us post office next day rates are the costs associated with sending a package via USPS’s Priority Mail Express service, which guarantees next-day delivery. USPS offers competitive rates for this service, with pricing based on the size, weight, and destination of the package. Priority Mail Express includes tracking, delivery updates, and insurance for packages valued up to $100. For smaller, lighter packages, USPS provides a more affordable alternative to overnight shipping with its flat-rate envelopes and boxes, which are priced based on the service rather than weight.