In WTA tennis, spread betting — commonly referred to as game spreads or handicaps — involves giving one player a head start or deficit in total games across a match. For the Charleston Open, a spread of -4.5 on a favorite means she must win by at least five more games than her opponent across all sets. This differs from team sports like football or basketball where point spreads apply to a single final score; in tennis, the spread captures the margin of dominance across the entire match structure, making set-by-set dynamics and tiebreak scenarios critical variables.
The spreads market at Charleston is particularly valuable when there's a significant skill gap on green clay, a surface that can amplify stylistic mismatches — heavy topspin players tend to dominate on this slower surface, often producing lopsided scorelines. Bettors should monitor first-round matchups where top seeds face qualifiers, as these frequently produce wide game margins. It's also worth noting that vig on WTA spreads tends to run slightly higher than on moneylines or match totals, since books face more uncertainty pricing exact margins. Comparing vig across sportsbooks for Charleston spreads can yield meaningful savings, especially on lines where books disagree on a player's clay-court form.
Analysis updated September 27, 2026. Odds data above refreshes hourly.
Spreads Vig Rankings
| # | Sportsbook | Vig | Grade | Events |
|---|---|---|---|---|
| 1 | LowVig.ag | 4.62% | B | 1 |
| 2 | BetOnline.ag | 4.62% | B | 1 |
| 3 | BetRivers | 5.97% | C+ | 1 |
| 4 | betPARX | 5.97% | C+ | 1 |
| 5 | Bally Bet | 5.97% | C+ | 1 |
| 6 | Bovada | 6.78% | C | 1 |
| 7 | BetUS | 6.78% | C | 1 |
| 8 | BetAnything | 6.93% | C | 1 |
Frequently Asked Questions
What is a point spread bet?
A point spread bet levels the playing field by giving the underdog a head start. If the spread is Patriots -7, they must win by more than 7 points for a spread bet to pay. Spreads are the most popular market in football and basketball, which means they attract the most volume and typically have the lowest vig.
Why do spreads usually have lower vig than moneylines?
Spreads attract the highest betting volume because they create a roughly 50/50 proposition regardless of team quality. This balanced action means sportsbooks don't need wide margins to manage risk, resulting in tighter vig — often the best value available.
What is vig (vigorish) in sports betting?
Vig — short for vigorish, also called juice or overround — is the margin a sportsbook builds into its odds. It's the difference between the true probability of an outcome and what the odds imply. Lower vig means you keep more of your winnings on every bet. For example, a standard -110/-110 line has about 4.76% vig.
How often is this data updated?
We pull fresh odds from The Odds API every hour, on the hour (UTC). Each snapshot captures the latest lines from every sportsbook that has posted odds. The timestamp at the top of the page shows the most recent refresh.
How is the vig grade calculated?
Each sportsbook is graded on average vig: A+ (under 2%) is exchange-level pricing, A (2–3%) very competitive, B+ (3–4%) above average, B (4–5%) the industry standard, C+ (5–6%) slightly below average, C (6–7%) below average, D (7–8%) high vig, D− (8–10%) very high, F (10%+) predatory.
Why does lower vig matter for bettors?
Lower vig directly impacts your long-term returns. A bettor placing $1,000 per week at a book with 4% vig loses roughly $40/week to the house edge. At 2% vig, that drops to $20/week — a $1,040 difference over a year. For serious bettors, shopping for lower vig is one of the most reliable ways to improve profitability.
What sportsbooks do you track?
We track both regulated US sportsbooks (DraftKings, FanDuel, BetMGM, Caesars) and offshore books (Bovada, BetOnline, MyBookie, BetUS, LowVig.ag, BetAnything). Data comes from The Odds API, which aggregates real-time lines from licensed sources.
How We Calculate These Numbers
- Data Source
- All odds on this page come from The Odds API, which aggregates real-time lines from licensed US and offshore sportsbooks. We track moneyline, spread, and totals markets across every sport with active betting lines.
- Update Frequency
- We pull a fresh snapshot of every tracked market every hour, on the hour (UTC). Each snapshot captures the latest lines from every sportsbook that has posted odds for a given event. The timestamp at the top of each page tells you exactly when the data was last refreshed.
- Vig Calculation
- Vig (short for vigorish, also called juice or overround) measures the margin a sportsbook builds into its odds. We calculate it by converting the odds on each side of a market to implied probabilities, summing those probabilities, and subtracting 100%. For example, a market priced at -110/-110 implies 52.38% on each side — a total of 104.76%, meaning a vig of 4.76%. Lower vig means better value for bettors because you keep more of your winnings.
- Per-Market Breakdown
- We compute vig separately for each market type: moneyline (h2h), point spreads, and totals (over/under). The "average vig" shown for each sportsbook is the mean across all market types weighted by the number of events sampled in each market.
- Grading Scale
- Every sportsbook receives a letter grade based on its average vig: A+ (under 2%) is exchange-level pricing. A (2–3%) is very competitive. B+ (3–4%) is above average. B (4–5%) is the industry standard — a -110/-110 line is 4.76%. C+ (5–6%) is slightly below average. C (6–7%) is below average. D (7–8%) is high vig. D− (8–10%) is very high vig. F (10%+) is predatory pricing. See the full Vig Index Methodology for formulas, worked examples, and known limitations.
- Trend Tracking
- We store daily snapshots for 30 days, allowing us to show 24-hour and 7-day vig trends. A downward trend (improving) means sportsbooks are tightening their lines — often in response to increased competition or higher betting volume as a season heats up.