Shipment date is an indication of when a package is received at and scanned by your local post office. USPS allows label purchases up to 6 days in advance of package drop off.
When purchasing postage, select the shipment date for when you will drop off the package at your local post office. It is important to keep in mind the Post Office’s hours of operation, as packages submitted to the Post Office after hours (usually 5 pm Monday - Friday and 1 pm on Saturday) should reflect the following day’s date.
While many mail carriers and/or Post Offices will accept packages with a ship date prior to the drop off date, it is USPS’ official policy to deny service to shipments submitted on any date other than that printed on the label. As such, it is always best to drop off your package on the date printed on the label.