If you bet on horse racing regularly, you probably compare odds between bookies to squeeze out every bit of value you can. But there’s a lesser-known concept that can massively influence your returns — overround. It’s how bookmakers build in their margin on a race, and understanding it helps punters identify when odds are fair… and when the bookie edge is stacked against you.

If you’re comparing racing odds and want to see which firms consistently offer value, our breakdown of the top 20 UK betting sites is a great place to start.

In this guide, we explain what overround means, why it matters in horse racing, how to calculate it, and how you can use it to your advantage.

The 'Overround' is the percentage above 100% that represents the bookmaker's built-in profit margin on a market.

In a totally fair market, the total implied probabilities of all runners would equal 100%. But bookies add a margin to ensure they make money no matter who wins - and that extra percentage is the overround.

Understanding the overround is paramount to extracting the most value from your bets - and it differs greatly in horse racing compared to other popular markets like football.

Horse racing has loads of runners relative to most sports. A Premier League match only has three possible outcomes (home/draw/away) — but a racing field can have 5, 8, 12, or sometimes in excess of 20 horses.

More runners = more overround = more bookmaker margin baked into odds.

Understanding overround helps you:

• 🎯 Identify fairer odds and value betting opportunities
• 📉 Spot when a market is overpriced and avoid it
• 💻 Choose bookmakers that consistently offer better racing margins
• 📊 Improve long-term ROI instead of falling victim to the house edge

For serious racing punters, this knowledge is gold.

As a rule of thumb, the closer the number is to 100%, the better. Any sports betting market with an overround of above 115% is probably not worth it.

You're more likely to find lower overrounds in big events, such as Royal Ascot and Cheltenham due to higher competition amongst bookies.

❌ High Overround (115%) = Not great value

✅ Low Overround (102%) = Excellent value

Key Points

• Horse Racing major events such as Cheltenham and Grand National usually result on low overrounds.
• Betting Exchange sites usually offer better value
• Overround usually starts dropping in the build-up to the race with markets beginning to settle

You've now got an understanding of how overround works in horse racing - now it's time to put it into practice.

If you've got an eye on an upcoming horse racing event like Cheltenham, Royal Ascot or the Grand National then it's the perfect time to check out the best betting sites offering new welcome bonuses.

Bookies often inflate their sign-up offers to entice new customers - meaning more free bets for the punters!

Below we've handpicked our top three horse racing betting sites for you to check out!