Google Ads Conversion Windows: The Setting That's Quietly Inflating Your E-Commerce ROAS

If your Google Ads dashboard says you're getting an 8x return but your bank account, your Shopify revenue and your gut all disagree, this article explains why. The culprit is usually a setting most advertisers have never opened: the conversion window. It takes five minutes to check, and if it's been stretched, every performance number you've been shown is inflated.

What Is a Conversion Window?

Every conversion action in Google Ads (a purchase, a lead, a sign-up) has a conversion window, the period of time after someone interacts with your ad during which their purchase still gets credited back to that ad.

Simple example: a customer clicks your ad on the 1st of the month and buys on the 20th. With a 30-day click-through window, Google Ads counts that sale as an ad conversion. With a 14-day window, it doesn't. Same customer, same sale, same ad, the only thing that changed is a setting. That setting silently defines what "performance" means in your account, and almost nobody audits it.

There are actually three separate windows per conversion action, and each one credits sales on progressively weaker evidence:

• Click-through window (1-90 days available), credit after someone clicks an ad. The strongest signal of intent: they saw your ad and actively chose to visit.
• Engaged-view window (1-30 days), credit after someone watches 10+ seconds of a video ad without clicking. They never visited your site from the ad; Google infers the ad influenced them.
• View-through window (1-30 days), credit after someone merely had an ad impression rendered on their screen. No click, no watch. They may not have consciously noticed the ad at all.

The further down that list you go, the more the "conversion" is a statistical guess rather than a measured cause. Stretch those windows and the guesses pile up fast.

What We're Seeing in the Wild

Across the e-commerce accounts we audit, particularly agency-managed ones, a pattern keeps showing up:

• 60-90 day click-through conversion windows
• 14-30 day engaged-view windows
• 7-14 day view-through conversion windows

For a typical e-commerce brand, the genuine purchase consideration cycle is 1-14 days. Nobody deliberates for three months over a £40 product. So what do these stretched settings actually do?

• Stale clicks get credited. A customer clicks an ad in January, forgets about you, then comes back in March through your email newsletter and buys. With a 90-day click window still open, Google Ads claims that sale, even though your email did the work.
• Other channels get cannibalised on paper. Sales genuinely driven by email, organic search, social, influencers or people simply typing your URL get attributed to Google Ads because an ad click or impression existed somewhere in the trailing window. Irrelevant data flows into the account and gets dressed up as ad performance.
• View-through is the worst offender. Someone scrolled past a display banner ten days ago, then searched your brand name and bought organically. Google Ads books the revenue. No click ever happened. On long view-through windows this isn't measurement, it's revenue laundering between channels.
• Repeat customers inflate it further. Brands with loyal customers are hit hardest: every returning buyer who clicked any ad in the past 90 days gets re-credited to ads, even when retention channels drove the repeat purchase.
• ROAS and sales figures inside Google Ads climb well beyond what the channel actually drove. The dashboard looks brilliant. The P&L doesn't move.

A Worked Example: How Big Is the Inflation?

Say you spend £10,000/month and Google Ads reports £80,000 in conversion value, a reported 8.0x ROAS. But the account runs a 90-day click window with 14-day view-through, and when you cross-check independently you find:

• £12,000 of that "ad revenue" came from view-through conversions, impressions, not clicks;
• £14,000 came from clicks older than 30 days, where email or organic closed the sale;
• leaving roughly £54,000 genuinely attributable to ads in a realistic window.

Your real ROAS is 5.4x, not 8.0x, a 48% overstatement. Every decision built on the 8x is wrong: the budget you scaled, the products you doubled down on, and the performance fee you paid on it. (For context on what honest ROAS figures look like at different spend levels, see what is a good ROAS for Google Ads.)

Why Smart Bidding Makes It Worse, Not Better

This isn't just a reporting problem. Google's automated bidding (Target ROAS, Maximise Conversion Value) optimises toward whatever the conversion column says. Feed it conversions that email and organic actually drove, and Smart Bidding learns to bid on people who were going to buy anyway, your existing customers and brand searchers, because those "convert" most reliably inside a long window. The algorithm looks smarter, the reported ROAS climbs further, and your actual incremental revenue per pound of ad spend quietly falls. It's a self-reinforcing loop, and the longer the window, the tighter the loop.

How to Check Your Conversion Windows in Google Ads

You don't need edit access or any technical skill, read-only access is enough. Five minutes:

1. Sign in to Google Ads at the account level (if you're in an agency MCC view, make sure you're inside your account).
2. Click the Goals icon in the left-hand navigation.
3. Go to Conversions → Summary.
4. Click into your main purchase conversion action (usually named "Purchase" or similar).
5. Open Edit settings, you can view the values without saving anything.
6. Read three fields: Click-through conversion window, Engaged-view conversion window and View-through conversion window. Write them down.
7. Repeat for every conversion action marked Primary, primary actions feed Smart Bidding and the headline "Conversions" column. (Secondary actions are observation-only.)
8. While you're there, note the attribution model and check which column your reports are built on: in any campaign view, Columns → Modify columns → Conversions. "Conversions", "All conv." and "View-through conv." are different columns measuring different things, if your agency reports "All conv. value", ask why.

The rule for e-commerce: 30-day click-through window · 7-day engaged-view window · 1-day view-through window. Anything beyond that needs a written commercial justification, and "more data for the algorithm" is not one.

