Shared budgets in Google Ads: when to use and when to avoid

Budget management is one of the most underestimated levers in Google Ads. How you distribute your budget across campaigns directly determines how many impressions, clicks and conversions you extract from every invested euro or dollar. One of the options Google Ads provides for this is the shared budget: a single pooled daily budget that is automatically distributed across multiple campaigns. It sounds efficient, and it can be, but only under the right conditions. This article explains exactly what shared budgets are, when they are a smart choice, when they can harm your campaigns, and how AdBrains uses its own AI technology to take budget management to the next level.

What are shared budgets in Google Ads?

A shared budget is a budget pool you create in the Shared Library of Google Ads and then link to two or more campaigns. Instead of each campaign having its own separate daily budget, the system automatically draws from the same pool. Google distributes the available budget based on expected performance: the campaign that sees the most opportunities at any given moment receives a larger share.

This differs fundamentally from individual budgets, where you set a hard daily cap per campaign. With an individual budget, you know exactly what each campaign can spend at most. With a shared budget, you give Google more freedom to shift between campaigns, with the expectation that this leads to better overall performance.

Shared budgets are available for Search, Display, Shopping and Video campaigns. They are not available for Performance Max (PMax) campaigns, which always require their own budget. This is an important detail to account for when structuring your campaigns.

How does budget distribution work in practice?

Google adjusts the distribution of a shared budget daily based on auction dynamics, search volume and historical performance. On a day when one campaign sees a strong increase in relevant search queries, it can claim a larger share of the budget. Another campaign experiencing less demand on the same day automatically receives less. This is sometimes referred to as dynamic budget allocation.

A concrete example: suppose you run two campaigns for Clima-Active.nl, which provides air conditioning and heat pump installations. One campaign focuses on air conditioning (stronger in summer) and one on heat pumps (stronger in winter and early spring). With a shared budget, Google can shift the majority of the budget to the AC campaign in the summer months and to the heat pump campaign in winter. That is a textbook example of when a shared budget makes sense.

However, the mechanism only works well if the campaigns involved represent a comparable value per conversion. As soon as campaigns have significantly different ROAS targets or CPA objectives, the automatic shifting can actually be counterproductive.

When does a shared budget work well?

There are clear situations where shared budgets provide genuine value. The most important ones are:

• Comparable campaign objectives: If two or more campaigns pursue the same end goal (for example, quote requests with a comparable CPL), a shared budget is more efficient than manually adjusting each campaign.
• Strongly fluctuating demand by season or day: For campaigns where demand fluctuates significantly by day or season, a shared budget prevents one campaign from using up its budget while another has an empty pool.
• Limited total budget: If you distribute a small total budget across multiple campaigns, a shared budget can prevent budget fragmentation from weakening performance. Instead of giving each campaign a mini-budget, the best-performing campaign automatically gets more room.
• Campaigns with comparable bidding strategies: Shared budgets perform best when all linked campaigns use the same or similar Smart Bidding strategies, such as Target CPA or Target ROAS.
• Testing comparable campaign variants: In A/B tests of campaign structures or ad copy, where the objective is identical, a shared budget can make the experiment fairer.

For ToetsJeKennis.nl, an online webshop for exams and courses, a shared budget could work well for two comparable Search campaigns that both target the same type of searcher: students who want to take an exam. If both campaigns pursue a comparable Target ROAS and the average order value is equal, Google can distribute the budget smartly based on daily demand.

When should you avoid shared budgets?

Just as important as knowing when shared budgets work is knowing when they can harm your campaigns. There are situations where a shared budget does more harm than good:

• Brand versus non-brand campaigns: Your brand keywords typically have a much lower CPC and higher Quality Score than generic keywords. If you combine brand and non-brand campaigns in a shared budget, there is a risk that Google allocates too much budget to the cheaper brand campaign, while the non-brand campaign actually needs more budget for volume.
• Campaigns with very different ROAS or CPA targets: If one campaign targets a tROAS of 500% and another targets 200%, a shared budget makes little sense. Google may shift the budget to the campaign with the lower ROAS target, reducing overall efficiency.
• Campaigns at different funnel stages: Awareness campaigns (top-of-funnel) and conversion campaigns (bottom-of-funnel) have fundamentally different objectives. Placing them together in a shared budget creates confusion in the Smart Bidding algorithm.
• Performance Max campaigns: PMax campaigns do not support shared budgets. If you use a hybrid structure with both PMax and Search campaigns, you need to manage the budget split manually or through AI.
• Campaigns with very different geographic targeting: If one campaign runs nationally and another only regionally, the demand dynamics are so different that shared budget management becomes inefficient.
• Situations where per-campaign transparency is essential: If you need to report on budget spend per campaign to a client or internal stakeholder, shared budgets make reporting more complex.

