Attribution & Conversion Counting

Last-Click Attribution vs Time-Decay Attribution

In short: Both models weight touches by how close they sit to the conversion, but last-click takes that logic to its extreme while time-decay spreads it across the whole path. Last-click gives 100 percent to the final touch and zero to everything before it. Time-decay gives partial credit to every touch, but shrinks that credit the further back in time it happened, typically on a roughly weekly half-life. Last-click is still selectable in Google Ads; time-decay was dropped from Google Ads and GA4 reporting in 2023. If your sales cycle is short, the two will barely disagree; if it is long, pick time-decay when you want to acknowledge early touches without pretending they mattered as much as the final one.

By the AdFlint research team · Fact-checked against current Google and Meta platform behavior · Last reviewed July 2026

Last-Click Attribution

Gives all conversion credit to the final ad click before the conversion, ignoring every earlier touchpoint in the path.

All credit lands on the final click before the conversion, which makes reporting simple and reproducible but flattens upper-funnel work. Advertisers use it when paths are short or when they need an auditable baseline everyone can recompute. Google Ads still offers it while defaulting to data-driven attribution. The usual mistake is reading last click as what the ad caused rather than simply where the path ended.

Full definition

Time-Decay Attribution

Weights touchpoints by recency, so interactions closer to the conversion receive exponentially more credit than ones earlier in the path.

Credit decays on a half-life, commonly seven days, so a touch a week before the conversion carries half the weight of one on the closing day. It suits long consideration cycles where recent activity signals intent. Google Ads and GA4 dropped it from reporting in 2023. The misunderstanding is assuming the half-life is tuned to your business; it is a fixed default, not something the model learns from your data.

Full definition

Side by side.

The differences that actually change what happens in your account.

	Last-Click Attribution	Time-Decay Attribution
What gets credited	Only the final click - 100 percent or nothing.	Every touch, weighted more heavily the closer it sits to the conversion date.
How it treats an old touch	Ignores it completely, however relevant it was.	Gives it a small, non-zero credit that fades on a fixed schedule.
Tunable to your business	Nothing to tune - it is a fixed rule.	Not really; the decay half-life is a platform default, not something learned from your data.
Availability today	Still selectable inside Google Ads.	Removed as a selectable model from Google Ads and GA4 in 2023.
Best suited to	Short paths, single-session purchases, impulse buys.	Longer consideration cycles where several touches happen over days or weeks before conversion.
Data requirement	Just the final click, already captured by standard conversion tracking.	A full timestamped path export, since neither platform computes it anymore.
Failure mode	Erases a genuinely influential early touch entirely.	Applies a decay curve that has nothing to do with how your specific customers actually decide.

What actually separates them.

Last-click is a binary rule - one touch gets everything - while time-decay is a continuous curve, so time-decay can express that a touch mattered a little in a way last-click structurally cannot.

Time-decay's weighting depends on elapsed time between touch and conversion, meaning the exact same click can be worth more or less credit depending on how quickly the customer converted afterward; last-click's credit never depends on timing at all, only on click order.

Last-click remains a live, selectable option inside Google Ads; time-decay requires reconstructing the path from exported data since it is no longer computed by either Google Ads or GA4.

Because time-decay's half-life is a fixed platform default rather than something calibrated to your sales cycle, a business with a six-month cycle and one with a six-day cycle would see the same decay curve applied, which can misrepresent both.

A campaign that only ever shows up early in the path gets zero recognition under last-click but a small, real share under time-decay, so switching between the two models can materially change which campaigns look worth keeping.

Which one should you use?

Use Last-Click Attribution when

Your typical customer converts in a single session or within a day or two of first contact.
You want a number Google Ads already computes, with no export or extra math.
You are feeding a bid strategy built around the platform's own conversion counting.
You need a simple, auditable baseline that does not require explaining a decay curve to stakeholders.

Use Time-Decay Attribution when

Your sales cycle regularly runs days to weeks, with multiple touches before someone converts.
You want early touches to register as somewhat influential without letting them outweigh the touch that actually closed things.
You have the multi-touch data to reconstruct it, since neither Google Ads nor GA4 offers it natively anymore.
You are comparing it against last-click specifically to see how much upper-funnel credit last-click is silently discarding.

Common questions.

What's the actual decay rate in time-decay attribution?

Most implementations use a roughly seven-day half-life as a default, meaning a touch a week before conversion is worth about half what a touch on the conversion day is worth. That half-life is a fixed convention baked into the model, not something the platform calibrates to your specific sales cycle, so treat it as a rough shape rather than a precise measurement.

Can I still run time-decay attribution in Google Ads or GA4?

No, both platforms removed it as a selectable model in 2023 along with the other rule-based comparison models, leaving data-driven attribution as the default. To see a time-decay view now you would need to export timestamped conversion paths and apply the decay calculation outside the platform.

Is time-decay just a smoother version of last-click?

In a sense, yes - as the half-life shortens, time-decay's output converges toward looking like last-click, since older touches get squeezed toward zero credit. The difference is that time-decay never fully zeroes out an early touch the way last-click does, it just makes it small.

Why would I use time-decay instead of position-based for a long sales cycle?

Position-based fixes the first and last touch at 40 percent each regardless of timing, while time-decay lets the actual gaps between touches drive the weighting, so it fits better when you care about recency specifically rather than just rewarding the bookend moments of the journey.

Or stop choosing between them.

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