How does the ad fatigue half-life work?
Borrowed from Nuclear physics: Exponential decay, half-life = ln 2 / λ
Physicists describe radioactive decay with a half-life, the time for half of a sample to decay. Creative fatigue follows a similar curve when audience size is limited: each exposure makes the next click a little less likely.
Enter the CTR on launch, the CTR now and the days between them. The tool fits the decay rate and projects when CTR reaches your refresh threshold.
Worked example
A US retailer launches an ad at 2.0% CTR, and after 10 days it reaches 1.4%. The decay rate is 0.036 per day, so the half-life is 19.4 days, and CTR falls to 70% of launch after 10 days, which is the usual refresh trigger.
How should I read my result?
The audience is small or frequency is high. Rotate three to four creatives and widen the audience.
Plan a new creative every three to four weeks, ready before CTR hits your threshold.
Fatigue is slow. Check frequency and refresh quarterly.
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Questions about ad fatigue half-life
What CTR drop should trigger a refresh?
A drop of 25 to 30 percent from launch is a common trigger. Test your own threshold.
Does fatigue always follow a smooth curve?
No. Real data is noisy, so use a week or more of data for each reading.
Can I extend the half-life?
Yes, by widening the audience, capping frequency or rotating several creatives.