The Vig You Don't See: How Bid-Ask Spreads Quietly Eat Your Edge

The Casino You Didn't Notice

Prediction markets don't charge vig the way sportsbooks do. There's no -110 stapled to every line, no juice baked into the moneyline. So people assume they're trading in a clean, efficient environment where price equals price.

They're not. The vig is still there — it's just hiding in the bid-ask spread.

When a market shows YES at 62¢ and NO at 40¢, the implied probability adds up to 102%. That extra 2% is the market maker's cut. And on thin markets, that spread can blow out to 5, 10, even 15 cents wide. You just don't feel it until you try to get out.

The Math That Hurts

Let's say you buy YES at 62¢ on a contract you think is worth 65¢. Feels like a 3¢ edge, right?

Now check the bid. If someone hit you with a market sell right this second, you might only get 58¢. Your "edge" is actually a 4¢ hole you have to climb out of before you're breakeven.

To make money, one of two things has to happen: the true probability has to move enough to overcome the spread, or you have to hold to resolution. Anything in between and you're paying the market maker to be there.

Why Spreads Widen When You Need Them Tight

Spreads aren't fixed. They breathe with the market. And they always breathe the wrong way for you.

When news breaks: Market makers pull quotes because they don't want to be the sucker holding stale prices. The spread you saw at 2¢ wide is suddenly 8¢ wide right when you want to trade.

On weekends and overnight: Fewer participants, thinner books, wider spreads. Great time to get filled at terrible prices.

In small markets: A market with $5K in daily volume might have a permanent 6¢ spread. That's not inefficiency — that's the cost of anyone being willing to make a market at all.

Right before resolution: Ironically, spreads often widen as certainty increases, because nobody wants to be picked off by someone with better info in the final hours.

The Round-Trip Test

Before you enter any position, ask yourself one question: if I had to exit right now, what would it cost me?

Look at the bid, not just the ask. Multiply the spread by your position size. That's your minimum cost of being wrong — and often your minimum cost of being right if you need to exit early.

A $1,000 position in a market with a 5¢ spread costs you $50 just to round-trip. Your edge better be bigger than that or you're literally just donating.

How to Actually Fight Back

Post, don't take. Instead of hitting the ask at 62¢, put a bid in at 60¢ and wait. You become the market maker. Sometimes you don't get filled. That's fine — the trades you didn't make at bad prices are worth as much as the ones you did make at good ones.

Use limit orders religiously. Market orders in thin books are a confession that you don't respect your own money.

Size to the spread. In tight markets (1-2¢), you can trade aggressively. In wide markets (5¢+), you need a much bigger edge to justify the entry, and you should probably plan to hold to resolution.

Track your fill quality. Over a month, compare your average entry price to the midpoint at time of order. If you're consistently paying 2¢ over mid, you're leaking money you'll never see on any P&L screen.

The Uncomfortable Truth

Most losing traders don't lose because their picks are bad. They lose because they pay the spread on the way in, pay it again on the way out, and do that fifty times a month. Death by a thousand 3¢ cuts.

The market makers aren't smarter than you. They're just patient enough to let you come to them.