A dedicated movement, not a network
Ordinary parcel service works because thousands of packages share the same trucks and sorts. Same-day breaks that: the shipment gets a specific vehicle or a specific seat on a flight, and you pay for that capacity rather than for a share of it. Every quote therefore depends on the exact pair of addresses, the hour, and what else is moving nearby.
The carrier version exists and is priced on request
FedEx publishes two same-day services, one for envelopes and packages up to 150 lbs and one for palletized freight or multiple packages of 151 lbs or more. Coverage is described as door-to-door delivery throughout all 50 states, 24 hours a day, 7 days a week, 365 days a year, including holidays, with prior approval required if any single package exceeds 70 lb or has dimensions over 48 inches. Booking is through a dedicated site with an account or by phone, and no prices appear on that page. All quoted from fedex.com, checked 2026-07-28.
Retail same-day is a different animal
Most people meeting the phrase are seeing a shop's own local delivery, fulfilled from a nearby store by a courier platform. That is a retail service tied to that shop's stock, not a shipping product you can buy for your own parcel, and it is worth separating the two before comparing prices.