Stake-Not-Returned Free Bets: How Much They're Really Worth
A £20 UK free bet isn't worth £20. The retention-rate maths that determines what your sign-up bonus is actually worth, when a "free" bet has negative expected value, and how to extract maximum cash from every promo you take.
A £20 free bet from a UK bookmaker is not worth £20. It is occasionally worth £18, often worth £14, and on a bad day worth £10. The exact figure depends on a piece of arithmetic the bookmakers do not advertise, and the difference between getting it right and getting it wrong is roughly six quid every time you take a sign-up promo. Across a year of promotional churn this compounds into real money.
The phrase "free bet" is doing the work
The "free bet" is the most polite euphemism in British betting marketing. The standard form at UK retail bookmakers is what the industry calls stake-not-returned: the bookmaker hands you a £20 token, you stake it on a market, and if the bet wins, the bookmaker pays out the winnings only. The £20 stake portion is consumed by the token and never returns to you. If the bet loses, you get nothing.
The mechanical version:
- Bookmaker hands you a £20 promotional token
- You stake it on a market priced at decimal X
- On a winning settlement, the bet pays out £20 × X gross
- The bookmaker deducts the £20 stake portion (consumed by the token)
- You receive £20 × (X − 1) in cash. The token is gone either way.
The word "free" is doing significant heavy lifting. The bookmaker is not giving you £20. They are giving you the right to enter one specific kind of bet, on terms they have engineered to suit them. The £20 has approximately zero residual value after the token is created — it cannot be cashed out, it cannot be split across multiple bets at most operators, and it expires in 7-30 days regardless of whether you place a bet.
This is fine. The bookmaker runs a promotion to attract a customer; the customer gets a marginal piece of upside; both sides walk away. The problem is the punter who mentally treats the £20 token as equivalent to a £20 in their wallet. That punter is doing themselves out of money on every promo they ever take.
The retention rate — one formula
There is exactly one piece of maths to learn.
Retention rate = (decimal odds − 1) ÷ decimal odds
This is the proportion of cash-equivalent total return your free bet delivers on a winning settlement. The higher the odds you stake on, the higher the retention.
The table at four price points a UK punter routinely encounters:
| Stake on… | Decimal | Retention | Cash bet win returns | SNR free bet win returns |
|---|---|---|---|---|
| An evens favourite | 2.00 | 50.0% | £40 | £20 |
| A 2/1 horse | 3.00 | 66.7% | £60 | £40 |
| A 4/1 horse | 5.00 | 80.0% | £100 | £80 |
| A 10/1 horse | 11.00 | 90.9% | £220 | £200 |
The retention climbs because the stake-refund "gap" — the £20 the SNR mechanic withholds — becomes a proportionally smaller share of total return as the win returns themselves get bigger.
A worked example: £20 at 3.00 (2/1)
Take a real-shaped UK book. You back the second favourite in a midweek Premier League fixture — Brighton at home, priced 3.00 on the match-result. You stake your £20 sign-up token.
- The bookmaker treats this as £20 placed on Brighton at 3.00
- If Brighton wins, gross settlement = £20 × 3.00 = £60
- Bookmaker deducts the £20 stake portion (consumed by the token): −£20
- You receive £40 cash
Compare to a cash £20 bet at the same price:
- Win: £60 returned (£40 winnings + £20 stake refund)
- Lose: −£20
The cash bet's win returns £60 to your wallet. The SNR free bet's win returns £40. The £20 difference is the stake portion the SNR mechanic withholds — that is the retention gap, costing you a third of the cash-equivalent return.
But the SNR has a redeeming feature the cash bet does not: it costs nothing to place. If Brighton loses, the cash punter is down £20 and the free-bet punter is unaffected. So even though the SNR retains less value on a win, it costs less to enter — which is why even a 50% retention is still better than not taking the offer at all.
Why a longer-priced free bet wins on expected value
The expected value of an SNR free bet at decimal X, on an outcome with true probability p:
EV = p × £20(X − 1)
For a fairly priced bet (where p = 1/X — the bookmaker has the probability right):
EV = (1/X) × £20(X − 1) = £20 × retention rate
Run the numbers at the four price points, assuming each is fairly priced:
- At 2.00 (evens), retention 50%, EV = £10
- At 3.00 (2/1), retention 66.7%, EV = £13.33
- At 5.00 (4/1), retention 80%, EV = £16
- At 11.00 (10/1), retention 90.9%, EV = £18.18
Even on a perfectly fair market the free bet's expected value scales with retention. The £20 token thrown at the favourite is worth £10 in expectation. The same token thrown at a 10/1 longshot is worth £18.18. Same token, same effort, £8.18 better off. The only difference is whether you understood the formula.
