Free tool
Totals Line Value Calculator
Enter your own estimate of how a match's total games are distributed: this tool does the probability math for any line, so you can check several books' totals lines against the same estimate at once.
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How this is calculated, and what it deliberately doesn't do
This treats total games as roughly normally distributed around your mean and standard deviation, then reads off the probability of landing over or under any line from the normal distribution. It's a standard, honest approximation, nothing more.
What it does not do: predict the mean or spread for you. We tested a model that generates those numbers automatically from serve stats, and found it systematically overestimated match length by several games. See the note on our methodology page about why that model stays disabled until it's properly recalibrated. This tool only does the math on numbers you provide, the same honest boundary as the other calculators here.
A reasonable starting point for a competitive best-of-three match between similarly matched players is a mean in the low-to-mid 20s with a standard deviation around 3-4 games, but treat that as a rough anchor to adjust from, not a prediction.
Worked example: mean 22.5 games, spread 3.5, line 21.5
- The line sits 1 game below your mean, which is 1 ÷ 3.5 = 0.29 standard deviations.
- From the normal distribution: P(Over 21.5) = 61.2 %, P(Under) = 38.8 %.
- Fair odds: Over 1.63, Under 2.58.
- A book offering Over 21.5 at 1.80 would be above your fair 1.63; at 1.55 it would be below it.
Common mistakes
- Guessing the mean from the line. The line is the bookmaker’s opinion; your mean has to come from somewhere else.
- Using one spread for every match. Mismatches end quickly and vary less; close matches with tiebreaks vary more.
- Forgetting best of five. Grand Slam men’s matches have a completely different total.
In tennis
Total games depend on serve strength and how even the match is. Two big servers produce tiebreaks and higher totals; a clear favourite produces short matches. We tested an automatic serve-based model for this and keep it disabled because it overestimated match length.
Read next: How often matches end in straight sets · No-vig calculator · Methodology
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