▌ Calculator · bonus bet · updated 2026-05-09
Free bet.
Real cash.
No risk.
A $50 sportsbook bonus doesn't have to be a gamble. Back a selection with the free bet, lay it off on an exchange, and both outcomes pay roughly the same — around $38–$42 in cash regardless of which side wins. The exact amount depends on which odds you pick and your exchange's commission rate.
This calculator solves the matched betting equation for standard stake-not-returned (SNR) free bets. Enter the bonus value, back odds, lay odds, and commission. It returns the exact lay stake to place, the liability to set aside, and your guaranteed profit under both outcomes.
Calculator
Live · client-side · zero tracking▌ Free / bonus bet details
Betfair standard: 5%. Smarkets: 2%.
▌ Free bet conversion
Guaranteed profit
+$31.67
63.3% return on $50.00 bonus bet
Lay stake
$33.33
Place on exchange
Lay liability
$68.33
Funds to lock
If back wins
+31.67
If back loses
+31.67
Free bet stake not returned on win — only profit is paid.
Formula: lay stake = free bet × (back − 1) ÷ (lay − commission)
▌ Derivation · matched betting formula
The lay stake formula
Let F = free bet amount,
b = back decimal odds,
l = lay decimal odds,
c = commission rate (e.g. 0.05 for 5%).
Because the free bet stake is not returned on a win (SNR), the back profit equals
F × (b − 1). The lay profit when the back bet
loses is L × (1 − c) (where L is the lay stake),
since the lay wins the lay stake minus commission. Setting these equal:
F × (b − 1) = L × (l − 1) [win case]
L × (1 − c) = profit [lose case]
L = F × (b − 1) / (l − c)
This is the matched betting lay stake formula for SNR bonuses. The denominator uses
l − c (lay odds minus commission) rather than
l − 1 because the lay profit on a losing back bet
is the lay stake less the commission, not the gross lay stake.
Worked example
$50 free bet, back odds +200 (3.00 decimal), lay 3.05, Betfair 5% commission:
L = 50 × (3.00 − 1) / (3.05 − 0.05)
L = 50 × 2.00 / 3.00
L = $33.33
Lay liability = 33.33 × (3.05 − 1) = $68.33 (funds to reserve)
If back wins: $100 profit − $68.33 lay loss × commission ≈ +$36.67
If back loses: $33.33 × 0.95 commission = +$31.67
Conversion rate = average profit / free bet = ~$34 / $50 = 68%. At higher back odds
(e.g. +300), conversion climbs toward 80–85% because the numerator
(b − 1) grows faster than the denominator adjusts.
Use the calculator to scan odds before placing.
For pure arbitrage (real money, not a free bet) across two sportsbooks, use the arbitrage calculator instead. For hedging an existing open bet, use the hedge calculator.
▌ Reference
Free bet conversion at a glance
Based on a $100 SNR free bet, 5% Betfair commission, lay odds ≈ back odds + 0.05.
| Back odds | Lay odds | Lay stake | Approx. profit | Conversion |
|---|---|---|---|---|
| +150 (2.50) | 2.55 | $66.67 | ~$63 | ~63% |
| +200 (3.00) | 3.05 | $66.67 | ~$73 | ~73% |
| +250 (3.50) | 3.55 | $71.43 | ~$78 | ~78% |
| +300 (4.00) | 4.05 | $75.00 | ~$81 | ~81% |
| +400 (5.00) | 5.05 | $80.00 | ~$85 | ~85% |
| +500 (6.00) | 6.05 | $83.33 | ~$87 | ~87% |
▌ FAQ
Common questions
What is a bonus bet (free bet) and how does matched betting work?
How is the lay stake calculated for a bonus bet?
What is the difference between SNR and SB (stake back) free bets?
What odds should I use to maximize free bet conversion?
Which exchange commission rate should I use?
Can I use this calculator for cash matched betting (not free bets)?
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