Betfair Lay Stake Calculator with Commission: Formula and Examples

A lay stake calculator answers one practical question: how much should you lay on Betfair so the profit is the same whichever outcome wins? The calculation changes when exchange commission applies. Ignoring even a small commission can leave an uneven hedge.

This guide explains the formula for a back-to-lay hedge, shows examples, and covers what changes when you are using a free bet or a betting exchange with a different commission rate.

A back bet wins when your selection wins. A lay bet takes the opposing side: you win the lay stake when the selection loses and pay the liability when it wins.

Use these values: back stake B, back odds O, lay odds L, and commission C expressed as a decimal. For example, 5% commission is 0.05. Commission is normally charged only on the exchange profit of the winning market.

For a standard qualifying or hedged back bet, calculate the lay stake as:

Lay stake = (Back stake × Back odds) / (Lay odds − commission)

The denominator is not simply the lay odds. It is lay odds minus the commission rate. That adjustment equalizes the two possible outcomes.

Suppose you backed a team for $20 at decimal odds of 3.00. Betfair now offers lay odds of 3.20 and your commission rate is 5%.

Lay stake = (20 × 3.00) / (3.20 − 0.05) = 60 / 3.15 = $19.05.

Your liability is lay stake × (lay odds − 1), so $19.05 × 2.20 = $41.91. Enter $19.05 as the lay stake, then confirm the exchange displays the expected liability before submitting.

If the selection wins, the back bet returns $60 including stake and you lose $41.91 liability on the exchange. If it loses, you lose the $20 back stake and win roughly $18.10 after 5% commission on the $19.05 exchange profit.

The exact figures can differ by a cent because exchanges round stake, liability, or commission. The goal is not perfect theoretical precision; it is to ensure the residual imbalance is small and understood.

Liability is the amount at risk on the exchange if the selection wins:

Liability = Lay stake × (Lay odds − 1)

New exchange users often confuse stake and liability. When you lay $20 at odds of 5.00, you are risking $80, not $20. Keep enough cleared balance in your exchange wallet before committing a hedge.

A stake-not-returned free bet has a different formula because you do not receive the free-bet stake as part of the return. Do not use the standard qualifying-bet formula for it.

Before calculating, identify whether the promotion returns the stake, whether the free bet can be split, and whether it applies to exchange lay markets. Terms determine the math more than the headline bonus amount.

The most common errors are entering commission as 5 instead of 0.05, using back odds where lay odds belong, forgetting to check liability, and calculating from odds that have already moved. Another mistake is hedging a market with different settlement rules, such as regular time on one side and extra time included on the other.

Always compare the event, market name, participant, and settlement conditions before placing both sides.

A calculator saves time, but it cannot verify market compatibility or available liquidity. Treat it as an arithmetic tool, not a risk-control system. Check that the exchange accepts your calculated stake at the displayed odds and that the matched amount is complete.

For a broader execution checklist, read our guide to verifying a ready arbitrage trade before placing.

Confirm the back stake and odds, enter your actual commission rate, calculate the lay stake and liability, check matched liquidity, and verify settlement rules. If the odds move, calculate again. A correct lay stake is useful only when it matches the live market you can actually place.