The AIA/Deltek Architecture Billings Index (ABI) fell to 44.7 for September 2026, down 2.5 points from 47.2 in August and up 1.4 points from 43.3 in September 2025. The American Institute of Architects published the figure on October 21. The ABI is a diffusion index, a score built from the share of firms reporting higher billings against the share reporting lower billings, so 50 means no change and a score below 50 means more firms billed less than the month before. AIA says September had the largest share of firms reporting declines since May. The score sits below the 12-month average of 46.9 and ranks fourth lowest of the 13 months shown, above only September 2025, January 2026 and May 2026. (That makes the year-over-year gain a comparison against the lowest month in the table.)
Billings fell further below 50 in September
AIA/Deltek Architecture Billings Index, national score as first reported (50 = no change)
| Month | ABI score | Change from prior month (points) |
|---|---|---|
| Sep 2025 | 43.3 | |
| Oct 2025 | 47.6 | 4.3 |
| Nov 2025 | 45.3 | -2.3 |
| Dec 2025 | 48.5 | 3.2 |
| Jan 2026 | 43.8 | -4.7 |
| Feb 2026 | 49.4 | 5.6 |
| Mar 2026 | 49.8 | 0.4 |
| Apr 2026 | 48.3 | -1.5 |
| May 2026 | 44.5 | -3.8 |
| Jun 2026 | 47.3 | 2.8 |
| Jul 2026 | 46.6 | -0.7 |
| Aug 2026 | 47.2 | 0.6 |
| Sep 2026 | 44.7 | -2.5 |
What moved
The two forward-looking indexes moved apart. Project inquiries rose to 53.2 from 50.8, so more firms saw new project inquiries than saw fewer. The design contracts index, which tracks the value of newly signed design contracts, dropped to 43.7 from 48.3. In August the two indexes were 2.5 points apart, and in September the gap was 9.5 points.
By region, the Northeast fell to 39.1 from 40.7 and stayed the weakest. The South had the largest regional drop, to 43.1 from 46.1. The West came in at 50.7 and the Midwest at 50.6, which AIA describes as stable conditions.
By firm specialization, multifamily residential fell 4.9 points to 42.9, the largest move in the detail. Commercial/industrial firms rose to 50.9, which AIA counts as modest growth for a second consecutive month. Institutional firms came in at 47.6 and mixed-practice firms at 41.5, both still in decline.
| Measure | August 2026 | September 2026 | Change (points) |
|---|---|---|---|
| National ABI | 47.2 | 44.7 | -2.5 |
| West | 49.8 | 50.7 | 0.9 |
| Midwest | 50.7 | 50.6 | -0.1 |
| South | 46.1 | 43.1 | -3.0 |
| Northeast | 40.7 | 39.1 | -1.6 |
| Commercial/industrial | 50.4 | 50.9 | 0.5 |
| Institutional | 47.0 | 47.6 | 0.6 |
| Multifamily residential | 47.8 | 42.9 | -4.9 |
| Mixed practice | 42.5 | 41.5 | -1.0 |
| Project inquiries | 50.8 | 53.2 | 2.4 |
| Design contracts | 48.3 | 43.7 | -4.6 |
AIA also reported backlogs at architecture firms for the end of the third quarter. The average was 6.2 months, down from 6.6 months at the end of the first quarter. Large firms with annual billings of $5 million or more held at 8.1 months, and firms with an institutional specialization held at 8.0. Small firms with billings under $250,000 went from 3.1 months to 3.8. Multifamily firms had the sharpest drop, from 6.2 months in March to 4.8 months in September.
AIA Chief Economist Richard Branch pointed to a soft economy, harder project financing and more cautious clients. “With fewer projects moving forward, there is little reason to expect a meaningful improvement in business conditions in the near term,” he said.
How to use this number
AIA says the ABI predicts nonresidential construction activity 9 to 12 months ahead. So September’s design billings relate to work that could start from roughly mid-2027 into the third quarter of that year. That timing is a reading of the data, and AIA’s release gives no regional or sector forecast.
Two uses for a contractor:
- If you build multifamily, put the sector score and the backlog figure next to your own count of multifamily bid invitations for the last six months. A sector score of 42.9 and design backlogs down to 4.8 months both point to fewer projects coming out of design. If your invitation count is holding steady while those two fall, the drop may not have reached your market yet, or you are winning a larger share of a smaller pool. Your win rate by month separates the two.
- Track the design contracts index against your own preconstruction pipeline. Inquiries count interest, and design contracts count owners who signed with an architect. A simple match on your side is the number of pursuits where the owner already has a design contract in place. If that count falls in step with the index over the next quarter, the national figure is a usable early read for your region. If it does not, use the regional score for your area in its place.
Revisions and caveats
AIA does not label the monthly score as preliminary. The September release puts August at 47.2, the same as first reported. AIA does revise past months. December 2025 was first published at 48.5, and AIA’s January 2026 release put it at 47.1. The pages opened for this post do not explain that revision, so the chart and table use each month as first reported, and the month-over-month changes carry the same caveat.
The regional and sector scores are three-month moving averages, and AIA notes they may not average out to the national score. The September multifamily reading of 42.9 therefore includes July and August survey responses. The national score counts the direction of each firm’s billings and ignores the size of the change, so 44.7 says more firms billed less without saying by how much.
The index comes from AIA’s Work-on-the-Boards survey of architecture firm leaders, which AIA says has run for over 20 years. The pages opened for this post do not give the number of responding firms or a margin of error, so a one-month move is best read alongside the 13-month trend.