Budget
Cost Cap vs Bid Cap -- Which Should I Use?
Manual bidding is frequently recommended as a solution to high CPA. It is often the cause of new problems. Understanding when it applies and when to leave it alone prevents most manual bidding mistakes.
What is actually happening
Lowest Cost (no manual bid): Meta bids whatever it needs to win impressions and optimise toward your conversion event. Delivery is unconstrained by CPA targets. Best used when you are in the learning phase or do not have a known CPA target. Cost Cap: tells Meta to maintain an average CPA at or below your cap across the campaign. Meta will sometimes bid above the cap to win specific auctions but averages down over time. Requires a known CPA target based on historical data -- setting it without data produces either no delivery (cap too low to win auctions) or no meaningful constraint (cap too high). Bid Cap: hard ceiling on each individual auction bid. More restrictive than Cost Cap. Often causes severely limited delivery -- Meta cannot win enough auctions to deliver at meaningful volume. Use only for very specific budget efficiency requirements with proven performance data.
⚑ Most common wrong move
Using Bid Cap or Cost Cap without historical CPA data to set them. A Cost Cap set to €10 on a product that actually costs €25 to acquire will produce no delivery. The campaign wins no auctions. Most 'Meta ads don't work' experiences in the first 30 days are actually 'manually set bid caps that prevented delivery.'
What to do
1Start every new campaign with Lowest Cost bid strategy. This allows Meta to find the real market CPA without artificial constraints.
2After 50+ conversions over 14+ days: calculate your average CPA from Lowest Cost. That number is your real market CPA.
3Only then consider Cost Cap: set it at 10-20% above your observed CPA to allow delivery flexibility while capping spend efficiency.
4Avoid Bid Cap entirely unless you have a specific auction-level CPA requirement (performance marketing with hard unit economics constraints at scale).
5If delivery drops after enabling Cost Cap: your cap is below market clearing price. Raise it by 20% and reassess after 3 days.
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