Business day is a carrier term. The three big networks do not define it identically, and the gap shows up on Saturdays.
Three carriers, three definitions
Nobody publishes a shared definition, so the practical answer is per carrier. The table below sets the three side by side with the source for each, all read on 2026-07-28.
| Carrier | Saturday delivery | Sunday delivery | How transit is stated |
|---|---|---|---|
| USPS | Ordinary delivery day on the six-day route network | Priority Mail Express only, in many major markets, for an additional fee | Elapsed days, with Sundays and postal holidays excluded |
| UPS | Yes, no fee residential ground, $4 per package commercial ground | No deliveries on Sunday | UPS Ground stated as one to five business days |
| FedEx | Home Delivery reaches 98% of the US population | Home Delivery reaches nearly two thirds of the US population | Business days on express tiers, seven-day operation on Home Delivery |
That third column is the one that catches sellers out. A parcel handed to three carriers on the same Friday afternoon can have three different plausible arrival dates purely from how each one counts.
A Friday drop, worked through
USPS publishes its own examples of the arithmetic, which saves anyone the trouble of inventing a rule.
If you send mail with a 3-day service standard on Friday, the expected delivery date is Monday.usps.com service standards page, checked 2026-07-28
If you send mail with a 3-day service standard on Saturday, the Sunday isn't included and the expected delivery date is Wednesday.usps.com service standards page, checked 2026-07-28
For UPS the equivalent framing is different: ground moves in one to five business days, with the carrier adding that 85% of UPS Ground packages are delivered in three days or less. Saturday delivery exists as a service on top of that count rather than as a day inside it. For FedEx Home Delivery there is no adjustment to make at all, since the network operates through both weekend days.
Five services, one lane, four different windows
This is what the difference looks like on real rates. Every row below was returned in a single SMKlog quote on 2026-07-28 for a 10 x 8 x 4 in box at 1 lb going from Newark, NJ 07102 to Atlanta, GA 30303. Same box, same day, same lane.
| Carrier | Service | Price | Window returned |
|---|---|---|---|
| USPS | Ground Advantage | $9.91 | 8-9 business days |
| UPS | Ground | $10.31 | 2-3 business days |
| UPS | 3 Day Select | $15.13 | 5-6 business days |
| UPS | 2nd Day Air | $16.58 | 2-3 business days |
| FedEx | 2Day | $21.90 | 2-3 business days |
Two things stand out. UPS 3 Day Select quoted 5-6 business days while UPS Ground, $4.82 cheaper on the same lane, quoted 2-3, which happens more often than the service names suggest. And every one of those windows is expressed in business days, so each carrier is applying its own weekend rule to the same physical journey. Read the window that came with your rate; do not translate it from a different carrier.
Business days and weekends: the definitions
Do carriers count Saturday as a transit day?
USPS does, since Saturday is an ordinary delivery day for it and only Sundays and postal holidays drop out of the count. UPS delivers on Saturdays but publishes ground transit as one to five business days. FedEx Home Delivery delivers seven days a week. Read the window that came back with your specific rate rather than assuming a house rule.
How does USPS handle a Saturday send?
It publishes its own worked examples. On the USPS service standards page: if you send mail with a 3-day service standard on Friday, the expected delivery date is Monday, and if you send mail with a 3-day service standard on Saturday, the Sunday isn't included and the expected delivery date is Wednesday (usps.com, checked 2026-07-28).
What does UPS mean by business days on ground?
The UPS domestic services page describes UPS Ground as one to five business days and adds that 85% of UPS Ground packages are delivered in three days or less. Saturday delivery is separately available, free on residential ground and $4 per package on commercial ground unless the account has a scheduled Saturday pickup.
Does a holiday push my delivery date out by a day?
Usually, yes, and by more than a day if the closure sits next to a weekend. Both UPS and FedEx publish dated 2026 calendars showing which days their networks stop, and USPS observes eleven holidays this year. Add each closed day that falls inside your window before you promise a date to a buyer.