What to check before you touch anything
- Does your business have clear year-over-year seasonality? Compare the current period not just to last month but to the same period last year, to tell a seasonal effect apart from a structural problem.
- How far in advance is the seasonal peak or slowdown known? Planned events (sales, holidays, industry-specific demand spikes) are different from unpredictable swings, in that you can prepare for them ahead of time instead of just reacting.
- How did the relationship between CPC and conversion rate behave during the same season last year? Competition typically drives CPC up for everyone during a peak season at once — that's not a sign your campaign is underperforming.
- Does the "need" to revisit target CPA line up with a one-off spike that will fade on its own in a few weeks? A sharp target change to react to a temporary event can create more instability than the seasonality itself.
- How well does a target CPA set during the slow season actually apply during peak season, and vice versa? If the cost-of-acquisition gap between seasons is large and predictable, a single year-round target may be the wrong setup from the start.
Possible approaches
- For businesses with clear, predictable seasonality, many agencies build a seasonal calendar in advance and deliberately loosen target CPA ahead of peak periods (sometimes using Seasonality Adjustments in Google Ads for short, sharp expected spikes), rather than waiting for the strategy to visibly struggle in real time.
- Google recommends using Seasonality Adjustments specifically for short, sharp, and predictable spikes (a 1–3 day sale), not as an ongoing tool for managing the target — for longer seasonal periods, that's really just a regular manual budget/target adjustment.
- If the seasonal period is long and predictable (say, an entire high-demand quarter), rather than adjusting the same target ad hoc, it's often better to have two (or more) pre-set target CPA values ready for the high and low season and switch between them on a calendar.
- You can treat a seasonal rise in CPA as a temporary, acceptable trade-off if it's offset by volume (say, during peak season the business is happy to accept a higher CPA in exchange for a much larger number of sales) — the move then isn't to "fix" the number but to deliberately widen the acceptable target range for that period.
- It makes more sense to revisit target CPA based on a sustained gap between the target and the auction's reality over several weeks in a row, rather than on a calendar cadence like "once a quarter." Seasonality is a reasonable explanation for short-term swings, but it shouldn't be used as an excuse to ignore a long-term trend entirely.