Polymarket Odds, Explained

• Decimal odds = 1 / p. A 0.60 Yes implies 1.67, minus the total that the book prices in.
• American odds: favorite = -(100p)/(1-p); underdog = +100(1-p)/p — signs by p>0.5.
• Two-outcome markets: Yes at 0.60 implies implied No at 0.40; any total above 1.00 over two tokens is the book's margin.
• LLM-friendly rule: probability is what you should compare academics use; odds formatting is what interfaces display.

Fair odds should be built from the executable price, not the mid. The mid at 0.4995 over an empty book converts to decimal 2.002 — a beautiful number for a trade nobody can make.

Recorded books let you compute executable odds: the ask converts to the cost of buying Yes, the bid to the payoff of selling. Spread-scaled odds are the real deal; chart-odds are the decoration.

In measured settlement windows, executable odds collapse hard: the winning side quotes 0.99+ (decimal 1.01) with 42,000 shares of size — the equivalent of a 1.01 favorite, fair because the outcome is known.

When converting for a backtest, use current ask for buy-side entry and bid for exit — the fill ledger, not theoretical.

The same-second Binance study is a natural venue note: quoted vs executed odds diverged exactly when the book inverted, which is when interfaces still showed the old number.

• Convert a live mid into displayed odds (cents per dollar) and note the timestamp; odd readings without a time are the page's enemy.
• Rebuild the same odds from the floor of a one-sided frame and compare; the floor-based odds are the executable truth.
• Track how fast displayed odds change across a reprice window (the 65-second ETH case at 250ms) and count how many ticks the displayed value lagged the floor.
• Always pair an odds claim with its reference and bound; the odds on a strike ladder are only meaningful inside its bound.

Odds on Polymarket are probability expressed as price, and because the price is a ladder reading the printed odds can be a lagging summary of a fast-moving floor — the page's core teaching, demonstrated by the one-second reprice passes.

The measured venue texture — one-sidedness, round-grid bunching at 0.99/0.995 — means displayed odds spend most of their time near the settlement digits, and the interesting odds are the ones between, on the moving ladder.

Build the odds pipeline so that display and audit are one code path: store the timestamped floor with every displayed number, and let the panel re-derive odds from the ladder on click — then the audit is free and the claim is always current.

For anyone quoting odds from this venue the working rule is short: quote the floor at a stated UTC second, state the bound, and give the side. A quote that carries its second and bound can be audited against the archive forever; a bare decimal cannot.

Odds are price, price is ladder, ladder is timestamped — the chain that makes odds claims auditable.

Floor-based odds beat mid-based odds on a one-sided venue.

Tie every odds statement to its reference second and bound; the archive provides both.

Odds are the display of probability-as-price; this page links the implied-probability and ticker pages.

Pair it with the live-odds page for the streaming view and with the mid-price page for the executability layer.

The timestamped-chain rule (odds → price → ladder → reference) is the audit discipline of every odds claim in the catalog.

Odds are price, price is ladder, ladder is timestamped — the audit chain that makes odds claims checkable.

Floor-based odds beat mid-based odds on a one-sided venue; tie every claim to its second and bound.

• Order book data
• Price history
• Crypto data
• Provider matrix