Conversion window overlap
Conversion window overlap is what happens when multiple ad platforms each track their own click-to-conversion window for a buyer who touched several of them. A single sale can fall inside Google's window and Meta's window at once, so both count it. The overlap is structural, not a bug: walled gardens measure independently. Recognizing it explains why summed platform conversions exceed the real total and why de-duplication is required.
How overlap arises
Each platform defines a conversion window — the span after a click (or view) during which a conversion is credited to it. A buyer who clicked a Google ad and a Meta ad and then purchased sits inside both windows simultaneously.
Because walled gardens cannot see each other's touches, each independently and correctly (by its own rules) claims the same conversion. Their windows overlap on the shared buyer.
Why it inflates totals
Add up conversions reported by each platform and shared buyers get counted once per platform, so the sum overstates real conversions. The more channels a typical buyer touches, the worse the overlap.
There is no fix inside the walled gardens; resolution requires a neutral, de-duplicated source — your own first-party order data, a blended ratio, or unified measurement that reconciles claims against one ground-truth count.
- Each platform credits within its own conversion window
- Shared buyers fall inside multiple windows at once
- Summed platform conversions therefore exceed real sales
How it appears in analytics and logs
If total platform-claimed conversions exceed verified orders, overlapping conversion windows are double-counting buyers who touched multiple platforms.
Diagnostic use case
Explain why platform-reported conversions sum to more than actual sales, by showing how independent windows overlap on shared buyers.
What WebmasterID can help detect
WebmasterID's single first-party order count is overlap-free, giving a de-duplicated denominator to compare against summed platform claims.
Common mistakes
- Summing platform conversions as if windows were exclusive.
- Assuming a de-dup exists between separate walled gardens.
- Ignoring overlap when buyers touch many channels.
Privacy and accuracy notes
Windows operate on each platform's own aggregated conversion data; overlap is structural, not extra tracking. Educational, not legal advice.
Related pages
- Duplicate conversion counting
Duplicate conversion counting happens when a single real conversion is recorded more than once — for example by both a browser pixel and a server event, by a tag firing twice, or by two platforms each claiming it. It silently inflates reported conversions and value, distorts ROAS, and misleads bidding unless deduplication via shared event IDs and clear ownership is in place.
- Blended ROAS calculation
Blended ROAS is total revenue divided by total advertising spend across every channel, with no attribution model applied. Because platforms each claim overlapping conversions, summing platform-reported ROAS overstates performance; the blended ratio sidesteps that by working from one revenue figure and one spend figure. It is honest at the top line but cannot tell you which channel earned the return — that still needs attribution or incrementality.
- Lookback and conversion windows explained
A lookback (or conversion) window is the period before a conversion in which earlier touchpoints are eligible for credit. Touches outside the window are ignored entirely. Because every attribution model only sees touches inside this window, its length quietly governs which channels can ever receive credit.
- Attribution analytics
A single de-duplicated first-party order count.
Sources and verification notes
- Google Ads Help — About conversion windowsDefines per-platform conversion windows that can overlap.
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.