Build up before the peak, not during it
The preparation window decides the peak. Launch campaigns and push feed updates weeks before the season starts, so the algorithms have conversion data before the traffic surge arrives rather than learning in the middle of it. A campaign entering peak season with history bids intelligently from day one; a campaign launched into the surge spends its most expensive weeks guessing.
The same logic covers practical readiness: stock on bestsellers confirmed, promotions loaded, and budgets approved in advance. Peak season rewards accounts that finished their work early and punishes the ones still building while the traffic is already paying premium prices. Most peak-season failures are decided in the calm weeks before it, when preparing was still cheap.
Manage through the peak, cut after it
During peak, expect higher CPCs as competitors crowd into the same auctions. Protect your bestsellers first, and accept that efficiency targets differ from a quiet month's: paying more per click is rational when conversion rates and order values run higher than usual. Google's seasonality adjustments help for short, sharp events like a flash sale.
After the peak, cut deliberately rather than riding declining demand at full budget. The weeks after a season quietly drain accounts that keep spending as if the surge were still on. The demand curve fell; the budget should follow it down on purpose.
Judge with the right comparison, change in the right season
Use year-over-year data, not last month, to judge seasonal performance. Comparing December to October tells you about the calendar, not the account; comparing December to last December tells you whether the account improved.
The most common seasonal mistake is launching big changes during peak season. Restructures and new strategies trigger learning phases, and learning during peak means paying the year's highest CPCs for the algorithm's education. Big changes belong in quiet months, when data is cheap and mistakes are small, so the structure is proven before the expensive traffic arrives. The calendar repeats every year, which makes seasonality the most predictable variable in the whole account.