Quick answer
Bid-ask spread: The bid-ask spread is the difference between the highest price a buyer will pay and the lowest price a seller will accept.
Also called: spread (exchange sense)
Explained, with an example
Example: best bid $0.34, best ask $0.40 → spread $0.06; tighter spreads mean more liquid markets [1] [2]. For a trader, crossing the spread is a cost, much like a sportsbook's Overround. Do not confuse it with a Point spread, which is a handicap line in sports betting.
Formula
spread = best ask − best bidTry it: tools and tutorials
Frequently asked questions
What is a bid-ask spread?
The bid-ask spread is the difference between the highest price a buyer will pay and the lowest price a seller will accept.
About this guide
Pred-Data publishes independent, source-linked explainers about prediction markets and the AI tools used around them. Every factual claim on this page links to a primary or reputable secondary source, checked on the date shown above. We do not run a trading venue, take bets, or give personal advice.
Author: Ken Lin · Corrections: if you spot an error, we review it and date-stamp the fix.
Affiliate disclosure
Some links on this site (marked “Partner link”) may be affiliate links: if you sign up through them we may earn a commission at no extra cost to you. Partner links use rel="sponsored nofollow" and never change our assessment. Platform links in our comparison tables are plain, non-affiliate links to official sites.
Sources
- Prices & Orderbook — Polymarket Documentation, accessed 2 Nov 2026
- CFTC Glossary (binary option, DCM, order book, liquid market, market maker, settlement, wash trading, arbitrage, hedging) — U.S. CFTC, accessed 2 Nov 2026