Google Ads seasonality adjustments: the Black Friday trap

Published October 16, 2026. Black Friday is Friday, November 27, and Cyber Monday is November 30 — the decision below needs making in the next few weeks, not on Thanksgiving.

What the setting actually does

A seasonality adjustment is an advanced Google Ads tool that tells Smart Bidding to expect a specific change in conversion rate for a coming event — for example, "conversion rates will run 50% higher during this three-day sale" — so bids adjust immediately instead of waiting for the system to learn. Per Google's help documentation, it covers Search, Standard Shopping and Display campaigns on target ROAS or target CPA, plus Performance Max and (in beta) App campaigns on all bid strategies.

Two lines in that documentation matter more than the feature itself. Google states that Smart Bidding already manages seasonal events, so adjustments are reserved for major conversion-rate changes. And it time-boxes the tool: ideal for short events of 1–7 days, less effective stretched beyond 14 days. The vendor itself describes a narrow exception tool — not a standard holiday step.

Three BFCM seasons, the same result

Optmyzr's analysis measured each BFCM window (the Wednesday before Black Friday through the Wednesday after Cyber Monday) against a pre-holiday baseline, splitting advertisers into those who set an adjustment and those who did not. The 2024 cut alone covered 5,886 accounts. The year-by-year pattern:

BFCM season	CPC rise — no adjustment	CPC rise — with adjustment	ROAS change — no adjustment	ROAS change — with adjustment
2022	+17%	+36.7%	−2%	−17%
2023	+16%	+32%	−1.5%	−10%
2024	+17%	+34%	+5.7%	−15.7%

Clicks got more expensive for everyone — that is Black Friday, and our Google Ads costs guide shows the baseline CPCs those percentages multiply. But the adjustment group paid about twice the inflation for the same week. In exchange they got more conversion value — an edge that is shrinking: in 2022 their conversion value grew about 25 points more than the other group's; by 2024 the advantage was roughly 6 points, bought with a ROAS swing of more than 21 points.

The third finding explains why the trade keeps getting worse. Among advertisers who set no adjustment, the actual BFCM conversion-rate lift over baseline was 17.5% in 2022, 11.9% in 2023 and just 7.5% in 2024. Shopping has spread across a longer promotional season, so the peak is flatter than it used to be. An adjustment sized from memory — "Black Friday usually lifts us 30–50%" — is now a forecast of an event that no longer happens, entered into a system that believes you completely.

One honest caveat, which Optmyzr states itself: this compares two groups of advertisers, not a controlled experiment — adjustment users may be more aggressive about volume in other ways too. Three consecutive years in the same direction, at this scale, is still a strong signal, not proof.

Why the adjustment backfires

Two mechanisms stack. First, double-counting: Smart Bidding is trained on years of BFCM behaviour platform-wide and reacts to live auction signals as the week unfolds, so your expected lift asks it to anticipate a spike it already anticipates. Second, precision risk: the system applies your percentage at face value from the first auction. Predict a 20% lift, get the 7.5% lift 2024 actually delivered, and you overbid on every auction of the year's most expensive week until someone notices. A wrong target ROAS at least states a price you chose; a wrong forecast states a fact that is not true.

The 2026 readiness data points the same way

Optmyzr's BFCM 2026 readiness report — more than 4,200 accounts and 22,800 campaigns from last year's holiday season — adds the shape of the week itself:

• The four BFCM days are the efficiency trough. ROAS by window: the week before Black Friday, 762% (Performance Max) and 749% (Standard Shopping); during BFCM, 660% and 584%; the week after, 726% and 616%. Conversion rates were the quarter's best, but click costs climbed faster — up 29–46% from the prior week in the report's framing.
• The week before is nearly as good, and cheaper. Standard Shopping converted 6.2% of clicks in the pre-sale week against 6.7% during the BFCM days — a small conversion gap for a much cheaper click.
• The week after quietly drains budget. Standard Shopping's conversion rate sat 7.3% below its pre-BFCM level while its CPC was still 10.2% higher. Performance Max had already cooled (CPC 1.7% below baseline), so the two need separate post-sale reviews, not one blanket cut.

None of that argues for sitting BFCM out. It argues that the money is made in the setup — which products, at what margin, with what exit rules — rather than in a bidding override switched on at the peak.