Practical overview: shared budget or not?

How AdBrains AI automates and improves budget management

Manual budget management is time-consuming and error-prone. Especially in accounts with multiple campaigns, fluctuating seasonal influences and different objectives, it is virtually impossible to manually determine the optimal distribution every day. This is precisely where the AI technology developed in-house by AdBrains makes a structural difference.

AdBrains operates a multi-agent verification system in which four independent AI agents check every budget decision before it is implemented. This means a reallocation decision is never based on a single signal. One agent analyses conversion volume, a second looks at auction dynamics and search volume, a third evaluates the tROAS or tCPA performance of each campaign, and a fourth checks whether the proposed adjustment fits within the client's strategic objective. Only when all four agents agree is the adjustment applied.

In addition, the AdBrains AI applies automated tCPA/tROAS optimisation at campaign level. Rather than using shared budgets as a blunt instrument for budget distribution, the AI analyses daily which campaign generates the most conversions per invested euro, and adjusts the daily budget per campaign individually. This delivers the benefits of dynamic allocation without the drawbacks of a standard shared budget, such as loss of per-campaign control.

The AI also continuously monitors for underspend and overspend. If a campaign structurally fails to spend its daily budget, the system detects this within 24 hours and adjusts the budget strategy or issues a recommendation to deploy the budget elsewhere. The same applies to campaigns that are consistently hitting their budget limit: the AI flags budget restrictions as a conversion-suppressing signal and automatically escalates this to the campaign manager.

For clients such as Clima-Active.nl and E-4motion.com, where specific conversion goals are central, the AdBrains AI ensures that the available budget flows at all times to the campaigns and ad groups delivering the lowest cost per lead or the highest ROAS. This is not a one-time configuration but a continuous process optimised daily based on up-to-date conversion data. Advertisers who benefit from this AI-driven approach see on average 34% less budget waste and a 28% higher ROAS compared to manually managed shared budgets.

Want to learn more about our approach and what investing in AI-powered campaign management looks like? Our werkwijze and pricing pages cover everything you need.

Shared budgets versus Smart Bidding: a common source of confusion

Many advertisers confuse shared budgets with Smart Bidding. These are two fundamentally different concepts. Smart Bidding is a bidding strategy that Google uses to determine the optimal CPC or CPA for each auction. Shared budgets are about distributing the total available daily budget across campaigns. The two can coexist, but they operate at different levels.

It is perfectly possible to link campaigns using Target ROAS (Smart Bidding) to a shared budget. But the golden rule still applies: ensure that the tROAS targets are comparable, otherwise the shared budget disrupts the signal quality that Smart Bidding needs to function optimally. Smart Bidding learns at the campaign level, and if a campaign receives significantly less or more budget than expected due to shared budget reallocations, this can extend or disrupt the learning period.

Frequently asked questions about shared budgets in Google Ads

Can I combine a shared budget with Performance Max campaigns?

No, Performance Max (PMax) campaigns do not support shared budgets. PMax campaigns always require their own separate daily budget. If your account contains both PMax and Search campaigns, you need to manage the budget distribution manually or through an external automation tool. AdBrains AI monitors the balance between PMax and Search budgets daily and adjusts individual budgets based on conversion performance.

Does a shared budget affect the Smart Bidding learning period?

Yes, indirectly. Smart Bidding learns at the campaign level. If a shared budget causes a campaign to receive significantly less budget than expected on certain days, this can lower the conversion rate and extend the learning period. It is therefore advisable to implement shared budgets only after campaigns have completed their learning period and built up stable conversion data.

How do I report on budget spend when using a shared budget?

Google Ads still shows actual spend per campaign in the campaign columns, even when using a shared budget. You can therefore analyse per campaign how much of the shared budget was actually allocated to it. In the Shared Library you can also view the total consumption of the shared budget as a whole. For more detailed reporting, a connection with Google Looker Studio or an external BI platform is recommended.

What is the difference between a shared budget and a portfolio bid strategy?

A shared budget manages budget distribution across campaigns. A portfolio bid strategy manages bids across campaigns, where Google optimises bids to achieve a shared goal (for example, Target CPA or Target ROAS) for the entire portfolio. The two tools are complementary: you can link campaigns to both a shared budget and a portfolio bid strategy, but this only makes sense if the campaigns have a comparable objective. Never use them together for campaigns with fundamentally different goals.