Calendar time is not background noise in prediction markets. As resolution approaches, implied probabilities can creep, pin near extremes, or gap on last-minute headlines—even when nothing “fundamental” seemed to change. Time decay here means how belief and risk compress as the event clock runs out, not options theta—but the intuition rhymes: less time left, less room for recovery.
Payoff is binary: contracts tend toward $0 or $1. A YES at 51¢ with two days left reads as “roughly even with little time for reversal.”
Life phases of a contract
Markets are born long before the public cares. Early listings are often wide, quiet, and narrative-driven—good for research, poor for size. Months out, discovery-phase markets often show wide spreads, modest open interest, and narrative drift. Weeks out, catalysts arrive—debates, filings, data prints—and volume spikes. Days to two weeks out, conviction positioning peaks; spreads may tighten when makers are confident, or widen when binary risk scares inventory. Final hours can pin prices near 90¢ or 5¢ with violent gap risk on surprises. Resolution collapses price to settlement.
Passive buy-and-hold works when edge is about the terminal outcome and you accept path risk through each phase. Active traders map which phase they are in before adding size.
Prediction markets versus stock “decay”
Stocks have continuous payoffs and many drivers. Event contracts have a deadline and a discrete win/lose. The clock changes how much each headline should move implied probability—same evidence, larger price impact when fewer future states remain. Bayesian updating chapters provide the math story; here the trading story is compression.
Implied probability is conditional on time remaining. A 50/50 coin flip with one flip left is not the same as fifty flips left—prediction markets price the flips you still have.
Paths you will see
A slow grind upward might add two cents a week on steady positive news—carry for being right without trading. A bleed downward forces thesis review, not anchoring to entry. Pinning near 88–92¢ signals crowded consensus with limited upside. Lottery contracts at 3–8¢ with days left still embed meaningful implied odds—cheap tickets are often fairly long shots. Last-minute gaps follow debates, court orders, or leaks—the spike chapter applies in endgame too.
Ninety days to seven: a legislation example
Your probability on “bill signed this session” might stay near 55% while the market grinds from 41¢ toward 54¢ over weeks, spreads tighten from four cents to two, and edge shrinks as market price approaches your view. Two days before a cliff vote, spread might blow to five cents on binary fear—chasing the last nickel rarely pays. Time brought the crowd toward you; discipline was holding, not overtrading the calendar.
Edge is not static: as c approaches your p, the trade is “less mispriced” even if you were right all along.
Lottery mistake at three days
YES on a dark-horse primary at 6¢ tempts as “cheap.” If your probability is 12%, expected value can be positive while variance is enormous. Quarter-Kelly still implies tiny dollars. A loss is often priced variance, not bad luck. Tag endgame lottery trades in the journal so monthly review does not call them surprises.
Spread, volume, and open interest near expiry
Final forty-eight hours with eight-cent spreads punish market orders. Volume may surge then collapse into settlement; open interest may fall as traders flatten. Rising OI into expiry without price movement can mean standoff; falling OI with stable price can mean exits before the event.
Scheduled catalysts (debate dates, known release times) compress volatility before and explode after. Unknown ruling dates drift flat then cliff. Oracle dispute risk stretches “time” beyond the wall calendar on some decentralized venues—decay clock and wall clock diverge.
Platform differences
Regulated venues often publish clear close times. Global venues demand careful rule text—ambiguity extends effective horizon. Capped retail with early-exit fees changes effective decay if you might sell before resolution. Play-money rolling markets have fuzzy expiry. Match holding period to venue rules before sizing.
Strategy under clock pressure
Momentum favors catalyst windows; exit before blind pin risk. Contrarian fades need endgame overreaction with real edge, not annoyance at high prices. Arbitrage ties up capital faster as clocks shorten. Hedges on sister narratives belong before the debate spike, not after. Thesis-based stops beat price stops when noise dominates the last day. Portfolio construction should stagger expiries so one night does not wipe multiple correlated lines.
Calendar fields in the journal
Record resolution datetime with timezone from rules, days remaining updated weekly, phase label (discovery, catalyst, endgame), maximum loss if wrong, and any date-bound invalidation. Endgame rules many traders use: no new lottery size above a tiny bankroll slice; higher edge bar in the last seventy-two hours; prefer limits; flatten when edge is smaller than spread.
Hedging into binary week
A long YES on a candidate win with debate in five days might pair with a partial hedge on a sister contract (win margin, party control) to reduce joint narrative risk. Spread on the second leg is a cost; doing it before the spike is usually cheaper than after.
Scheduled versus unscheduled clocks
A known debate date compresses volatility into the hour after the stage, not evenly across the month. An unknown court ruling drifts flat until docket noise, then cliffs. Macro calendars repeat a recognizable rhythm—CPI weeks look like CPI weeks. Oracle dispute risk on decentralized venues stretches effective time: the event happened but settlement did not, and prices can hang in limbo.
Treat “days to expiry” on the UI and “days to truth” in the rules as cousins, not twins.
Core concepts to remember
Time changes how much news should move price. Edge shrinks as market c approaches your p. Liquidity often worsens when you need it in endgame. Lottery tickets are often fairly long shots. Calendar metadata belongs in every journal row.
Common misconceptions
“Nothing happened so price should be flat.” Decay alone can move odds. “I will get out tomorrow” near expiry is a market order prayer. “High price means safe.” Pinning is crowded risk, not safety. “Decay does not apply to me because I am long-term.” Resolution is a hard deadline for everyone.
Passive holders and path risk
Buy-and-hold is not free of calendar risk. A correct terminal view can mark you wrong on paper for weeks if the path whipsaws through wide spreads. Passive edge must be large enough to absorb path pain, or you need liquidity to add on dips—liquidity that may not exist in endgame.
What comes next in this module
Time decay sets the edge bar by phase. Comparison and consensus chapters assume you know when liquidity lies; mispricing audits explicitly score decay before execution. Treat the calendar as a first-class input beside price.
A contract at 8¢ with one week left is not the same bet as 8¢ with six months left—the implied odds match the clock. Always read expiry before calling a price “cheap.”
Resolution rules sometimes allow early settlement or voids—read the contract for whether “time” includes reporting delays. A market can look “stuck” at 95¢ while legal challenge risk remains—decay toward certainty is not the same as decay toward 100¢ until rules say so.
Traders who ignore the calendar often discover spread and liquidity risk in the final week, when edge is smallest and friction is largest. Decentralized oracles can extend risk beyond the headline date.
What comes next
Single-market time series are half the picture. The same real-world event often trades in multiple places at once.
Next: Comparing Multiple Markets for the Same Event