Bidding constraint scenarios
A campaign operates under two numbers you control: the daily budget and the target (CPO or ROAS). Depending on which one is currently the limiting factor, the campaign sits in one of four scenarios. The bidding model reads the situation and bids accordingly.
Before you start
- A campaign configured with an objective, a target, and a daily budget. See Set the bidding objective and target.
The four scenarios
Budget-constrained
The campaign regularly spends its daily budget, and the target would allow higher bids if there were more budget to spend.
What the bidding model does: concentrates spend on the keywords most likely to convert within the target, and holds back on keywords that would absorb budget with weaker unit economics.
What you'll see: cost per result stays close to the target; the keyword mix shifts toward stronger performers.
Target-constrained
The campaign has budget headroom, but the target is tight. Higher bids are available, but they would push cost per result above the target.
What the bidding model does: keeps bids at the level that holds the target, even if budget goes unspent.
What you'll see: spend runs below the daily cap; volume is lower than it could be at a looser target.
Both constrained
The campaign hits the daily budget and the target at the same time. Every adjustment is a trade-off.
What the bidding model does: raises bids on keywords with headroom against both, and lowers bids on keywords using budget without hitting the target.
What you'll see: small, frequent adjustments rather than big swings. The campaign is at capacity — bigger gains require moving the target or the budget.
Neither constrained
The campaign has both budget and target headroom.
What the bidding model does: looks for keywords where a higher bid could capture volume that is still inside the target. It does not fill the budget for its own sake.
What you'll see: spend grows over time as confidence in keywords builds, not in a single step.
What this means in practice
A scenario is not a setting you pick — it describes what the campaign is doing right now. Campaigns move between scenarios as the daily budget changes, competitors enter the auction, or seasonality shifts conversion rates. The two levers you have are the target and the daily budget. See Set the bidding objective and target for how to change them.