Will U.S. existing home sales decline more than 10% year-over-year in any month through September 2026?

Q1 2026 housing market grew +1.5% YoY per Compass disclosure — directional opposite of the >10% decline trigger. Refi transactions +100% YoY indicates rate environment favorable enough to drive significant volume. Purchase transactions +4% YoY confirms underlying demand. The resolution window has 6 months remaining (April-September 2026); January's -4.4% reading is the only soft month and was attributed to weather. The probability of any single month showing >10% YoY decline requires an exogenous shock (rate spike, recession trigger) rather than continuation of current trajectory. Compass framing 4.1M existing home sales as 'trough' implies management view of near-bottom — supportive of base case. Probability shifts modestly lower from 0.20 to 0.15 reflecting favorable backdrop while preserving tail risk.

While Q1 actuals are favorable, the resolution window is 'any single month from February 2026 through September 2026' — and February-March readings (likely already in NAR data) align with Compass's +1.5% Q1 framing. Six monthly readings remain (April-September 2026). Single-month volatility in NAR SAAR can spike from base-effect dynamics or short-term policy events. The Fed funds path through summer, potential mortgage rate spike from inflation re-acceleration, or rate-shock from a credit event are all conceivable. Year-ago comparisons (Apr-Sep 2025) were generally weak per pre-merger reporting, so base effects are mostly favorable for the YoY comparison — but a single shock month is plausible. 0.17 reflects modest tail-risk preservation.

The strongest data point from Q1 2026 is refi transactions +100% YoY — an order-of-magnitude signal that mortgage rates are at levels supporting transaction recovery. Compass and broader market data both showing positive YoY growth in Q1 establishes that the housing market is in expansion mode entering the spring/summer resolution window. The structural setup makes a >10% decline during peak transaction months (April-September) unlikely without a discrete shock. Sibling market comp-2026-zillow-trial resolved NO at Brier 0.04 — supports holding adverse-event probability low when structural setup contradicts. 0.14 reflects favorable base case with modest tail preservation.

Q1 2026 housing market growing +1.5% YoY combined with rate-sensitive refi activity +100% YoY paints a clear picture: the rate/affordability environment is favorable, and demand is responding. The question is whether any single month between April-September 2026 prints a >10% YoY decline. Given the favorable tailwinds and Compass framing 4.1M sales as trough, the central case is continued positive YoY growth or mild deceleration. Tail-risk scenarios: (1) sudden rate spike from inflation surprise, (2) recession trigger from external shock, (3) base effect distortion from prior-year extremes. None of these are visible in current data. 0.15 reflects favorable backdrop and disciplined tail preservation.

Six monthly NAR readings between April and September 2026 each have nonzero probability of printing >10% YoY decline. Even if base case central tendency is +1-3% YoY growth, single-month volatility (from holiday calendar shifts, weather events, regional weather, or local market stress) can produce headline decline numbers. NAR SAAR has historically printed >10% YoY decline in non-recession months when comparing against unusually strong year-ago periods. The unconditional base rate of any single month in a 6-month window printing >10% decline given a +1-3% trend is moderate — call it 10-15% probability. 0.17 reflects this base-rate awareness on top of favorable trend.

Compass's strong Q1 market characterization combined with Rocket partnership delivering 1% rate discount to buyers creates compounding favorable conditions. The 580 bps brokerage GTV outperformance and 20 consecutive quarters of organic outperformance show Compass execution above market — meaning the market itself is also growing. With existing home sales already at the company-claimed trough of 4.1M annualized, year-ago comparisons (which were also depressed) provide a low base making YoY comparisons mathematically more likely to be positive. Probability shifts to 0.14.

Q1 market grew +1.5% YoY per Compass disclosure. Refi +100% YoY confirms favorable rate environment. Purchase +4% YoY confirms demand. Resolution window has 6 readings remaining; current trajectory is favorable. Tail risk is exogenous shock. Probability shifts modestly lower from 0.20 to 0.15.

Favorable Q1 backdrop reduces ambient probability of >10% decline trigger but 6 monthly readings remain and single-month volatility persists. NAR SAAR historically shows month-to-month volatility even in stable periods. Probability sits at 0.16 reflecting modest tail risk.

Trough-level year-ago base, +1.5% Q1 trajectory, +100% refi YoY, Rocket rate discount support. All structural indicators favor continued positive YoY growth. Probability drops to 0.14 reflecting strong favorable backdrop and disciplined tail preservation.