How segments are counted, what your prefix and signature add, and exactly what draws on your allowance — shown before you press send.
SMS is billed by the segment. One segment is 160 characters of plain text; a longer message is split, and each part counts. Add a single character outside the plain set — a curly quote, an emoji, an accented letter — and the whole message switches to Unicode, where a segment holds only 70 characters.
"Evacuate now. Proceed to Assembly Point B." 41 chars 1 segment
The same text with a curly apostrophe in "don't" 41 chars 1 segment (Unicode)
A 200-character plain message 200 chars 2 segmentsThe figure you see is the cost of the message that will actually leave, which is more than the words you typed:
All four are charged, so all four are counted. A prefix is exactly the sort of thing that turns a 158-character message into two segments and doubles the cost of a broadcast, which is why the composer prices it in rather than leaving it as a surprise.
The review step of the campaign wizard shows the whole sum:
1,240 recipients x 2 segments = 2,480 segments,
of which 480 beyond your included allowance.If overage is switched off for your workspace, it says so plainly instead — the send would stop at your included pool rather than continue and bill.
A segment counts once the carrier accepts the message for delivery, in either direction. That means:
Messages stopped before they reach the carrier cost nothing and are not counted: an invalid number, somebody who has opted out, content refused by a screen, or sending suspended.