On September 10, the IAB released its 2026 Outlook Study September Update. Full-year U.S. ad spend growth is now forecast at 12.3%, per the study — up from the 9.5% projected in January. That's a 2.8-point revision on a market that touches every auction you're competing in.
If your budget was finalized in Q4 of last year, you built it to compete in a 9.5% growth environment, per the January IAB forecast. You're now in a 12.3% one.
Why the first half overperformed
The IAB surveyed more than 200 brand and agency ad investment decision-makers for this update. The study found the revision reflects two cyclical drivers: the Winter Olympics and FIFA World Cup, both of which pulled forward major media investment in Q1 and Q2. On top of that, the macroeconomic headwinds that had buyers planning conservatively in January didn't hit as hard as feared.
Both factors pushed spending higher. When spending goes up market-wide, auction prices follow.
Where the revisions hit hardest
The aggregate 12.3% figure matters less than the channel breakdown.
Social media growth was revised to 16.5%, per the IAB study — 1.9 points above the 14.6% January forecast. CTV was revised to 15.6%, up from 13.8%. Commerce media comes in at 13.6% per the same report. All three are running above the overall market average.
Those aren't small adjustments. If you set your social or CTV allocation against a 14–14.6% growth backdrop, per the January forecast, you're now underweighted in the channels that tightened the most. The auction you're in is more competitive than the one you budgeted for.
The customer acquisition shift nobody planned for
The study found that customer acquisition jumped nine percentage points to 63% as a stated media goal since January. Brand equity rose six points to 43%, per the same report.
This tells you something about what's driving CPM pressure in Q3 and Q4. When 63% of the market is explicitly optimizing for new customer acquisition, the cost of reaching cold audiences goes up independently of your budget size. You're not just bidding against more spend. You're bidding against more intent.
If your prospecting campaigns haven't been refunded since January, the competitive environment they're running in has changed underneath them.
What 86% of buyers are preparing for
86% of buyers expect AI to change how they measure media within the next year, per the IAB study — a number that doesn't have an immediate budget implication but carries a 12-month one.
This isn't abstract. It means attribution methodology is in active flux — last-click is losing ground to modeled and data-driven models, AI Max and Advantage+ are making more bidding decisions than campaign managers are, and the signal-to-noise ratio in standard platform reports is getting harder to interpret without a clear measurement framework underneath it.
If you're heading into Q4 with an unchanged attribution setup, you're making spend decisions with a lens most of the market is already questioning.
Four things to check before Q4 planning closes
Look at whether your social and CTV budgets are proportional to a 16–17% growth environment, per the revised IAB forecasts, not a 14% one. The gap matters most in prospecting auctions.
Check whether your customer acquisition campaigns are funded relative to your retargeting. The 63% acquisition intent share, per the study, means more competition for cold audiences — your cold-to-warm budget split should reflect that.
Audit your attribution setup before Q4 spend goes up. If 86% of buyers, per the study, expect AI to change measurement in the next 12 months, the time to build a reliable baseline is before November.
Compare your year-over-year spend growth rate to 12.3%, per the revised IAB forecast. If you're growing slower than the market, you're losing relative share even when absolute numbers look fine.
If you want a clear read on where your account stands before Q4, a free audit through Gromerce surfaces the budget split and attribution gaps that tend to compound under pressure.
The market grew faster than the plan. The question now is whether your Q4 strategy accounts for that.
Sources: PR Newswire, September 2026
