Sure Bets 100 Percent: Maths-Based Locks vs 'Sure Win' Tips

By the AUOdds team · Updated 15 Oct 2026 · 7 min read

Sure bets 100 percent is a phrase used for two very different things, and only one of them deserves the name. Search for it and you'll find plenty of tipster predictions labelled as sure bets. A genuine sure bet is something else. It is an arbitrage position where you back every outcome of an event at different licensed bookmakers, with stakes sized so the result doesn't matter. This guide separates maths from tips and explains what the term really means. It walks through one worked Australian lock with real-looking prices. It also covers the risks that remain, from moving prices to voided bets and limited stakes. There are no predictions here, just how it works.

What does 'sure bets 100 percent' actually mean?

A search for sure bets 100 percent turns up two very different things. One is a tipster's prediction with a confident label attached. The other is a maths-based position, usually called arbitrage. You back every possible outcome at different bookmakers, and the combined odds lock in a return at the prices shown.

Only the second matches the original sure bets meaning. The term comes from arbitrage. When bookmakers disagree enough on a price, the total of their implied probabilities drops below 100%. That gap is what you capture. It has nothing to do with predicting who wins.

In plain terms:

• A real sure bet covers every outcome of an event, with stakes sized so each result returns roughly the same amount.
• A tip picks one outcome and hopes it lands. However confident the tipster, a single-outcome bet can lose.

The '100 percent' refers to coverage, not certainty. You have covered 100% of the outcomes in the market. Whether the return actually arrives still depends on three things:

• prices holding while you place both bets
• the bookmaker accepting your full stake
• both bets settling as expected

Those are real risks, and we cover them below.

It's worth separating the two ideas early. Many sites use 'sure bet' to mean 'a pick we feel strongly about'. That's a marketing use of the phrase, not the betting one.

Why aren't 'sure bets sure win' tips real sure bets?

Pages promising sure bets sure win results are almost always selling predictions. They might analyse form, injuries and head-to-head records, and some of that analysis may be thoughtful. But in the end you are asked to back one side. If that side loses, your stake is gone.

Here's a quick way to recognise the difference:

• Number of bets. A tip is one bet. A lock is two or more bets, one on each outcome, usually at different bookmakers.
• What decides the result. A tip depends on the game. A lock depends on the prices, and the game result only decides which of your bets pays.
• What you can check. You can't verify a tipster's confidence before the start. You can verify a lock yourself in seconds by adding up one divided by each price.
• How the return is described. A lock locks in a return at the prices shown. A tip offers a possible win and a possible loss.

There's also a pricing reality. Bookmakers build a margin into every market. If you back one tip after another, that margin works against you over time, even when the picks feel strong.

A lock only works because two bookmakers have priced the same event differently. For a moment, the gap is big enough that the combined margin falls below zero.

None of this means every tipster is dishonest. It means the label is wrong. If someone calls a single-outcome pick a '100% sure bet', treat it as a prediction and judge it like one.

Sure bet explained: how does the maths work?

Here is the sure bet explained in one step. Convert each decimal price to an implied probability by dividing 1 by the odds. A price of 2.00 is 50%. A price of 1.80 is about 55.6%.

Within a single bookmaker, the implied probabilities across all outcomes add up to more than 100%. The extra is the bookmaker's margin. For example, a two-way market priced at 1.90 and 1.90 adds up to about 105.3%.

A lock appears when you take the best price for each outcome from different bookmakers and the total comes in under 100%. Say the best prices are 2.08 and 1.99. The total is about 98.3%. The gap, roughly 1.7%, is your locked return on the total outlay at those prices.

To size each stake so every result pays the same:

• Pick a total outlay, say $500.
• For each outcome, divide its implied probability by the total implied probability.
• Multiply that share by your total outlay.

Two practical points matter.

First, every outcome must be covered, including a draw where the market has one. Missing an outcome turns a lock into an ordinary bet.

Second, the gaps are small. AUOdds data shows 1,890 locks over the last 30 days, with a typical lock of about 1.8%. That's a thin edge, which is why accuracy and speed matter more than opinion.

What does a real Australian lock look like?

Here's a short worked example using two licensed Australian bookmakers on a pre-match tennis market. The prices are illustrative.

