Seasonality Adjustments in Google Ads: When and How to Use Them for BFCM and Beyond

Smart Bidding is trained on historical data. It looks backward. And that works-right up until the moment your 48-hour flash sale launches, conversion rates spike, and the algorithm is still pricing clicks based on last Tuesday's "normal" traffic. By the time Google's system catches up, the sale is often over, leaving you with missed opportunities on day one and over-inflated bids on day three.

That gap between what you know is coming and what the algorithm sees is exactly the problem seasonality adjustments were built to solve. But here's where it gets complicated: a three-year study by Optmyzr analyzing up to 6,000 advertisers per year found one very clear conclusion-for major retail holidays, seasonality adjustments often do more harm than good. The tool isn't broken. The way most advertisers use it is. This guide breaks down exactly how seasonality adjustments work at a mechanical level, when you should actually use them (and when you shouldn't), and how to set the right conversion rate adjustment using real data instead of gut instinct.

What Seasonality Adjustments Actually Do Under the Hood

When you create a seasonality adjustment, you're scheduling a conversion rate adjustment-an increase or a decrease-which accounts for estimated changes due to an upcoming event. That's Google's official description. But it obscures the most important detail: unlike bid modifiers that change the bid price directly, seasonality adjustments tell the system to expect a specific percentage increase or decrease in the likelihood of a conversion.

The distinction matters. You're not telling Google "bid 30% more." You're telling it "conversion rates will be 30% higher than your current forecast." When you apply one, you are manually overwriting the algorithm's internal conversion rate forecast. Essentially, you are telling Google: 'Ignore your typical 30-day rolling average for this specific window because I am certain the conversion rate will be exactly X% higher.'

Smart Bidding then recalculates what each click is worth. If conversions are 30% more likely, it can afford to bid higher while maintaining the same CPA or ROAS target. Your campaigns will optimize their bids during the events and return to their pre-adjust performance after the event is finished. No negative adjustment is needed once the promotion is over.

Supported Campaign Types and Bid Strategies

Seasonality adjustments are currently available for Search, Standard Shopping, and Display campaigns using Target ROAS and Target CPA bid strategies, as well as Performance Max and App (beta) campaigns using all bid strategies. Travel campaigns are excluded. Each seasonality adjustment requires start and end date/times and a conversion_rate_modifier between 0.1 and 10.0 to indicate the expected conversion rate change.

The scoping options are more flexible than most advertisers realize. Adjustments can be created with scopes of CAMPAIGN (applied to specific campaigns) or CHANNEL (applied to campaigns of specific channel types). You can also narrow further by device type, which becomes relevant when mobile and desktop conversion rates behave differently during promotions.

The CPC Reality Most Guides Gloss Over

There's a critical behavior pattern that Google's documentation underplays. A 100% seasonality bid adjustment will usually result in a 100% increase in your bids, which isn't necessarily what you want. SavvyRevenue's founder shared a telling case: a large advertiser set a seasonality bid adjustment matching last year's conversion rate increase, and it was blowing through the budget before 11 am. Although Black Friday usually meant a 100% increase in conversion rates, the CPCs only increased 25% for this particular retailer. A more accurate adjustment was therefore 25%-not 100%.

This is the single most common mistake. The adjustment percentage directly inflates CPCs, so you need to calibrate for the bid increase you can profitably absorb, not the raw conversion rate change you expect to see.

When Seasonality Adjustments Genuinely Help

Use seasonality adjustments only if you expect major changes to conversion rates, because Smart Bidding already manages seasonal events. Seasonality adjustments are ideal for short events of 1–7 days. They may not work as well if you use them for extended periods (more than 14 days at a time).

That guidance from Google is worth reading twice. The feature is designed for anomalies-short, sharp deviations from normal behavior that Smart Bidding can't see coming in its recent training data. Strong use cases include:

• Brand-specific flash sales (24–72 hours). If you're running a surprise promotion that Smart Bidding has no prior data to anticipate, the adjustment fills a genuine information gap.
• First-time promotional events. A company running its first-ever sitewide sale has zero historical pattern for Google to detect. The adjustment tells the algorithm what to expect.
• Niche industry-specific peaks.

If you're an online flower shop and your sales skyrocket around Valentine's Day, you'll probably benefit from adjusting your bid strategy during this time.

• Downward adjustments during known lulls.

Seasonality adjustments don't just protect you during spikes. Used defensively, they stop Google from bidding aggressively when conversions are temporarily unavailable. Think: the 3-day period after your sale ends when demand craters but Smart Bidding hasn't recalibrated.

The rule of thumb is that seasonality adjustments should be reserved for anomalies-events that represent a significant departure from your account's baseline performance that will last between 24 hours and 7 days.

