If you've ever checked your Google Ads account and found your campaign burning through 5x, 10x, or even 20x its stated daily budget, you're not alone — and you're not going crazy. This is one of the most jarring experiences for PPC practitioners at every experience level, and it's a topic that surfaces regularly in the r/PPC community. A €50/day Display campaign suddenly charging €500 in a single day isn't a glitch — it's the result of several deliberate (and sometimes poorly documented) Google Ads mechanics working simultaneously against an uncapped bidding strategy. This post breaks down exactly why it happens, what Google's actual policies say, and most importantly, how to stop it from happening again.
Before we get into fixes, let's establish the baseline: Google Ads does not guarantee your daily budget will be your daily spend. It never has. What they do promise is a monthly spend cap — your daily budget multiplied by the average number of days in a month (30.4). This is called monthly spend protection, and it's the only hard ceiling Google commits to.
In practice, this means Google can spend up to 2x your daily budget on any given day to "make up" for days when traffic was lower than expected. So a €50/day campaign could legitimately spend €100 in a single day under normal Google Ads policy.
So how does a campaign go from a 2x allowance to 10x actual spend? That requires several factors stacking on top of each other, which is exactly what's happening in the scenario described — a Display campaign using Maximize Clicks with no maximum CPC bid cap.
This is the core culprit, and it's something that burns practitioners far more often than it should. Here's the mechanic:
When you select Maximize Clicks as your bidding strategy and leave the "Maximum CPC bid limit" field blank, you are effectively handing Google a blank check for individual auction bids. The algorithm's only objective is to generate as many clicks as possible within your budget — and with no per-click ceiling, it can (and will) bid whatever it calculates will win inventory.
On the Google Display Network (GDN), this becomes especially dangerous because:
On Search campaigns, query volume naturally limits how fast budget gets consumed. If nobody searches your keywords, you don't spend. Display has no such natural throttle. A Display campaign can find millions of eligible impressions within seconds of a targeting match. When Maximize Clicks is running uncapped against that unlimited inventory, the spend acceleration can be dramatic — especially in the early days of a campaign when the algorithm is still calibrating.
In my experience managing large-scale Display campaigns, I've seen freshly launched GDN campaigns with smart bidding burn 300-400% of their stated daily budget in the first 48-72 hours. The algorithm is effectively "exploring" — and exploration is expensive.
As mentioned, Google caps your total monthly spend at your daily budget × 30.4. A €50/day campaign should never exceed €1,520/month. But here's where many practitioners get tripped up:
A common question in the r/PPC community is whether there's a way to set a truly hard daily cap. There isn't — not natively in Google Ads. But there are several layers of protection you can stack to dramatically reduce budget blowouts.
This is the single highest-impact change you can make right now. In your campaign settings under Maximize Clicks, there's an optional field for "Maximum CPC bid limit." Use it.
What CPC cap should you set? Start by calculating your acceptable cost-per-click based on your conversion goals. If you don't have conversion data yet, use competitive benchmarks:
| Display Campaign Type | Typical CPC Range | Suggested Starting Cap |
|---|---|---|
| Broad audience targeting | €0.10 – €0.80 | €0.50 – €1.00 |
| In-market audience targeting | €0.30 – €1.50 | €1.00 – €2.00 |
| Remarketing / retargeting | €0.15 – €1.00 | €0.75 – €1.50 |
| Custom intent audiences | €0.40 – €2.00 | €1.50 – €2.50 |
A Max CPC cap doesn't prevent Google from bidding aggressively — it prevents any single click from costing more than your defined limit. On a €50/day budget with a €1.00 Max CPC, you'd need at least 50 clicks to exhaust your daily budget, which is a much more controllable situation.
If you're running a small budget Display campaign (<€100/day) and don't have significant historical conversion data (fewer than 30-50 conversions in the past 30 days), smart bidding strategies like Maximize Clicks are operating largely blind. The algorithm needs data to calibrate, and while it's learning, it will overspend.
Manual CPC on Display gives you explicit control over every bid. Yes, it requires more active management — but on a €50/day budget, the risk of an uncapped smart bidding strategy going sideways outweighs the convenience benefit.
Shared budgets can help distribute spend across campaigns more predictably, but they don't create hard caps either. Use them when you have multiple campaigns that should share a pool and you want Google to allocate based on performance — not as an overspend prevention mechanism.
Google Ads has built-in alerting and automated rules that can act as a safety net:
The limitation here is that automated rules only run at their scheduled frequency — hourly at best. If your campaign burns €200 in 45 minutes, a rule running every hour won't catch it in time. This is why the Max CPC cap (Step 1) is so critical — it's a preventative control, not a reactive one.
For agencies or practitioners managing multiple accounts, tools like Optmyzr, Skai (formerly Kenshoo), or even Google's own Scripts can monitor spend in near real-time and pause campaigns more responsively than native automated rules. A custom Google Ads Script checking spend every 15-30 minutes is often more effective than relying on Google's hourly rule execution.
If you've already experienced significant overspend and believe you've been charged beyond the monthly cap (daily budget × 30.4), you have recourse:
In my experience, Google support is generally cooperative about honoring the monthly cap policy when you present clear documentation. The key is knowing the policy exists and asking specifically for a billing adjustment rather than a vague "I was overcharged" complaint.
Beyond the immediate fixes, there are campaign architecture decisions that can significantly reduce your exposure to budget overspend:
Counterintuitively, if you're worried about overspend, setting a lower daily budget and monitoring more frequently is often more effective than setting a higher budget and hoping for the best. Google's overspend allowance is proportional to your stated budget — a €25/day budget can be overspent by a maximum of €50/day (2x), whereas a €50/day budget can technically overspend to €100/day before hitting the 2x ceiling.
If you're running a campaign that serves on both Search and Display (via "Search Network with Display Expansion" or similar), your budget management becomes significantly more complex. Keep Search and Display campaigns separate — it gives you independent budget controls and makes overspend much easier to diagnose and address.
As practitioners often discuss in the r/PPC community, Maximize Clicks is one of the least sophisticated bidding strategies available — it's purely volume-oriented with no quality signal. For Display campaigns, consider:
If you're currently experiencing (or want to prevent) a 10x daily budget overspend on your Google Display campaigns, here's your concrete action plan:
Budget overspend on Google Ads isn't inevitable — it's the predictable result of specific configuration choices running into specific platform mechanics. Understand those mechanics, add appropriate guardrails, and you can run Display campaigns that stay close to your intended budget without sacrificing performance.
