How a total is graded
Illustrative example: the total is 145.5. A final of 78–70 is 148 combined points, so the over wins. A final of 72–70 is 142, so the under wins. With a half-point there's no tie.
Pushes
If the total is a whole number, say 145, and exactly 145 points are scored, the bet is a push: your stake comes back and it counts as neither a win nor a loss. That's why 145 and 145.5 are different bets.
Overtime
At most sportsbooks, full-game totals include overtime, and overtime adds points to both teams. Books publish house rules for every market; when in doubt, read them before you bet.
Full-game and second-half totals
Some books also post first-half and second-half totals. A second-half total only counts points scored after halftime (usually including overtime). Those markets post during the break and move quickly; see halftime betting basics.
Price still matters
Overs and unders usually carry juice like any other bet, so the break-even rate applies. Shopping for a better total or price helps the same way it does on spreads.