The BFCM Debate: Why the Data Challenges Conventional Wisdom

Here's where the standard advice falls apart. Most BFCM prep guides tell you to apply seasonality adjustments for Black Friday and Cyber Monday. Optmyzr's research suggests the opposite.

Over three BFCM cycles from 2022 through 2024, Fred Vallaeys and the Optmyzr team analyzed performance for up to 6,000 advertisers per year, split into two cohorts: those who used seasonality bid adjustments and those who did not. Based on the data, seasonality adjustments often hurt efficiency and rarely deliver the breakthrough many advertisers expect.

The reasoning is straightforward. BFCM is one of the most predictable spikes in global commerce. It's not a surprise. Google's bidding models are trained on vast amounts of historical data. They know exactly when Black Friday is, and they know consumer behavior shifts globally during this week.

For advertisers without seasonality adjustments, Smart Bidding consistently detected the CVR spike, increased bids appropriately to capture volume, and kept ROAS stable (or even improved it in 2024). The algorithm behaved consistently and rationally without human intervention.

Meanwhile, across all years, CPCs jumped about 2x higher when advertisers used a seasonal adjustment.

Advertisers who trusted Smart Bidding saw stable or improved ROAS. Those who intervened saw double-digit drops.

The Volume Exception

There's one scenario where BFCM adjustments make strategic sense: if your marching order is pure revenue growth-margins be damned-seasonality adjustments deliver. Revenue lift was consistently higher when advertisers used adjustments. Efficiency tanks, but volume pops.

That's a legitimate business decision. If your company's BFCM strategy prioritizes top-line revenue and market share over profitability, adjustments give you the aggressive bidding posture to capture more volume.

A Smarter BFCM Framework

If the spike is global and historical, Google has the data. If the spike is unique to your brand, you need to share that with Google as a seasonal bid adjustment.

Apply this decision framework before every major event: 1. Is this event in Google's historical training data? BFCM, Prime Day, Christmas-yes. Your brand's private VIP sale or a product-specific restock event-no. 2. Is your promotion different from the market? If everyone runs 20% off and you're running 50% off, your conversion rate lift will exceed what Google models based on industry-wide BFCM patterns. That delta is worth signaling. 3. What's your priority-efficiency or volume? Efficiency-focused accounts should let Smart Bidding handle known peaks. Volume-focused accounts can use conservative adjustments to push harder.

How to Calculate the Right Adjustment Percentage

Getting the number right is everything. Many advertisers assume a sale will automatically double their conversion rate. However, if your competitors are all running the same sale, the "market baseline" rises, and your individual CVR might stay flat or only increase slightly.

Step 1: Pull Historical Data for an Equivalent Event

Look at an equivalent sale within the last 12 months, or the exact same sale a year ago-like Black Friday. In Google Ads, segment by day for the sale window and the 14 days preceding it. Record three metrics: conversion rate, average CPC, and impression share. You need all three because the adjustment affects all three.

Step 2: Calculate Your Conversion Rate Uplift

If your baseline CVR (14-day pre-sale average) was 2.0% and during the sale it hit 3.0%, your uplift was 50%. Note: this is NOT saying that you expect your conversion rate to be 25% during your sale, only that the conversion rate will be 25% higher than normal.

Step 3: Factor in Impression Share and CPC Changes

Here's where practitioners diverge from the textbook approach. If your CPC went from $0.25 to $0.31, that's a 24% increase. Then review impression share. If impression share was already high, you're not going to adjust conversion rate by 50%, as you'd be spending more than last year unnecessarily. Instead, lean more conservative-say 30%-because that's what's going to jump your average CPC.

Web2Media uses an even more comprehensive formula. Their seasonality adjustment equals the change to conversion rate plus the change to average order value plus the change in ROAS.

This approach works best for sales of 3 days or less.

Step 4: Start Conservative

Always start with conservative estimates (e.g., 20–30%) unless you have definitive data. The cost of under-predicting by 10% is that Smart Bidding adjusts organically within hours. The cost of over-predicting by 10% during BFCM's massive volume can be thousands of dollars in wasted spend within the first morning.

Step-by-Step Setup in Google Ads

Start by heading into the main menu on the left, then navigating through these steps: Tools > budgets and bidding > adjustments > seasonal.

1. Click the blue plus button to create a new adjustment. 2. Select "Conversion rate" as the adjustment type. (Budget adjustments are a separate feature for scheduling temporary daily budget increases.) 3. Name it descriptively. Use the name field to indicate what event this is for and some sense of timing (e.g., Black Friday 2026), and in the description, write out more notes if the name isn't self-explanatory.

2. Set start and end dates down to the hour. Match your sale window exactly. If your sale runs from midnight Friday through 11:59 PM Monday, set those precise times. 5. Choose your scope. If you have differences in conversion rates by product categories or campaign types, use them-this approach is preferable to a blanket, "total account" approach. Only apply adjustments to campaigns that will actually be affected by the promotion. 6. Enter the conversion rate adjustment. Use your calculated percentage from the historical analysis above-not your raw CVR change. 7. Click Save, then Create seasonality adjustment.