Most punters stake their free bet on the favourite. Most punters could not tell you why.
When a "free" bet is actually negative-EV
A free bet that is already credited to your account — no strings attached — can have positive expected value at any odds, because the downside is zero. The token cannot lose you money.
The catch is that almost every UK sign-up offer requires a qualifying bet first. You deposit £20, place a cash bet at minimum decimal 1.50, and only then is the free bet credited. The qualifying bet is your real risk, and it has its own expected value that has to be netted off.
A worked example with reasonable maths:
- Qualifying bet: £20 cash at decimal 1.50, true probability 60%
- EV on the qualifying bet: 0.60 × £10 − 0.40 × £20 = £6 − £8 = −£2
- Free bet: £20 SNR at decimal 5.00, true probability 20% (fairly priced)
- EV on the free bet: 0.20 × £80 = £16
- Combined EV: £16 − £2 = £14 in your favour
Net positive. But the qualifying bet has eaten £2 of value before the free token even hits your account. A different qualifying bet — placed on a worse-priced market, or on a short favourite where the EV is more sharply negative — could eat materially more.
The lesson is short: the cost of a "free" bet is the cost of the qualifying bet plus the retention loss on the token. Both numbers need to clear the value of the offer for the promo to be worth taking. It is genuinely possible to claim a sign-up bonus and net-lose money in expectation. Bookmakers do not advertise that.
Matched betting, in ninety seconds
The pro move is to neutralise the variance on both the qualifying bet and the free bet by laying them off on a betting exchange. The free bet then converts into guaranteed real cash, with the bookmaker's promotional value crystallised before the underlying market settles.
The mechanic on the free bet portion:
- £20 SNR free bet at decimal 6.0 on a horse
- Lay the same horse on Betfair at 6.0 with a backer-money stake of £15
- Lay liability = (6.0 − 1) × £15 = £75
If the horse wins, the free bet returns £100 profit (£20 × 5) and the lay loses £75. Net: £25 cash. If the horse loses, the free bet returns nothing and the lay wins £15 minus 5% exchange commission — £14.25 cash. Both outcomes net positive. The £20 nominal free bet has been converted into £14-25 of guaranteed real money depending on where in the back/lay spread you stake.
This is the whole mechanic of matched betting on sign-up offers. The maths is identical for every UK promo paid in SNR form. The hard part is operational — opening accounts, dodging restrictions ("gubbings"), keeping the discipline — not mathematical.
It builds, of course, on the underlying overround that bookmakers use to price every market in the first place — that piece is the full reference if you want to know why the prices exist before the promos are applied.
Bookmaker rules to read before placing
Every UK retail bookmaker tweaks the SNR mechanic slightly. The common terms to check before you spend the token:
Minimum odds. Most SNR tokens require decimal 1.50 or 1.80 minimum. A token placed at 1.40 doesn't settle.
Single bet vs acca-eligible. Some tokens are single-bet only, some are accumulator-only, some are either. Check before placing — the bookmaker will void the bet if you violate the bet-type rule.
Expiry window. Typically 7-30 days. Sky Bet's promotional tokens often expire in 7. Use them or lose them.
Refund if void. Most books credit the token back if the bet is voided (race called off, match postponed). A small minority don't. Read the T&Cs.
No cash-out. SNR tokens almost always lock the bet. No partial cash-out at 87 minutes when you'd rather take 70% than risk the lot.
Maximum payout. Less common but real. Some operators cap free-bet payouts at £500 or £1,000. Doesn't bite at typical stakes, matters if you've staked the token on a longshot.
Try the maths on your own bet
Before you click "Place Bet" on a real bookmaker slip, plug the numbers into the calculator. Open the main calculator, switch to Free Bet mode, enter the stake, the decimal odds, and toggle "Stake returned" off (the standard UK setting). The retention rate and net cash profit appear instantly, alongside the cash-bet equivalent. You will know within five seconds whether the bookmaker's offer is worth taking and at what odds.
Open the free bet calculator →