Do this instead: guardrails, not forecasts

1. Calculate your breakeven target ROAS now. From the Optmyzr report: breakeven ROAS = 1 ÷ gross margin. At a 40% margin, breakeven is 250%. If your normal target is 600%, the band between them is profit you may consciously spend on BFCM volume. If that band is narrow — the report flags a gap under roughly 20% — you may have no room to chase peak volume, and October is when to learn that. Model the spend with our ad cost calculator first.
2. If you want volume, lower the target — directly. A lower target ROAS for the sale window is an explicit price decision. It does not pretend to know the future conversion rate.
3. Clean the conversion signal. If several primary conversion actions count the same purchase, Smart Bidding overbids on inflated value — the adjustment's failure mode, running all year. Keep the strongest purchase source primary and cross-check against GA4.
4. Put the sale price in the feed, early. A discount that lives only in a coupon code leaves Shopping ads showing full price; a feed price that disagrees with the landing page can get listings disapproved, with slow re-approval in peak week. Upload BFCM creative five to seven days ahead for the same reason.
5. Segment by margin and stock. A product at 40% off does not share economics with one at 10% off, and six units of stock do not need a national auction. Separate budgets and targets per margin band stop blended campaigns overspending where profit is thinnest.
6. Write the mid-sale budget rule before the sale. For example: "if ROAS stays 50 points above breakeven and stock supports the sell-through, raise daily budgets 20%." Pair it with alerts — spend ahead of pace, CPC up sharply versus the prior week — so the rule fires on data, not adrenaline.

When a seasonality adjustment is still the right tool

The data does not say "never" — it says "not for events Google already knows." Keep the tool for events with no shared history: your own surprise flash sale, a friends-and-family promotion, a major email or SMS push, or a niche industry moment no platform model has seen. Match Google's conditions: a major expected conversion-rate change, a short 1–7 day window, and a percentage grounded in a comparable event of your own.

Frequently asked questions

Sources & methodology

• MarTech / Optmyzr (October 15, 2026): Seasonality adjustments backfire on Black Friday (three-year BFCM comparison, 2022–2024; 5,886 accounts in 2024; two-group comparison, not a controlled experiment)
• Search Engine Journal: What Optmyzr's three-year study reveals about seasonality adjustments (year-by-year CPC and ROAS figures in the table above)
• Optmyzr (September 2026): Google Ads for BFCM 2026: What 4,200+ accounts reveal (ROAS by BFCM window; breakeven target ROAS method; feed and segmentation checklist)
• Google Ads Help: Create a seasonality adjustment (supported campaign types; Smart Bidding already manages seasonal events; 1–7 day ideal window)

Data checked October 16, 2026. The three-year study compares advertisers who chose to set adjustments with those who did not; it is not a randomised test, and your own account history outranks any benchmark here. ROAS and CPC figures are group averages from Optmyzr's panels, not guarantees for any single account.

Go deeper with AI

This article is the starting point. Copy any of these prompts into your favorite AI assistant to learn more about Google Ads seasonality adjustments and Black Friday bidding costs:

🔎 Run your own breakeven math before BFCM

My store's gross margin is [X]% and my Google Ads campaigns normally target [Y]% ROAS. Calculate my breakeven target ROAS using 1 divided by gross margin, show how much profit band I have between my normal target and breakeven, and tell me whether that band is wide enough to chase extra Black Friday volume. Show the arithmetic step by step and flag anything you are assuming.

🧭 Audit last year's BFCM in your own account

Here is my Google Ads data for [last year's Black Friday week] and the two weeks before it: [paste campaign-level CPC, conversion rate, ROAS and conversion value]. Optmyzr's three-year study found the average conversion-rate lift in the no-adjustment group fell from 17.5% (2022) to 7.5% (2024). Compare my account's actual lift to those figures, name the campaigns behind my biggest ROAS swings, and tell me what conversion-rate forecast — if any — my own data would justify this year.

💡 Write guardrail rules instead of a forecast

Write me a one-page Black Friday guardrail sheet for a Google Ads budget of $[X] per day: (1) my breakeven ROAS is [X]% and my sale target is [Y]%, (2) a mid-sale budget-increase rule written as an if/then sentence, (3) three alerts with numeric thresholds for CPC spikes, budget pacing and conversion-tracking gaps, and (4) a separate post-Cyber-Monday review checklist for Performance Max versus Standard Shopping. Keep every rule to one line so I can act on it mid-sale.

Tip: replace the bracketed parts with your own situation — the more specific your prompt, the more useful the answer.

The bottom line

The seasonality adjustment promises control and delivers a double-counted forecast: across 2022–2024 it roughly doubled CPC inflation and turned ROAS negative every year, while the hands-off group stayed flat or improved — and the real Black Friday conversion lift has shrunk to 7.5%. The 2026 readiness data adds that the week before BFCM converts nearly as well at cheaper clicks, and the week after is where unguarded budgets leak.

The single most important takeaway: do not forecast Black Friday to the algorithm that already forecasts it. Spend October setting the guardrails — breakeven ROAS from your own margin, clean conversions, segmented budgets, written budget rules — and let Smart Bidding drive inside them.

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