Common beginner mistakes

The YES ask includes half the spread, so it always overstates the probability. On a market quoting YES 64¢ and NO 40¢ the honest reading is 64 ÷ 104 = 61.5%, not 64%. Two and a half points does not sound like much until it is the whole of a supposed edge.

This mistake compounds when comparing venues, because each one’s raw price carries a different amount of overround. Two venues quoting YES at 64¢ and 62¢ may be 1.3 points apart rather than 2, or closer still. Divide first, compare second, every time.

The midpoint is the honest probability estimate and it is not a price you can trade at. On a market bid 55¢ and asked 65¢, the midpoint says 60% and buying costs 65¢. Paying 65¢ for something you have valued at 60¢ is a losing trade at the moment of execution, whatever happens afterwards.

Wide spreads are also where the temptation is strongest, because wide spreads live on neglected markets and neglected markets are where a new participant is most likely to feel they have found something. The feeling is often correct and the trade is still bad: the edge has to be larger than the cost of entering, and on a ten-point spread that is a high bar.

The title is a search term; the criteria are the contract. Markets that look identical can settle on different dates, against different sources, with different treatment of the awkward cases. A view that is right about the world and wrong about the wording pays exactly nothing.

The habit that fixes this takes two minutes: think of the messiest plausible outcome, then check whether the text says what happens in that case. If it does not, you have found a risk that is not in the price for you — and often the reason the price looked wrong in the first place.

A visible gap between two venues is not an opportunity until it survives what capturing it costs: half of each side’s spread on each leg, plus each venue’s fee, plus whatever it costs to have funds sitting on both. A five-point gross gap against four points of cost is not a business.

Across a play-money boundary it is not an opportunity at any size, because there is no trade. Mana cannot fund or hedge a dollar position, so a fifteen-point gap between a play-money price and a real-money one can persist forever with nobody able to close it. That is not an inefficiency; it is two different things being measured.

And even between two real-money venues, the two contracts have to be the same contract. Different resolution wording on the same event is the most common explanation for a persistent gap, and it is a reason the gap is correct rather than capturable.

Contracts are indivisible, so $100 at 68¢ buys 147 contracts for $99.96, not $100 of exposure. Small here, and the habit matters: computing return as stake ÷ price − stake overstates profit on every trade where the division is not exact.

The related and larger error is sizing on the payout rather than the loss. The number at risk is the whole committed amount, because a binary contract can go to zero with no partial recovery. A position sized against its potential profit is a position whose downside was never examined.

Money committed to a contract resolving in eighteen months is unavailable for eighteen months. That is why long-dated contracts on near-certain outcomes trade well below certainty, and why buying them expecting a quick, safe few cents is a misunderstanding of the instrument: paying 97¢ for a dollar in two years is roughly 1.5% a year.

A portfolio of long-dated positions is also much less liquid than it looks. Exiting early means selling into whatever bid exists, which on a quiet long-dated market can be several points below the midpoint.

The most expensive mistake on this list is not analytical. Increasing position size after a loss to get back to even is a pattern that has nothing to do with any view about any event, and it is the one that turns a bad month into a serious problem.

The instrument makes it easier than most, because settlement is frequent, markets are always open, and the next contract is always available at a price that looks like a chance to fix things. If any of this is familiar, our responsible trading page lists the warning signs and where to get help. It is not a decision we are qualified to advise you on, and it is the one that matters most.