Polymarket spread explained: bid, ask and displayed price

A bid expresses buying interest; an ask expresses selling interest. With illustrative bid 0.48 and ask 0.54, the absolute spread is 0.06 per share. For 20 shares, the price gap is 1.20 if those levels remain available.

That calculation describes two offers rather than a completed gain or loss. Actual results require fills and expenses. Do not compare one outcome’s bid with another contract’s ask simply because the same asset appears beside both numbers.

Polymarket describes its displayed price as the bid-ask midpoint, switching to the last trade when the spread exceeds 0.10. A visible percentage therefore need not represent an offer to execute an arbitrary quantity at that price.

In our example, the midpoint is 0.51 while the nearest ask is 0.54. The 0.03 gap reflects the midpoint’s location. If the book changes after capture, recalculate with the new levels and their current observation time.

A difference of 0.06 corresponds to 6 cents and 6 percentage points on the probability scale. It is not a 6% change relative to 0.48. That hypothetical relative change would be 0.06 / 0.48 = 12.5%.

Label comparison units. A spread of 6 points with bid 48 and ask 54 is clearer than an isolated 6%. This makes the arithmetic checkable and prevents confusing a book’s width with changes in the estimate over time.

The spread separates opposing prices, while a fee follows execution rules. Combining them requires a clearly defined example of one operation. A larger quantity can also cross several levels and change the average price beyond the initial best ask or bid.

Identify the outcome, record both best prices and quantities, then assess the relevant size and expenses separately. A narrow spread with tiny available size does not establish a large executable quantity. Continue with the liquidity guide for that distinction.