The Core Problem
Betting firms, trainers, and punters all choke on the same thing: how to strip a non-runner from the odds without breaking the math. Look: the moment a horse scratches, the whole pool shifts, and the odds you thought were set become a moving target.
Why the Simple Formula Fails
People love the “total pool minus scratched horse” trick, but it ignores commission, taxes, and the fact that odds are not linear. Here is the deal: you can’t just subtract the non-runner’s stake and call it a day. The deduction must respect the win-bet proportion and the house’s take-out.
Step-One: Isolate the Non-Runner Share
Grab the total amount wagered on the scratched entry. That figure is your starting point. Then, multiply it by the take-out rate — usually 15% for most jurisdictions — to get the net contribution that actually stays in the pool.
Step-Two: Re-calculate the Remaining Pool
Subtract the net contribution from the original pool. Boom. You now have the adjusted pool that will be redistributed among the remaining horses. This is where most calculators go wrong, because they forget the take-out adjustment.
Applying the Adjustment to Odds
Take the new pool total and divide it by each remaining horse’s total stake. That yields the fresh odds. It’s as simple as it sounds, yet the devil is in the decimal places. Round too early and you’ll skew the payout.
Common Pitfalls
First pitfall: ignoring the commission on the non-runner’s stake. Second: failing to update the “each way” terms, which are often tied to the original odds. Third: assuming the non-runner’s odds were a static value — they’re not. They morph the entire market.
Practical Example
Imagine a £10,000 pool, a 15% take-out, and a scratched horse with £2,000 bet. Net contribution = £2,000 × 0.85 = £1,700. Adjusted pool = £10,000 − £1,700 = £8,300. Now, if Horse A had £3,000 on it, its new odds = £8,300 ÷ £3,000 ≈ 2.77 (or 2/1). That’s the real figure you’ll see on the board.
Tools and Resources
Don’t reinvent the wheel. There are calculators online, but you need one that respects the take-out nuance. For a deep dive, check out this guide on calculating non-runner deductions. It breaks down the arithmetic step by step.
Final Actionable Advice
Next time a horse scratches, instantly recalculate the net contribution, adjust the pool, and recompute the odds — no shortcuts, no rounding until the final step. That’s how you keep the market fair and your bankroll safe.