PG-0005 Update | September 23, 2026

When ProbGap last updated its U.S. Q3 GDP forecast, the market was at 51% and we were at 64%. Now the market has climbed to 74%. Here's what changed — and why we're keeping our forecast unchanged for now.

Market: 74% | ProbGap: 64% | Gap: −10 pp

On September 18, ProbGap updated its forecast for U.S. real GDP growth of at least 3.0% in the third quarter of 2026.

At the time, the prediction market assigned the outcome a 51% probability. Our forecast was 64%, creating a positive gap of 13 percentage points.

Five days later, the picture looks very different.

Polymarket now prices the outcome at approximately 74%. That's a 23-percentage-point increase from our previous reference price.

The market hasn't simply caught up with ProbGap. It has moved past us.

Our previously published 64% forecast now sits 10 percentage points below the market.

The most important fundamental indicator is the Atlanta Fed's GDPNow model.

Its September 17 estimate puts annualized U.S. real GDP growth for Q3 at 5.1%, comfortably above the prediction market's 3.0% threshold.

The model rose from 4.4% on September 10 to 5.1% on September 16, reflecting stronger estimates for consumer spending and government expenditures.

That provides a plausible fundamental explanation for increased market confidence.

But a GDP nowcast is not the same as the probability of exceeding a specific threshold in the official release.

The final result remains sensitive to incoming economic data, model uncertainty and revisions to the underlying estimates.

ProbGap's latest published forecast remains 64%.

We don't automatically revise our probabilities when market prices move. A material forecast change should be supported by a fresh assessment of the underlying evidence.

The Atlanta Fed's 5.1% estimate is a meaningful signal. But it was already published on September 17, before our September 18 forecast update.

The market's subsequent repricing is worth documenting. On its own, however, it isn't a new economic data release.

For now, we're maintaining our previous forecast while reassessing the evidence.

The next scheduled GDPNow update is September 25.

We'll examine whether the incoming data support the market's increased confidence or reveal reasons for caution.

The market's current 74% probability also creates a new benchmark against which to evaluate our forecast.

If the evidence justifies a material revision, we'll publish it and preserve the earlier forecast in our history.

The market moved from 13 percentage points below our forecast to 10 points above it.

That reversal is worth documenting, regardless of which estimate ultimately proves closer to the outcome.

The purpose of our track record is to show not just our initial forecasts, but how they evolve — and how they compare with market prices over time.

PG-0005 remains open. Our latest published forecast is 64%.

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