• Bookmaker A: Player 1 at 2.08
• Bookmaker B: Player 2 at 1.99

First, the implied probabilities:

• 1 ÷ 2.08 = 0.4808
• 1 ÷ 1.99 = 0.5025

Together that's 0.9833, or about 98.3%. That's under 100%, so the prices lock.

With a $500 total outlay:

• Stake on Player 1: 500 × 0.4808 ÷ 0.9833 = about $244.50
• Stake on Player 2: 500 × 0.5025 ÷ 0.9833 = about $255.50

The returns:

• If Player 1 wins: $244.50 × 2.08 = $508.56
• If Player 2 wins: $255.50 × 1.99 = $508.45

Either way you get back about $508.50 on $500 staked. That's a locked return of roughly $8.45 to $8.56, or about 1.7%, at the prices shown.

Notice what didn't matter: who you thought would win. The whole return came from the gap between two bookmakers' prices.

Also notice how small it is. Suppose Player 2's price shortens from 1.99 to 1.95 before you place the second bet. That side would then return about $498, a small loss if Player 2 wins.

A stake typo can do the same. That's why the checks in the next section matter.

What can still go wrong with a sure bet?

A lock removes the need to predict, but it doesn't remove every risk. These are the ones that catch people out.

Prices move. Odds change constantly. Across about 15,000 tracked prices at 9 bookmakers, even data around 10 seconds old can shift between seeing a price and placing your bets. Place the harder-to-get side first, then recheck the other price before placing the second bet.

Stakes get limited. A bookmaker may accept only part of your stake, or limit your account over time. If one side is cut short, your stakes no longer balance and one outcome can lose money. Don't assume full acceptance.

Bets can be voided. Each bookmaker sets its own settlement rules, and they don't always match. A tennis retirement, a postponed match or an obvious price error can see one bet voided or settled differently from the other. Read each bookmaker's rules for the market before you bet.

Mistakes happen. Any of these can turn a lock into a loss:

• backing the wrong player
• choosing the wrong market, such as a handicap instead of the match result
• typing $25.55 instead of $255.50

Slow down and double-check each bet slip.

Timing. Online in-play sports betting isn't offered to Australians, so the locks you can place online here are pre-match. Prices often move as an event approaches, which makes speed and care equally important.

None of these risks is rare enough to ignore. Plan for them rather than hoping they won't happen.

How do you sure bet sensibly in Australia?

If you're working out how to sure bet properly, a simple routine beats enthusiasm.

• Use licensed Australian bookmakers only. ACMA lets you check whether a gambling operator is legal before you open an account.
• Confirm the markets match. You need the same event, the same market and the same settlement basis at both bookmakers.
• Run the numbers yourself. Add up 1 ÷ each price. A total under 1.00 means a lock. Anything else doesn't.
• Size stakes before you start. Know both amounts so you're not calculating while prices move.
• Place, then verify. Check that each bet slip shows the price and stake you intended.
• Keep records. Note prices, stakes, results and any voids. Your records show what's really happening over time.

On tax, the ATO's ruling IT 2655 looks at when betting might be treated as a business. The ATO's general guidance is that gambling winnings usually aren't taxable for most people. Your circumstances may differ, so get advice if you're unsure.

A service like AUOdds can surface locks and the stake for each outcome. You still place your own bets and check them.

Finally, keep it in perspective. Arbitrage is still gambling, with real money moving through betting accounts, and you must be 18+.

If betting stops feeling controlled and deliberate, help is available. BetStop, the National Self-Exclusion Register, lets you exclude yourself from licensed online and phone bookmakers. Gambling Help Online offers free, confidential support.

Frequently asked questions

Sources

1. Check if a gambling operator is legal, Australian Communications and Media Authority
2. Taxation Ruling IT 2655: gambling and betting winnings, Australian Taxation Office
3. Crypto asset prizes and gambling winnings, Australian Taxation Office
4. BetStop: the National Self-Exclusion Register, Australian Communications and Media Authority
5. BetStop, Australian Government

More guides

• Arbitrage Betting for Beginners: Your First Lock in AU
• Arbitrage Betting Example: 5 Worked Australian Bets
• Compare Odds Australia: Spotting When Prices Lock
• Dutch Betting Horse Racing: Backing the Whole Field

18+ only. Betting involves risk, and prices and limits can change before you place a bet. If gambling isn't fun any more, Gambling Help Online (1800 858 858) is free and confidential, and BetStop lets you exclude yourself from every licensed Australian bookmaker.