Free bets: why you keep most of one at long odds and under half at short odds

Concepts2026-10-09

A free bet of 10 backed at 6.0 and laid at 6.2 with 2% commission keeps 7.93 whichever way the event goes, 79.3% of its face value; at 2.0 and 2.1 the same free bet keeps only 47.1%.

• 79.3%kept at 6.0
• 47.1%kept at 2.0
• 95.5%stake returned, 3.0

How Odds Affect Retained Value

The share of value kept from a free bet depends heavily on the odds chosen. As the key figures show, backing at higher odds retains a larger portion of the face value compared to lower odds. This occurs because winnings on a stake-not-returned bet exclude the initial stake amount. At higher prices, the payout relative to the stake is larger, so the excluded stake represents a smaller fraction of the total return. Consequently, the effective loss from the missing stake diminishes as odds rise. The table below illustrates this relationship, showing that the kept share approaches a theoretical limit defined by the odds themselves, minus costs like commission and price gaps.

The Math Behind the Gap

When you lay a bet at an exchange, you cover the liability. For a stake-not-returned free bet, the calculation simplifies because the stake is not part of the return you receive. The formula for the kept share is roughly one minus the inverse of the odds, adjusted for the spread between back and lay prices and exchange commission. At short odds, the inverse of the odds is large, meaning the excluded stake takes a bigger bite out of the total value. At long odds, the inverse is small, so the stake exclusion hurts less. This mechanical difference explains why the kept percentage rises as the price increases, regardless of the specific outcome of the event.

Comparing Stake Returned Bets

A free bet where the stake is returned behaves differently. Here, the full amount comes back regardless of the odds level, provided the bet wins. As the table above indicates, this type of bet retains a significantly higher share of its value even at moderate odds. The comparison shows that a stake-returned bet keeps more value than a stake-not-returned bet at high odds, and far more than one at low odds. The difference arises because the returned stake is not lost to the exclusion rule. Therefore, the efficiency of the bet depends less on the odds level and more on the structure of the return itself.

Practical Implications for Readers

Prices in the market fluctuate, and bookmakers set specific terms for each offer. These variables change the final kept share. You cannot guarantee a specific outcome or profit, as market conditions change and margins apply to every transaction. The goal is to understand how the structure of the bet interacts with the odds chosen. If gambling stops being fun, free help is available. Recognizing that long odds preserve more value in non-returnable bets allows for clearer expectations. Short odds result in a lower retained percentage due to the proportional weight of the excluded stake. This mechanical reality holds true across different scenarios.

Questions

Every figure on this page is computed by code from exact fractions for odds, margins and parlays, and closed-form Kelly growth, each checked by a seeded simulation. See the methodology.