How to Build a GA4 Explore to Cross-Reference Reality

Google Ads marks its own homework. Google Analytics 4 measures the same purchases through an independent, cross-channel lens, which makes it the cheapest referee you have. Build the comparison view once and reuse it every month:

1. Open GA4 and click Explore in the left navigation.
2. Create a Blank exploration and name it (e.g. "Channel Revenue Cross-Check").
3. Set the date range to exactly match the Google Ads period you're auditing. Misaligned dates invalidate the whole comparison, so be precise.
4. Under Dimensions, click + and import: Session default channel group, Session source / medium and Session campaign.
5. Under Metrics, click + and import: Purchases (key events), Total revenue (or Purchase revenue) and Sessions.
6. Drag Session default channel group into Rows.
7. Drag Purchases and Total revenue into Values.
8. You now see where revenue is actually coming from: Paid Search, Organic, Email, Direct, Paid Social, Referral, side by side.
9. Add a second tab (or swap the row dimension) using Session source / medium to isolate google / cpc, that line is what Google Ads paid traffic genuinely closed.
10. Recommended: add a filter Session source / medium exactly matches google / cpc and break rows out by Session campaign to compare campaign-level revenue directly against the Google Ads UI.
11. Now put the two numbers next to each other: Google Ads reported conversion value vs GA4 revenue attributed to google/cpc for the identical period.

Fair-comparison notes: GA4 and Google Ads will never match to the penny, GA4 is session-scoped and cross-channel, Ads is interaction-scoped and windowed; consent banners, ad blockers and conversion lag all create a small natural gap. Exclude the most recent 3-7 days from the comparison (conversions are still being reported into that period) and compare a full clean month where possible. The deviation rule below already accounts for the honest portion of the gap.

The 3-5% Deviation Rule

With the same clean date window in both platforms, apply this test:

• Within 3-5% deviation: attribution is healthy. Google Ads is claiming roughly what it genuinely drove.
• Beyond 3-5% deviation: Google Ads is boosting its own figures off the back of extended conversion windows, claiming revenue that belongs to email, organic, social or direct. Your "ROAS" is partly other channels' work wearing a Google Ads badge.

And here's the part that matters commercially: if your agency manages the account on a percentage-of-spend or percentage-of-revenue model and the windows are stretched to 90/30/14, they are either lying to you or committing fraud. Inflated attribution directly inflates their reported performance and, on a revenue-share model, their invoice. At best it's negligence; at worst it's deliberate misrepresentation of results for financial gain. Either way, the deviation check gives you the evidence in black and white: their platform screenshot vs your independent GA4 data. You don't need to argue, you just need to show both numbers. (This sits alongside the other marketing agency red flags worth checking before you sign or renew.)

What To Do If You Find It

1. Screenshot the current window settings before anything changes. Settings can be quietly "fixed" once questions get asked, date-stamped screenshots are your paper trail.
2. Reset the windows to the e-commerce rule: 30-day click-through, 7-day engaged-view, 1-day view-through.
3. Expect reported ROAS to drop after the change, and hold your nerve. Performance didn't get worse; it got honest. Historical conversions keep their original window, so the numbers wash through over the following weeks. Re-baseline your targets on the honest figures.
4. Give Smart Bidding 2-4 weeks to relearn on clean conversion data before judging campaign performance. Bids were trained on inflated signals; they need time to recalibrate.
5. Re-run the GA4 cross-check after 30 days. The deviation should collapse into the 3-5% band. If it doesn't, keep digging, check for double-counted conversion actions and imported GA4 key events sitting alongside the Ads tag (both marked primary = every sale counted twice).
6. If an agency set this up and billed against the inflated numbers, ask them in writing to justify the window settings. Their answer will tell you everything you need to know about the relationship.

Attribution settings aren't admin. They're the difference between scaling what genuinely works and funding a spreadsheet illusion, and they take five minutes to check. It's one of the first things we look at in every free PPC audit, and honest attribution is the foundation of our Google Ads management service.

Frequently Asked Questions

What conversion window should e-commerce brands use in Google Ads?

For e-commerce, the rule is a 30-day click-through window, a 7-day engaged-view window and a 1-day view-through window. Anything longer needs a written commercial justification tied to your actual purchase cycle.

Won't a shorter conversion window lose conversions?

No sales disappear, customers still buy. What changes is which channel gets the credit. A 30-day click window captures the overwhelming majority of genuine ad-driven e-commerce purchases; what it stops capturing is revenue that email, organic and direct actually drove. If a meaningful share of your real ad conversions took 60+ days, you'd sell considered high-ticket purchases, and you'd know it from your own sales cycle.

Why doesn't GA4 match Google Ads conversion data?

They measure differently by design: GA4 is session-scoped and cross-channel, Google Ads is interaction-scoped and windowed. A small stable gap is normal measurement noise. A 20-40% gap that widens as conversion windows get longer is attribution inflation, and it moves exactly in line with the window settings.

How do I check if Google Ads is over-reporting my ROAS?

Compare Google Ads conversion value against GA4 revenue attributed to google/cpc for the same clean date range, excluding the most recent 3-7 days for conversion lag. If the figures deviate by more than 3-5%, Google Ads is boosting its figures off the back of extended conversion windows.