First-Class Mail services have an estimated delivery time of 1-5 business days—day-definite delivery is not available with this service. Tracking is not available for First-Class Mail shipments, though delivery confirmation services such as Certified Mail may be available.

In 2026, following the USPS restructuring, the service formerly known as "First-Class Package Service" has been largely integrated into USPS Ground Advantage. For standard lightweight packages (under 15.99 oz), the expected delivery time is typically 2 to 5 business days across the continental United States. While not as fast as "Priority Mail" (which is 1 to 3 days), Ground Advantage is the most cost-effective "trackable" service for small e-commerce shipments. Delivery speed is heavily influenced by the distance between the "Zone" of origin and the destination; a package moving within the same state might arrive in 48 hours, while a cross-country shipment from New York to California will likely take the full 5 days. It is important to note that this service is not "guaranteed," meaning the delivery date is an estimate rather than a contract. For those who need absolute speed, Priority Mail Express remains the only domestic service that offers a 1-day or 2-day money-back guarantee regardless of the season.