Portfolio-style budget reallocation across campaigns

Portfolio-Style Budget Reallocation Across Campaigns

Applies to an account with enough live history to compare campaigns against each other, not to a brand-new build with no data yet.

The play

1. Model the account as one budget envelope, not a set of independent silos. The question isn't "does this campaign deserve more budget" in isolation — it's "given a fixed total, which campaign returns more for the next dollar."
2. Read impression share lost to budget as the primary signal for underfunded campaigns — it directly shows demand the account is missing because the budget cap, not the auction, is the limit. Pair it with each campaign's marginal cost-per-conversion at current spend, not just its average, since averages hide campaigns that are efficient at low spend and expensive at the margin.
3. Cap any single reallocation at roughly 20-30% of a campaign's budget per move. Bigger single jumps outrun what Smart Bidding can absorb cleanly and create a fresh learning period right when you need stable data to judge the change.
4. Keep protected minimums outside the optimization — brand campaigns and any geography or line of business with a standing floor get funded first, regardless of where they'd rank on pure marginal return.
5. For a known short-term demand spike (a launch, a flash sale, a 1-7 day event), separate two different levers and don't conflate them: raising the budget cap can start several days early so there's headroom once demand shows up, but a conversion-rate seasonality adjustment should start exactly when the shift begins — never days in advance "to be safe" — and always carry a hard end date matched to when the event ends.
6. Consolidate campaigns running too little volume for reliable signal before optimizing across them; a marginal-return comparison built on thin data is a guess wearing a spreadsheet.

What good looks like

• The best reallocation plans move budget toward impression-share-limited campaigns before they move budget away from anything — funding real missed demand beats cutting a campaign that merely looks less efficient on average.
• The common mistake is starting a seasonality bid adjustment early "just to be safe." That pays inflated costs for normal-intent traffic during the run-up and is functionally the same error as forgetting to set an end date — both quietly burn budget outside the window that actually mattered.
• A good plan states the size of each shift as a percentage, the signal that justified it, and what happens to protected minimums — a plan that just says "move budget to the winners" hasn't done the portfolio work.

Rules

• MUST treat impression share lost to budget as the primary underfunded-campaign signal, not raw ROAS ranking alone.
• MUST cap individual budget shifts to roughly 20-30% per adjustment period.
• NEVER start a conversion-rate seasonality adjustment before the actual demand shift begins, and never leave one running without a hard end date.
• NEVER compare marginal return across campaigns with too little conversion volume for the numbers to mean anything — consolidate or wait for data first.