About PredictLedger

PredictLedger is a ledger for the calls people make on prediction markets. You log a position on a Kalshi or Polymarket market, the market resolves it, and the ledger scores your judgment with the same tools forecasting tournaments use: the Brier score, calibration and skill against the market price, plus plain profit and loss.

Who makes it

PredictLedger is built and operated by 9GG LLC, a small software company in Wyoming that runs a portfolio of focused web and mobile tools. Operator: 9GG LLC, 9GG LLC, 30 N Gould St, Ste R, Sheridan, WY 82801, USA. Support: [email protected].

What it is for

• Traders who want an honest, dated record of their own calls instead of a memory that flatters them.
• Forecasting hobbyists who want a Brier score for real-money positions, not just tournament questions.
• Writers, analysts and researchers who want a public track record they can link to.

What it is not

It is not a trading venue, a tipping service or a signal feed. It does not place orders, hold money or connect to anyone's exchange account. It is not affiliated with Kalshi or Polymarket; their names identify the public data sources only. Nothing here is investment, trading or gambling advice. Read the disclaimer and data & attribution pages.

How scoring works, in one paragraph

Each call implies a probability: buying Yes at 62 cents says you think the chance is above 62%. When the market resolves we compute the Brier score of that implied (or stated) probability, compare it with the market price at the moment you logged the call, bin your calls to draw a calibration curve, and sum the money result. Ranks need at least 10 resolved calls. Details on the methodology page.

Updated November 1, 2026.