Base Rate Scanner
Compare market prices against historical base rates. Spot when the market is diverging from what history says should happen.
RESEARCH TOOL
What does history actually say about this type of event?
What is this?
A "base rate" is just historical frequency. Before you bet on something, the first question should be: "How often has this type of thing happened in the past?" That's your anchor before you go hunting for edge.
This tool pulls historical data on recurring event types — Fed decisions, shutdowns, elections, CPI prints — so you can ground your prediction in reality before the market price sways you.
Real-World Example
→ Before You Bet
A market asks: "Will there be a federal government shutdown in Q2 2026?" It's priced at 28¢. Your gut says that's about right. But what does history say?
Base Rate Finder shows: government shutdowns occur in Q2 roughly 12% of historically measured periods. The market at 28¢ is overpriced by 16 points. That's a NO bet — data-backed.
✅Action: Run Base Rate first. If your gut and the market are both far from history, that's your highest-confidence position.
Bottom line: History repeats more than people think. Know your base rates before trusting your instincts.
Full guide →Quick Answer
the Base Rate Scanner compares current market prices against historical base rates across 12 event categories so you can spot when a market has drifted from its long-run frequency. A base rate is simply how often an event has happened historically — the anchor to start from before adjusting for today's specifics.
Worked Example
Market pricing 26.0pp higher than the 12% historical average. Sample size: 14 observations.
Base Rate Scanner
Sitting presidents seeking a second term win re-election
Market pricing 18.0pp lower than the 68% historical average
Base rates are historical averages, not predictions. Always consider whether this cycle differs from the historical sample.
Use the Base Rate Scanner inside your AI agent
This tool is also live on our MCP server as base_rate_gap. Connect Claude, ChatGPT, Cursor, or Copilot and call it directly — six core calculators are free.
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Related Tools
What is a Base Rate?
A base rate is the historical frequency of an event across many similar situations. If the Fed has held rates in 74% of the meetings where unemployment was below 4%, that 74% is the base rate. It's not a guarantee — it's the starting point for your probability estimate before you factor in what's unique about today.
Markets often ignore base rates. Traders focus on the specific news of the day — the latest CPI print, the Fed chair's tone, what the bond market is pricing — and anchor too hard to recent events. This is the base rate fallacy: treating every situation as unique when the historical pattern is actually highly informative.
When the gap signals a trade
A 10pp gap between the base rate and the market price is significant. It means the market is either dramatically overpaying or underpaying for the event relative to its historical frequency. That's not a trade by itself — you still need a view on why this time is or isn't different. But it's a flag worth investigating, and the bigger the gap, the more you need a specific reason to disagree with history.
Data quality matters
Not all base rates are equally reliable. An incumbent re-election rate built from 22 observations is more trustworthy than a Bitcoin year-end price base rate built from 5 years of data. The scanner shows sample size and confidence level for every category so you know how much weight to give the signal.
Frequently Asked Questions
What is a base rate in prediction markets?
A base rate is the historical frequency of a type of event across many past occurrences. For example, if the Fed has cut rates in 30% of meetings over the last 20 years, 30% is the base rate for a Fed cut. It is the starting point for your probability estimate before factoring in current conditions.
How do I use the Base Rate Scanner to find mispriced Kalshi markets?
Select the event category that matches your Kalshi market (Fed decision, election, GDP, Bitcoin price, etc.), enter the current market price, and the scanner shows you the historical base rate and the gap in percentage points. A gap above 10pp is a strong signal worth investigating further.
When should I trust the base rate over the current Kalshi market price?
Trust the base rate when there is no specific information that makes this event structurally different from past occurrences. If the market is pricing a Fed cut at 20% but the historical rate is 40%, you need a specific reason to believe this meeting is an outlier — not just recency bias from the last few months of data.
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