Ad fatigue is the decline in ad performance that occurs when an audience has seen the same creative too many times. Attention and clickthrough fall, the platform compensates by charging higher CPMs, and cost per result climbs — the ad wore out, not the offer or the audience.
Every creative has a decay curve. The first impressions earn novelty attention; by the fifth or eighth exposure the brain files the ad as known furniture and scrolls past. Auction systems then make it worse: engagement-weighted delivery means a tired ad needs a higher CPM to win the same impression, so you pay more precisely when each impression is worth less.
Diagnosis is pattern recognition across four signals. Frequency: on Meta, trouble commonly begins around 3–4 average exposures for prospecting (retargeting tolerates more); climbing frequency on a stable audience means the pool is saturated. CTR trend: a creative that launched at 1.4% drifting to 0.7% over three weeks is the textbook curve. CPM/CPA trend: rising costs with unchanged targeting and competition. And Meta's first-time impression ratio — the share of impressions reaching new eyes — falling low confirms you're mostly re-showing.
Fixes in order of leverage: new creative (not a new color — a new concept, hook, or format; UGC vs studio, video vs static, different opening problem statement), broader or refreshed audiences (small retargeting pools and narrow interest stacks fatigue fastest), frequency caps where the objective allows, and rotation cadence — high-spend social accounts plan creative refresh every 2–4 weeks as routine maintenance, not as emergency response.
Don't over-diagnose: performance drops with stable frequency and falling first-time-impression ratios intact are usually competition or seasonality, and pausing a still-learning ad too early resets optimization. Confirm the exposure pattern before blaming fatigue.
DTC skincare prospecting ad set: week 1 — frequency 1.8, CTR 1.5%, CPA €24. Week 4 — frequency 4.6, CTR 0.6%, CPA €41, CPM up 35% on identical targeting. Launching two new concepts (a UGC testimonial and a before/after carousel) restores blended CPA to €26 within a week.
There's no magic number, but Meta prospecting commonly degrades from average frequency ~3–4 within a window; retargeting tolerates 6–10 because intent is higher. The trend matters more than the level: watch CTR and CPM move as frequency climbs.
Spend-dependent: high-budget social accounts refresh concepts every 2–4 weeks; smaller budgets stretch longer because audiences saturate slower. The reliable trigger is data — refresh when CTR decays 30–50% from launch on stable targeting.