Time Decay Attribution
Time decay attribution is a multi-touch attribution model that gives more conversion credit to touchpoints that happen closer in time to the conversion. A touch that occurs minutes before a purchase earns far more credit than one from three weeks earlier. It exists to reward the channels that push a buyer over the line while still acknowledging the earlier touches that started the journey.
How Time Decay Attribution Works
Time decay weights credit using an exponential decay curve based on each touchpoint’s distance from the conversion. The closer a touch is to the sale, the larger its share.
The curve is controlled by a half-life. A half-life is the gap at which a touchpoint earns half the credit of one at conversion time. Google’s default half-life was 7 days. So a touch 7 days before the sale gets 50% of the credit a touch at conversion gets. At 14 days, it drops to 25%.
This makes time decay one of the more nuanced multi-touch attribution models. It never ignores a touchpoint completely. It simply trusts recent interactions more than old ones.
Time Decay Attribution Example
Consider a customer who buys a $400 product after four interactions over two weeks:
- Clicks a Google Ad 14 days before converting
- Reads an organic blog post 7 days before
- Opens a marketing email 1 day before
- Returns through a direct visit and converts
With a 7-day half-life, the touches closest to the sale carry the most weight. The direct visit and email might together take around 65% of the credit. The blog post earns a moderate share. The Google Ad from two weeks back receives the smallest slice, perhaps 8%.
Compare that to linear attribution, which would split the $400 evenly at $100 each. Time decay instead pushes most of the revenue toward the final touches that closed the sale.
When to Use Time Decay Attribution
Time decay suits sales cycles where recent touchpoints genuinely do the heavy lifting. It fits a few cases well.
- Short or promotion-driven cycles, where late-funnel nudges like retargeting and email drive the conversion.
- Bottom-funnel optimization, when you want to reward the channels that close rather than the ones that introduce.
- Considered purchases with a clear closing phase, where the final week of activity matters more than the first impression.
It is a weak fit for brand-awareness measurement. Time decay systematically undervalues the first touch that created demand. If top-of-funnel content is your priority, first-touch or position-based models give a fairer picture.
Time Decay vs Other Attribution Models
Time decay sits between simple single-touch models and fully data-driven ones. It applies a rule, but a smarter rule than equal splitting.
| Model | Credit split |
|---|---|
| First-click | 100% to the first touch |
| Last-click | 100% to the last touch |
| Linear | Equal share to every touch |
| Time decay | More credit to touches closer to conversion |
| Position-based (U-shaped) | 40% first, 40% last, 20% to the middle |
| Data-driven | Credit by each touch’s measured contribution |
The trade-off is recency bias versus simplicity. Time decay is more realistic than linear for closing-heavy funnels. But it assumes recent always means more important, which is not true for every business.
Platform Support for Time Decay Attribution
Time decay is no longer selectable in Google’s main tools. Google removed first-click, linear, time-decay, and position-based models from Google Analytics 4 and Google Ads in 2023, leaving only data-driven and last-click. Google stated that data-driven attribution had made the rule-based models redundant.
You can still apply time decay in CRMs, BI dashboards, marketing mix tools, and spreadsheets where you set the half-life yourself. Accurate weighting depends on clean touchpoint data, which starts with consistent UTM tags on every campaign link so each interaction is timed and recorded correctly.
Frequently Asked Questions
What is time decay attribution in simple terms?
Time decay attribution gives more conversion credit to touchpoints that happen closer to the sale. The last few interactions earn the largest share, while older touches earn less. It assumes recent touchpoints did more to close the deal, without ignoring the earlier ones entirely.
What is an example of the time decay model?
If a customer clicks a Google Ad two weeks out, reads a blog a week out, opens an email a day before, then converts, time decay credits the email and conversion-day touches most. The Google Ad earns the smallest slice. A $400 sale would skew most of the revenue to the final touches.
What is the half-life in time decay attribution?
The half-life is the time gap at which a touchpoint earns half the credit of one at conversion. Google’s default was 7 days. A touch 7 days before the sale gets 50% of the weight, and a touch 14 days out gets 25%. A shorter half-life concentrates credit on the most recent touches.
Does GA4 still support time decay attribution?
No, GA4 removed time decay, first-click, linear, and position-based attribution in 2023. Only data-driven and last-click (cross-channel) models remain selectable. You can still calculate time decay manually or in tools outside Google’s ecosystem.
To choose the right model for your funnel, read linkutm’s campaign attribution guide, which walks through all six models and their trade-offs.