There is no rule regarding the credit amount, but you and your customer should consider their monthly spend, and target that amount, with some cushion. This way, your customer is less likely to need to request credit line increases. Also, keep in mind that your customer will not be declined simply based on the amount they request. For instance, if they apply for $10,000, while they may not be approved for the full amount, they may be approved for a lower amount. Please also refer to the general guidelines for customer key attributes for applying for credit.