What is frequency capping, and why does it matter?
Limiting how many times the same person is shown the same advertisement within a period — and it matters because advertising effect does not rise indefinitely with repetition; it rises, plateaus, and then goes negative.
The underlying curve. The first few exposures do most of the work: establishing recognition and conveying the message. Additional exposures add progressively less — diminishing returns — and beyond a point produce wearout, where the audience becomes irritated and the advertising actively damages brand perception.
The practical consequence: money spent on the twentieth impression to the same person would have been worth far more reaching someone new.
Why over-frequency happens so easily in digital. Programmatic buying optimises toward people most likely to convert, and the people most likely to convert are those already engaged — so without a cap, the algorithm concentrates spend on a small, already-persuaded group. Retargeting is the worst offender, and the experience of being followed around the internet by a product you have already bought is the familiar result.
What a cap specifies: a number of impressions per user per time period — per day, per week, per campaign — and frequently a separate cap per creative.
The practical difficulties:
Cross-device and cross-platform, where the same person is counted as several. Capping within one platform does not prevent total over-exposure.
Identity loss. As tracking becomes harder, platforms cannot reliably recognise repeat users, so caps become less enforceable.
Walled gardens cap within themselves and cannot see each other.
Post-conversion suppression — excluding people who have already bought — is separate from frequency capping and is frequently neglected, which is why customers see acquisition advertising after purchasing.
What the right number is. There is no universal answer. Research in this area has generally supported a relatively low effective frequency for simple messages, with more required for complex or unfamiliar propositions. The measurable approach is to analyse conversion rate by exposure count and find where it flattens.
Reach versus frequency is the underlying trade-off: a fixed budget buys either more people or more repetition.