91% — Who will be the Lightweight Title Holder on Dec 31, 2026
Leader: Justin Gaethje at 91% · Kalshi 91% · 4 contracts · $6K volume · medium confidence
Updated 2026-09-22 00:23:58 UTC

Tracks the leading outcome in a winner-take-all prediction market set with 4 outcomes.

Why this matters:
This probability estimates that Justin Gaethje will hold the UFC Lightweight title on December 31, 2026. The 92% price reflects his current status as champion, with roughly four months remaining for the title to change hands through either a scheduled bout or unexpected circumstances. The main drivers of this level are the typical timeline for title defenses in the UFC and the competitive field among challengers. The biggest catalyst would be any scheduled lightweight title fight before year-end; if no fight is announced in the coming weeks, the probability would likely remain elevated. Conversely, if Gaethje is booked against a top contender with a short turnaround, market pricing could shift based on fighter odds and injury risk.

Key factors:
- Gaethje must defend or retain the title through December 31, 2026—roughly 3.5 months away
- UFC title fights typically require 2-3 months of notice; lack of an announced bout suggests low probability of a defense occurring before year-end
- The runner-up probability (4%) suggests one specific contender or outcome; identify which challenger is being priced as most likely to dethrone Gaethje
- Injury or medical suspension of Gaethje or any scheduled challenger would directly affect both the title holder outcome and timeline
- Historical UFC lightweight title vacancy patterns and typical defense frequencies inform baseline expectations for divisional activity

Contracts:
- Who will be the Lightweight Title Holder on Dec 31, 2026?: Justin Gaethje — 91¢ Kalshi $1K (weight 18%)
- Who will be the Lightweight Title Holder on Dec 31, 2026?: Mauricio Ruffy — 9¢ Kalshi $153 (weight 2%)
- Who will be the Lightweight Title Holder on Dec 31, 2026?: Arman Tsarukyan — 4¢ Kalshi $4K (weight 57%)
- Who will be the Lightweight Title Holder on Dec 31, 2026?: Ilia Topuria — 4¢ Kalshi $2K (weight 24%)

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## Methodology

SimpleFunctions aggregates live YES-side prices from Kalshi and Polymarket contracts bound to this question. For binary topics the headline is the liquidity-weighted mid-price (weight = log(1 + 24h volume) × freshness, where freshness is 1.0 if updated <24h, 0.7 if <7d, 0.4 otherwise). For multi-outcome (winner-take-all) topics the headline is the current leader's price — disjoint outcomes are never arithmetically averaged. Snapshots refresh every 5 minutes during market hours.

## SF Signal

- SF Index, regime, and 30d Brier calibration are computed separately and surfaced at https://simplefunctions.dev/admin/calibration.
- No SimpleFunctions index / regime / calibration signal is bound to this topic yet — the headline above is market-derived only.

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*Last verified: 2026-09-21T23:21:02.566Z*

By SimpleFunctions — https://simplefunctions.dev/

Cite as: "91% per prediction markets (SimpleFunctions, September 2026)"
Canonical: https://simplefunctions.dev/answer/ufclightweighttitle
Full data: https://simplefunctions.dev/api/public/query?q=Who%20will%20be%20the%20Lightweight%20Title%20Holder%20on%20Dec%2031%2C%202026
Provider: SimpleFunctions — https://simplefunctions.dev