Seasonality adjustments in Smart Bidding: capturing the temporary conversion lift in 2026

Google Ads Smart Bidding is built on historical data: the algorithm learns from past performance and adjusts bids based on the expected probability of conversion at any given moment. That works brilliantly during stable periods, but it has one well-known blind spot. When you launch a temporary promotion, run a flash sale, or anticipate a seasonal spike, Smart Bidding lacks enough historical evidence to bid aggressively enough from the very first moment. It reacts with a delay, and during those first hours or even days, you lose conversions and revenue. The solution has a name: seasonality adjustments.

What are seasonality adjustments?

Seasonality adjustments are an advanced setting within Google Ads that allows you to inform Smart Bidding in advance about an expected, temporary change in your conversion rate. You give the algorithm an explicit signal: "Between date X and date Y, I expect my conversion rate to be significantly higher (or lower) than usual." Smart Bidding immediately adapts its bidding strategy accordingly, without needing a learning period first.

This is fundamentally different from simply raising your budget cap or manually adjusting your Target ROAS or Target CPA. With a seasonality adjustment, you provide the algorithm with a conversion rate expectation expressed as a percentage of the historical baseline. If your store normally has a conversion rate of 2% and you expect a conversion rate of 4% during a sale, you set a seasonality adjustment of +100%. Smart Bidding will then raise its bids as if that higher conversion rate were already a reality.

Seasonality adjustments are available for Target CPA and Target ROAS bidding strategies, both at campaign and portfolio level. They are specifically designed for short-duration periods of three to seven days and are not recommended for structural or long-term changes in campaign performance.

Without vs. with seasonality adjustments

What happens during a 3-day promotional period

Without adjustment

• Smart Bidding reacts too slowly to spikes
• Bids too low in the first 24 hours
• Missed impressions during high demand
• Conversion rate increase recognised retrospectively
• Budget inefficiently spread across peak days

With seasonality adjustmentRecommended

• AI anticipates higher conversion rate upfront
• Bids raised immediately at spike start
• Maximum visibility from day one
• Conversion signals processed in real time
• Budget optimally allocated on peak days

The difference between proactive and reactive bidding management becomes clear as soon as you analyse the first day of a promotion. Without a seasonality adjustment, Smart Bidding only accumulates enough signals after 24 to 48 hours to start bidding more aggressively. With a correctly configured seasonality adjustment, your campaign starts with optimal bids on day one. That is exactly the difference between a good promotion and an excellent one.

When should you use seasonality adjustments?

Not every temporary change justifies a seasonality adjustment. Google recommends using them in situations where the conversion rate deviates significantly from the historical average and where the timeframe is limited. The following scenarios are prime candidates:

• Flash sales and discount periods: a 24- or 48-hour sale where urgency drives visitors to convert faster.
• Seasonal product launches: a new model introduced to the market for the first time with an accompanying campaign.
• Black Friday and Cyber Monday: the most predictable peak periods for e-commerce, where conversion rates are structurally higher.
• Holidays and gifting periods: Christmas, Valentine's Day and Mother's Day are classic examples where purchase intent rises sharply.
• Price reductions or extra incentives: free shipping, bundle discounts or cashback promotions that lower the purchase threshold.
• Event-related campaigns: a webinar, open day or product demonstration that temporarily drives extra enquiries.

When should you not use them? If you expect a structural increase, for example because you are tapping into a new audience or permanently introducing a new product, a seasonality adjustment is the wrong tool. In that case, you should adjust your Target ROAS or Target CPA or fundamentally revise the campaign structure.

How to set up a seasonality adjustment

You configure a seasonality adjustment via the Google Ads dashboard under Tools and settings, then Bid strategies, and then Bid seasonality adjustments. The process is short but precise:

1. Give the adjustment a clear name (e.g. "Black Friday 2026 +80%").
2. Set the start and end date. Choose a start time slightly before the actual promotion so Smart Bidding is already calibrated when the spike begins.
3. Select the campaigns or portfolio to which the adjustment applies.
4. Enter the expected conversion rate percentage as a deviation from the baseline. An expected doubling of the conversion rate is +100%; an expected drop of 20% is -20%.
5. Review the settings and save.

A common mistake is setting too long a duration or too high a percentage. If the actual conversion rate differs significantly from what you predicted, Smart Bidding can overbid or underbid, which damages campaign results after the fact. Be as precise as possible in your estimate, based on data from previous comparable periods.

Conversion flow during a promotional period

Percentage throughput per phase (e-commerce benchmark, peak period)

100% Impressions

All impressions during the promotional period

8% Clicks

Average CTR rises to 7-9% during promotions

4% Product page visited

Bounce rate drops with relevant promo landing

1% Conversions

Conversion rate higher due to urgency and offer

Up to 35% higher conversion rate vs. non-promotional periods

A practical guideline: use the conversion rate from the same promotion last year as your starting point. If last year's Black Friday conversion rate was 3.8% against a monthly average of 2.1%, the expected increase is approximately +81%. Round that down conservatively to +75% to allow room for deviations. After the promotion, analyse the actual conversion rate and use it as a calibration point for next time.

Seasonality adjustments for e-commerce and lead generation

For webshops, this is one of the most valuable tools in the Smart Bidding arsenal. Consider ToetsJeKennis.nl, a platform for online exams and courses with an average order value of around 50 euros. During a limited-time offer on exam bundles with a 20% discount, the conversion rate typically rises considerably. Without a seasonality adjustment, Smart Bidding would bid relatively conservatively on the first day of the promotion, because the algorithm has not yet "learned" that this day is different from a normal Tuesday. With a pre-configured seasonality adjustment, the system bids more aggressively from the outset and captures the higher visitor intent immediately.

