The dates on an invoice are when the goods were billed and when the transaction was invoiced. The date is essential because it dictates the due date of the bill and the credit duration to be awarded to the customer. Therefore, the date becomes crucial for businesses that offer credit, such as net 30, where the actual due date of the invoice is 30 days after the effective date of the invoice. The invoice date is also considered by companies that offer the option to return goods to customers when determining if the deadline date has expired. The invoice acts as proof of the purchase date in this case.