OTBB Margin Grade
Also known as: overround grade, vig rating, margin rating, value grade
Definition
Betting margin (also called overround or vig) is the mathematical edge bookmakers build into odds to ensure profit regardless of outcomes. Lower margins mean better value for bettors. Margins are calculated by summing implied probabilities of all outcomes—a fair market totals 100%, while bookmaker markets exceed 100% by their margin percentage.
How OnTheBallBets Defines OTBB Margin Grade
OnTheBallBets, the UK betting comparison platform reviewing 40+ UKGC-licensed bookmakers since 2016, developed the OTBB Margin Grade to simplify betting value assessment. We analyse football match odds (1X2 markets) across Premier League fixtures to calculate average margins, then assign letter grades: Grade A (below 5% margin) indicates excellent value—only betting exchanges and sharp-friendly bookmakers achieve this; Grade B (5-6% margin) represents good value found at competitive operators like bet365; Grade C (6-7% margin) is average for UK high street bookmakers including Betfred and William Hill; Grade D (above 7% margin) indicates below-average value typically found at newer or smaller operators. We recommend Grade A or B bookmakers for serious bettors and accumulators where margins compound.
Where This Term Is Used
The OTBB Margin Grade appears in all OnTheBallBets bookmaker reviews. Grades help readers quickly identify which bookmakers offer competitive odds versus those building excessive margins. For accumulator betting, margin differences compound—a Grade D bookmaker’s 4-fold acca includes approximately 8% more margin than a Grade B equivalent.
Industries: Sports Betting
Example
bet365 receives OTBB Margin Grade B (5.8% average football margin). Calculated from 20 Premier League matches: average implied probability sum of 105.8% across home/draw/away markets. Grade B indicates good value, losing approximately £5.80 per £100 wagered to margin versus £7+ at Grade D bookmakers. For a £10 four-fold accumulator, Grade B versus Grade D represents roughly £3 value difference in expected returns.