The same applies to E-4motion.com, the webshop for new electric folding bikes. Around the spring peak in April and May and leading into the festive period, demand for electric bikes rises noticeably. By setting a seasonality adjustment for exactly those weeks, Smart Bidding starts with higher bids precisely when purchase intent is already building, rather than only after the data conclusively prove it.

For lead generation campaigns, the dynamics are slightly different but the principle is the same. Clima-Active.nl, an installer of air conditioning and heat pumps, can see a sharp increase in quote requests when a heatwave is forecast or when subsidy changes for heat pumps are announced. A visitor who was merely browsing may suddenly want a quote tomorrow. By setting a seasonality adjustment in anticipation of such external triggers, Smart Bidding converts that higher request readiness into more leads, at the lowest possible cost per lead.

How AdBrains automates seasonality adjustments

Manually setting up, monitoring and removing seasonality adjustments sounds straightforward on paper, but in practice it demands constant attention, a precise overview of all campaigns, and excellent timing. A single adjustment that is forgotten, set too early, or configured at the wrong percentage costs money immediately. That is exactly why AdBrains has fully automated this functionality through our proprietary AI technology.

Our system uses multiple specialised AI agents that continuously monitor campaign performance and analyse historical conversion rate data. When a client announces a promotional period, or when our system detects an expected spike based on historical patterns, such as the annual Black Friday trend at ToetsJeKennis.nl or the spring peak at E-4motion.com, the AI automatically calculates the correct adjustment percentage based on a year-on-year comparison of the same period.

Our multi-agent verification system then activates: four independent AI agents check the calculated setting before it goes live. This prevents an erroneous estimate from destabilising campaigns. The checks include a review of statistically significant historical data, a verification that the chosen percentage falls within safe margins, a check on the selected campaigns, and a timing check on start and end dates.

Our automatic tCPA/tROAS optimisation module works seamlessly alongside the seasonality adjustments. While an adjustment is active, the AI monitors daily whether the actual conversion rate matches the expectation. If reality deviates significantly, the adjustment is automatically updated or, if necessary, removed mid-campaign. After the promotional period ends, the system removes the adjustment automatically at the configured end time and stores the actual conversion data as a calibration baseline for the next comparable period.

This is reinforced by our server-side signal enrichment via our own sGTM infrastructure. By enriching conversion signals with first-party data, Smart Bidding has access to more accurate signals during the peak period. This amplifies the effect of the seasonality adjustment: the algorithm not only bids higher, but bids smarter on the right users at the right moment.

Seasonality adjustments in practice

Average benchmarks for e-commerce peak periods (industry averages 2026)

+35%

Higher conversion rate during promotional periods

24-48h

Recommended lookahead for Smart Bidding adjustment

+18%

More conversions through proactive bid adjustment

3-7 days

Maximum duration for a seasonality adjustment

The result is a fully hands-off promotion management system where no adjustment is ever forgotten, incorrectly timed or misconfigured. AdBrains clients benefit from systematically higher conversion returns during every promotional period, without ever needing to open the Google Ads interface themselves.

Overview: seasonality adjustments at a glance

The table below summarises the key parameters and recommendations for using seasonality adjustments effectively:

This table makes clear that successfully applying seasonality adjustments requires discipline in planning and execution. The tool itself is powerful, but used incorrectly it can temporarily destabilise your Smart Bidding algorithm.

Frequently asked questions about seasonality adjustments

What is the difference between a seasonality adjustment and a Target ROAS change?

A Target ROAS change tells Smart Bidding what you want to achieve: a higher or lower return per euro spent. A seasonality adjustment tells Smart Bidding what you expect to happen: a temporarily higher or lower conversion rate. The best approach is generally to keep your Target ROAS stable and use only a seasonality adjustment to communicate the expected conversion rate difference. Smart Bidding then adjusts its bids automatically to hit that Target ROAS, taking the higher expected conversion rate into account.

Do seasonality adjustments work with Performance Max campaigns?

Yes, seasonality adjustments are available for Performance Max campaigns. The mechanics are identical to those for Search and Shopping campaigns. Because Performance Max covers a broader channel spectrum including Search, Display, YouTube, Shopping, Gmail and Maps, an accurate estimate is especially important here. Too high an adjustment can lead to overbidding on Display placements that convert less directly.

How accurate does my conversion rate estimate need to be?

As accurate as possible, but a small margin is acceptable. Google advises working from historical data taken from comparable promotional periods. A deviation of 10 to 15 percentage points from reality is generally manageable. Larger deviations can lead to significant budget inefficiency. If you do not have historical promotional data, use a conservative estimate and increase the percentage in future editions based on observed results.

What happens if my conversion rate during the promotion is lower than expected?

If the actual conversion rate falls below what the adjustment indicates, Smart Bidding bids too high and your CPA rises or your ROAS falls temporarily. Smart Bidding detects this gap and begins correcting within 24 to 48 hours, but that takes time. To avoid this, monitor live performance actively and adjust the adjustment mid-campaign if reality diverges sharply from the prediction. At AdBrains, our AI does this automatically: deviations are detected in real time and the adjustment is updated immediately without any manual intervention.