Seasonality adjustments in Google Ads - what they do and when to use them

Google's smart bidding algorithms are good at adapting to gradual changes in performance patterns. They are less good at anticipating sudden, short-term shifts. A Black Friday sale, a 48-hour flash promotion, or a seasonal demand spike that lasts two weeks can all cause the algorithm to react slowly - spending too conservatively at the start of a spike or continuing to bid aggressively after it ends. Seasonality adjustments give you a way to inform the algorithm in advance.

How seasonality adjustments work

You set a date range and a predicted conversion rate change - for example, "from 25 November to 28 November, conversion rates will be 40% higher than the historical baseline." Google's smart bidding uses that adjustment to bid more aggressively during the specified period, anticipating the higher conversion likelihood rather than waiting to observe it. Once the period ends, the algorithm returns to normal bidding behaviour.

When to use them

Short promotional events of one to seven days are the intended use case. Flash sales, bank holiday promotions, seasonal peaks for specific product categories, or event-driven demand spikes. They are not designed for gradual seasonal trends - smart bidding handles those through its normal learning process. And they are not appropriate for changes lasting more than a few weeks, where adjusting your Target CPA or ROAS target directly is a better approach.

Getting the percentage right

The adjustment percentage should be based on data where you have it. If you have a previous year's conversion rate during the same promotional period, use that to calculate the uplift. If it is a new promotion, make a conservative estimate based on comparable events. An adjustment that is too aggressive can push bids so high that your CPA becomes commercially unviable for the duration. Start conservative and increase if results justify it.

A note on Performance Max

Seasonality adjustments apply to Target CPA and Target ROAS campaigns including Performance Max. For PMax specifically, the adjustments interact with the campaign's existing learning. If you have recently made significant changes to your PMax campaign, adding a seasonality adjustment on top can create unpredictable behaviour. Apply adjustments to stable, well-optimised campaigns where the baseline behaviour is predictable.