 0% APR offer. Focusing on repaying the transferred balance first ensures maximum financial benefit and better debt management.

Detailed Explanation:

Interest Rules on New Purchases

Balance transfer cards often offer a 0% APR on transferred balances for a set period, such as 6–18 months. However, new purchases made on the card may not be included in the promotional rate. Instead, they may accrue interest immediately at the standard APR. This means that while your transferred balance benefits from interest-free repayment, any new purchases could start generating charges right away.

Impact on Debt Repayment
Making new purchases can increase the total balance owed on the card, making it harder to pay off the transferred balance within the promotional period. Since interest is charged on new purchases immediately, your overall payments may be higher than planned. This can reduce the savings you expected from the 0% APR offer and extend the time it takes to become debt-free.

Credit Utilization Considerations
Adding new purchases also increases your credit utilization ratio, which is the proportion of your available credit that you are using. A higher utilization ratio can negatively affect your credit score. Keeping new purchases to a minimum helps maintain lower utilization, supporting both financial health and credit score improvement.

Financial Planning Strategy
To maximize the benefits of a balance transfer card, focus solely on paying down the transferred balance first. Avoid making new purchases until the transferred balance is fully repaid. This ensures all payments go toward reducing the principal and taking full advantage of the 0% APR period. Using automatic payments, setting reminders, and creating a monthly repayment plan can help maintain discipline.

Risks of Ignoring This Advice
If new purchases are added, interest charges can accumulate unexpectedly. In some cases, this may trigger higher APRs if payments are missed or balances grow too large. The combination of interest on new purchases and the transferred balance can quickly undermine the financial advantage of using a balance transfer card.

Conclusion

Avoiding new purchases on a balance transfer card is essential to maximize the benefits of the 0% APR promotional period. New charges can accrue interest immediately, increase debt, and make it harder to pay off the transferred balance. Focusing on repaying the transferred balance first ensures savings, effective debt reduction, and better financial control.