If your ABO (Ad Set Budget Optimization) campaign is spending significantly more than the set daily budget — like hitting $90 on a $50/day cap — that’s not expected behavior, especially without Advantage+ features enabled. Here are the most likely causes:
1. Campaign is set to “Daily Average” instead of a strict daily cap
Meta sometimes spends over the daily budget on high-performing days, with the intention to "average out" over a week.
2. Billing Event Delay or Reporting Lag
Sometimes Facebook reports spend late, especially near the end of a billing cycle or if you're making changes rapidly.
3. Multiple Ad Sets Sharing the Same Budget (CBO confusion)
Make sure this is a true ABO setup and not a CBO campaign being mistaken as ABO. Even in ABO, if two ad sets are competing, budget fluctuations can occur in edge cases.
4. Manual Bidding or Bid Cap Settings
If you're using manual bidding (with highest volume or cost cap), the algorithm can occasionally overspend to win high-value impressions.
5. Glitch or Bug (yes, it happens)
Rare but possible — Meta's ad delivery system can experience overspend bugs. If it’s consistent or over multiple days, contact Meta support for a manual review and potential refund.
