Bid vs Ask on Prediction Markets: How to Read the Spread and Set Orders That Don't Overpay

Every contract carries two prices, one to buy and one to sell, and the gap between them quietly decides how much of your edge survives. Ten minutes here saves you money on every trade you ever make.

Open any contract on Kalshi or Polymarket and look closely. The headline number might say 62¢, but the trading screen shows something like 61¢ / 63¢. Two prices. Everything in this article is about that pair of numbers: what they mean, who sets them, and how to trade so that the gap works for you instead of against you.

We'll follow one running example the whole way: a contract on tonight's home team, currently quoted 61¢ bid, 63¢ ask.

The two prices, plainly

The bid (61¢) is the highest price anyone is currently offering to pay. If you want to sell right now, this is your price.

The ask (63¢) is the lowest price anyone is currently willing to sell for. If you want to buy right now, this is yours.

Notice the built-in asymmetry: the moment you buy at the ask, the most anyone is offering for your contract is the bid. Buy at 63¢ and you are instantly holding something you could only sell for 61¢. You did not lose a coin flip; you paid the spread.

The spread is that gap, 2¢ here. Think of it as the price of immediacy. Trading right this second, guaranteed, costs you the spread. Being patient can cost you nothing.

Where the numbers come from

Nobody at Kalshi or Polymarket sets these prices. Both platforms run an order book, a live list of offers from actual traders. Some people have standing offers to buy at 61¢, others standing offers to sell at 63¢, and there are more offers stacked behind those: buyers at 60¢, at 58¢, sellers at 64¢, at 66¢, and so on down and up the ladder.

The bid and ask you see are just the best offer on each side at this moment. When news hits, traders yank and replace their offers, and the pair of numbers jumps. That is all a price move is: the front of the line changing.

This matters because it means the spread is not a fee the platform charges. It is a negotiation you are allowed to join, and your order type decides how you take part in it.

Market orders vs limit orders: the whole game

Every platform gives you two ways to trade, whatever it calls them on screen.

A market order says: fill me now, at whatever the other side is asking. You buy at the 63¢ ask, done in one tap. You pay the spread in exchange for certainty and speed.

A limit order says: here is my price, fill me if someone meets it. You post an offer to buy at 61¢ or 62¢, and you wait. Maybe seconds, maybe hours, maybe forever. You risk missing the trade in exchange for choosing your own price.

Run the example both ways. You want 100 contracts of the home team.

• Market order: filled instantly at 63¢. Cost: $63.
• Limit order at 61¢: you join the bid. If a seller comes down to meet you, you get filled at 61¢. Cost: $61.

Two dollars on a $63 trade is about 3% of your position, and you make the same choice again on the way out. Cross the spread on both ends of every trade and you are giving away roughly the spread's width twice per round trip, before the outcome of the game has said a word. On a 2¢ spread that is manageable. On the wide spreads you'll find in smaller markets, it can be the difference between a winning and losing strategy all by itself.

The default that serves you well: limit orders when you can wait, market orders only when the situation is moving and being in (or out) matters more than the last cent or two. Pregame position you've thought about all day? Limit order, always; there is no rush. Live contract spiking while you're trying to take profit on a swing? That is what market orders are for, and the spread is a fair price for the exit.

Buying NO is selling YES

One mechanic trips up almost everyone at first. Each contract has a YES side and a NO side, and they are mirror images: the two prices always sum to a dollar, minus the spread. If YES trades at 62¢, NO trades around 38¢.

So there are two ways to express "I think this price is too high": sell YES contracts you own, or buy NO contracts fresh. Economically they are the same position. Practically, it means you never need to own something before you can trade against it. Think an 80¢ favorite is really a 65% proposition? Buy NO at roughly 20¢. If you're right and the price sags, your NO contracts appreciate cent for cent.

Once this clicks, the platforms stop looking like a menu of things to predict and start looking like what they are: one price per event, tradeable from either side.

Reading the spread like a signal

The spread is also free information. Before you trade any market, glance at it:

Tight spread (1-2¢): an active, competitive market. Plenty of traders on both sides, easy to enter and exit near fair value. The big game markets look like this, especially close to game time.

Wide spread (5¢ or more): a thin market. Few participants, and the standing offers are cautious. Wide spreads are where market orders do real damage, and where a limit order placed mid-spread will often get filled by the next impatient person who arrives. In thin markets, be the patient side.

A widening spread during a live game tells you something too: uncertainty just spiked and traders pulled their offers. Right after a scoring play or a review, spreads gape for a few seconds while everyone re-prices. Firing market orders into that gap is the single most expensive habit in live trading. If you know the moment is coming, decide your price before it hits. (How far prices can jump on a single play, and why, is its own article: why prediction market prices swing so hard.)

The mistakes, so you can skip them

1. Market-ordering thin markets. The 8¢ spread on an obscure futures contract is a toll booth. Limit order or walk away.
2. Chasing spikes. Buying with market orders during the seconds after big news fills you at the panic ask. The price that matters is the one after the book refills.
3. Anchoring on the last trade. The "last price" you see may be minutes old in a slow market. The bid and ask are the only prices you can actually transact at.
4. Leaving stale limit orders open. An order you posted before news broke is a gift to whoever picks it off after. If the situation changed, your resting orders should too.
5. Ignoring the spread when sizing an edge. If you think a contract is 3¢ mispriced and the spread is 4¢, you do not have a trade. Your edge has to clear the round trip.

The bottom line

Two prices, always. You sell at the bid, you buy at the ask, and the gap between them is a cost you control. Limit orders when patience is cheap, market orders when speed is worth paying for, and never trade a spread wider than your edge. Watch a live chart during one big game with all this in mind, on capper.app or on the platforms themselves, and you will start seeing the order book for what it is: the thing you are actually trading against.

Related reading: How prediction markets work · Prediction market liquidity · Why prices swing so hard · Hedging in action: the Travelers story

Educational information, not financial advice. Prediction markets involve risk of loss, and their legal status varies by location and changes over time.