Tennis has the strangest scoring system in mainstream sports. Points go 15, 30, 40, then game. A score of 0 is called "love." A tied game at 40-40 is called "deuce," and you have to win two points in a row from there. None of this is intuitive. All of it is centuries old. Here is where each piece comes from.
The clock face theory
The most widely cited explanation for the 15-30-40 sequence is that medieval French tennis (jeu de paume, "game of the palm," played without a racket) used a clock face as a scoreboard. Each point won by a player would move a single hand a quarter turn — 15, 30, 45 — and a fourth point would complete the circle to 60, ending the game.
The theory has some appeal. Quarter-hour increments make intuitive sense as a scoring step. Medieval Europe did use clock-face metaphors extensively for counting. And the original system probably was 15-30-45-60, with 60 being "game."
The change from 45 to 40 happened, in the most likely version of the story, because of how the deuce-and-advantage system was added to the game. Once players needed to win a game by two points, the clock needed to allow for an "advantage" position that did not yet complete the circle. Moving the third score from 45 to 40 left room: 40 → advantage (50) → game (60). The 45–60 spacing left the right amount of room to fit the two-point margin onto the clock.
This is the cleanest explanation, but no one has a definitive primary source for it. The system as we know it was already in place by the time tennis was written about in detail in the 1700s.
Why "love" means zero
The most repeated theory is that "love" comes from the French word "l'œuf," meaning "egg," because a zero on the scoreboard looks like an egg. English speakers adapted "l'œuf" into "love." This is the version most tennis books offer.
The trouble with the theory is that there is no clean evidence trail of "l'œuf" being used to mean "zero" in French tennis records. A competing theory holds that "love" simply means "for love of the game" — i.e., playing for nothing, with no score yet. This is older English usage that predates tennis.
Both theories are plausible. Neither is decisively supported. What is clear is that "love" has meant zero in tennis for at least 200 years, and that no other sport adopted the term, which suggests it is genuinely a tennis-internal convention rather than a generic English usage.
Deuce and advantage
"Deuce" comes from the French "à deux," meaning "at two" — as in, two points are needed to win. Once a game reaches 40-40, you have to win two consecutive points to take it. The first point won goes to "advantage." The second won wins the game. If the player at advantage loses the next point, the score returns to deuce, and the cycle starts over.
The two-point-margin rule is what produces tennis's famously elastic game length. A single deuce game can theoretically go on forever, and the longest recorded games at the professional level have featured 30 or more deuces in a single game.
The modern no-ad debate
Some formats — most notably FAST4, the abbreviated format used in some exhibition and lower-tier events — have removed the deuce-advantage system entirely. At 40-40 in no-ad scoring, a single point decides the game. The receiver typically chooses which side to receive on.
This change is controversial. Defenders of no-ad point out that it makes match length predictable and creates a higher density of decisive points. Detractors point out that it removes one of the most distinctive features of tennis — the long game where momentum swings back and forth. Most major events have kept the traditional deuce-advantage system. Doubles tournaments and team-event formats have been the most willing to experiment.
Why the system stuck
Tennis's scoring system is, by any modern design principle, terrible. It is not intuitive, the names are inconsistent, the math is inelegant, and no one would invent it from scratch today. It has survived because the sport has a continuous tradition stretching back 600+ years, because changing it would require coordination across multiple governing bodies, and because the strangeness is now part of the appeal. Asking someone "why is it 15-30-40 instead of 1-2-3" is one of the first conversations anyone has with the sport — and the answer turns out to involve medieval clocks, French eggs, and a centuries-old compromise about how to handle a tied game.