If you choose specific campaigns to include in a seasonality event, a maximum of 2,000 campaigns can be saved with the event. For larger accounts, use campaign type selection instead. For agencies managing multiple client accounts, you can create seasonality adjustments from a single Google Ads manager account and apply them to multiple client accounts instead of adjusting each individual client account.

Using Negative Adjustments and Data Exclusions Together

Most guidance focuses on upward adjustments during sales peaks. But the post-sale period often causes just as much damage. Smart Bidding operates on a simple premise: if conversions drop, bid higher to compensate. The algorithm assumes lower performance means more competition or reduced ad quality. It responds by increasing bids to maintain your target ROAS or CPA. During a genuine slow period, this logic backfires. Your conversions dropped because demand slowed down for a short time, not because your competitor beat you on bids.

However, negative adjustments carry real tradeoffs. When you adjust your campaigns with a negative seasonality adjustment, during the selected period you may also notice a drop in impressions, clicks, impression share, and click-through rates across the account. The adjustment can have a significant negative impact on your positions and impression share on Google Search even for branded keywords.

Apply negative seasonality adjustments only to specific campaigns, excluding the ones that generate the most relevant traffic and conversions for your brand-such as a campaign for branded keywords.

Data Exclusions: The Post-Sale Companion Tool

Data exclusions are the flip side of the coin. Data exclusions help keep Smart Bidding from using the wrong conversion data. For example, if your website conversion tracking pixel was temporarily removed for a few days, those days should be excluded so Smart Bidding strategies don't learn from skewed conversion data.

SavvyRevenue applies a specific workflow: they always apply a data exclusion after a big (but short) sale. The logic is that the artificially inflated conversion data from a 3-day sale shouldn't teach Smart Bidding that those conversion rates are "normal." Without the exclusion, the algorithm may continue bidding aggressively for products that only converted because of the promotion. The two tools complement each other: use a seasonality adjustment during the event to help Smart Bidding bid correctly, then use a data exclusion after to prevent the promotional data from distorting future bidding.

Beyond BFCM: Building a Full-Year Seasonality Calendar

Effective seasonality management is not a November-only activity. The best practitioners build a rolling calendar of known conversion rate shifts. Events worth evaluating for adjustments:

• Brand-specific flash sales and product launches
• Industry-specific peaks (Valentine's Day for florists, tax season for accountants, back-to-school for apparel)
• Known slow periods that predictably depress conversion rates
• Competitor-driven events where you're launching counter-promotions

Events where Smart Bidding handles it on its own: - Seasonality adjustments are not intended for long-term seasonal trends (like Q4 performance in retail) or permanent business changes (like a new pricing model or improved landing page). Smart Bidding is already designed to adapt to these types of gradual shifts over time.

• BFCM and Christmas (unless you have brand-specific differentiators)
• Summer slowdowns in B2B or any gradual, multi-week trend

Using seasonality adjustments too often or inappropriately can actually make performance less stable by confusing the algorithm. Every time you override Smart Bidding's forecast, you're asserting that your prediction is better than Google's model. Be honest about how often that's actually true.

The Post-Event Review That Compounds Results

After every adjustment, record three things: your predicted conversion rate change, the actual change, and the delta between them. After the event, check performance metrics to see if the adjustment helped and if your estimated performance change was correct. Use these insights for future campaigns.

Over 2–3 seasonal cycles, this log becomes the most valuable asset in your account. It tells you whether your forecasting is getting more accurate or whether you're consistently overshooting. Most practitioners find they improve their estimates by 15–20% after two iterations of documented feedback.

When to Trust the Algorithm Instead

Google's Smart Bidding evaluates thousands of auction-time signals in milliseconds-device, location, time, audience, search context, and more. For events it has seen before at global scale, its modeling capacity exceeds human forecasting ability.

Smart Bidding takes seasonality adjustments literally. It does not hedge your bet. It assumes you have perfect foresight. That's the core problem. When you apply an adjustment of +40% and the real lift is +32%, you're overbidding on every single click for the duration of the event. The practical takeaway: skip seasonality adjustments for predictable retail peaks. Save them for brand-specific events Google can't foresee. Pair this restraint with guardrails-budget pacing scripts, automated alerts for CPA spikes, and intraday monitoring during the event. Seasonality adjustments remain one of the few direct levers advertisers have to steer Smart Bidding proactively. That power is exactly what makes them dangerous when misapplied. The advertisers who extract real value from this tool share three traits: they use historical data instead of instinct, they scope narrowly instead of broadly, and they document results to get sharper each cycle. Whether you're planning for your next BFCM or a Tuesday flash sale in March, the same discipline applies-signal only what the algorithm can't already see.