What is a portfolio bid strategy in Google Ads?

After you create one, Google says it is stored in your Shared library, the central location for managing your portfolio bid strategies and tracking their performance, and that portfolio bid strategies were previously referred to as flexible bid strategies. The alternative is a standard strategy: Google describes Target CPA, for example, as available either as a standard strategy applied to a single campaign or as a portfolio strategy that can apply to multiple campaigns.

A few things change with it. On Target CPA, Google says that with a portfolio strategy your campaigns, ad groups and keywords are optimised collectively for a single target, and that bid limits are only available for portfolio, not standard, Target CPA bid strategies. Its bid strategy report follows the portfolio too: if a campaign is part of a portfolio, Google says you'll be directed to the bid strategy report for the entire portfolio bid strategy. And on shared budgets, Google says that if a Maximise clicks, Maximise conversions or Maximise conversion value strategy shares a budget with another bid strategy, your bid strategy status might show as misconfigured, and that to prevent this, all campaigns in the same shared budget should be utilising the same portfolio bid strategy.

Our reading, not Google's: a portfolio makes one target do the work of several, so before grouping campaigns, check they count the same conversions. A target is a price per whatever the Conversions column counts, and campaigns counting different things share a number that means something different in each.