How Google Ads Tracks Sales Across Multiple Sessions: Conversion Windows Explained

One of the most persistent sources of confusion in Google Ads is the gap between what the platform reports and what actually happened. Google Ads shows 50 conversions, Shopify shows 30 orders and GA4 shows 38 transactions. All three are technically correct. They are simply measuring different things.

Understanding how Google Ads attributes conversions across sessions, devices and time is not just bookkeeping. It shapes how you judge performance, how Smart Bidding optimises, and which numbers you should actually trust.

How a Multi-Session Purchase Gets Credited

Most eCommerce purchases do not happen in one visit. A customer might:

• See a Shopping ad for your product, click, browse and leave
• Come back two days later through a Google search for your brand name
• Return three days after that by typing your URL and complete the purchase

Which of those visits gets credit for the sale?

Google Ads uses click-based attribution. When someone clicks an ad, a GCLID (Google Click Identifier) is stored in a browser cookie with a timestamp. When they later buy, conversion tracking reads that GCLID and attributes the sale to the click that created it.

In the example above, the Shopping click on day one gets credit for the purchase on day five, provided the purchase falls within the conversion window.

What the Conversion Window Is

The conversion window is the maximum number of days after a click during which a conversion is still credited to that click. You can set it separately for each conversion action.

Defaults:

• Click-through window: 30 days (adjustable from 1 to 90)
• View-through window: 1 day (adjustable from 1 to 30)

With a 30 day click-through window, a purchase made within 30 days of today’s click is credited to that click. A purchase on day 31 is not.

So a conversion you see in Google Ads today may come from a click up to 30 days earlier, which has big implications for reading performance over short date ranges.

Why Short Date Ranges Can Mislead You

This explains something many store owners notice. When you look at the last 7 days, the conversion count can include conversions credited to clicks from up to 37 days ago (the 7 days in range plus the 30 day window).

Google Ads distinguishes between reporting by click date and reporting by conversion date. Most standard reports use click date, crediting each conversion to the day of the click rather than the day of the purchase.

In practice, if last week’s campaign shows strong ROAS, some of those conversions are purchases made this week that were credited back to last week’s clicks. The data is not wrong. It shows click-date attribution, which is the right way to judge campaign efficiency.

To see conversions on the day they actually happened, use the conversion time columns (conversions by conversion time) instead of the default columns. That view is more useful for comparing with Shopify, which records each order on the day it was placed.

Why Google Ads and Shopify Disagree

When Google Ads shows more conversions than Shopify has orders for the same period, the cause is almost always one or more of these:

Cross-device purchases. Someone clicked your ad on their phone and bought on a laptop. Google uses their signed-in Google account to link the two devices and credits the ad click. Shopify records the order against the laptop session, so the order exists in both systems, but the source looks different depending on where you look.

View-through conversions. Someone saw a Display or YouTube ad without clicking and later bought. Google Ads counts this as a view-through conversion if it falls within the view-through window. Shopify knows nothing about the impression, so these add Google Ads conversions with no matching “Google Ads” session in Shopify.

Different date logic. As above, Google Ads defaults to click date while Shopify uses order date. A purchase on 1 January from a click on 25 December lands in December in Google Ads and January in Shopify.

Duplicate tracking. If both a Google Ads tag and an imported GA4 purchase goal send purchases to Google Ads, each order may be counted twice. Check Tools, Conversions: a GA4-imported purchase action alongside a separately tracked purchase action usually means duplication.

Other actions counted as conversions. Your Conversions column may include more than purchases (add to basket, checkout starts, newsletter sign-ups) if those are set as primary actions. Check exactly which actions feed the column.

Cancelled orders. Shopify records cancellations. Google Ads counts the purchase the moment it fires and does not remove it if the order is later cancelled, unless you upload conversion adjustments for refunds.

View-Through Conversions: Should You Trust Them?

A view-through conversion is recorded when someone sees an ad (Display, YouTube or Gmail), does not click, and buys within the view-through window.

They are the most debated conversions in Google Ads. Did the ad cause the purchase, or was the person going to buy anyway and simply saw an ad along the way?

Honestly, view-through conversions overstate advertising impact to some degree. Most people who see a Display ad while browsing would not buy because of it. A small share are nudged by the impression, with mild intent the ad reinforced. Crediting the full sale to an impression is generous.

When judging performance, separate view-through from click-through conversions by adding the “View-through conv.” column. If a large share of reported conversions are view-through, your click-through ROAS is lower than the blended figure suggests.

For direct response campaigns (Shopping and Search), leave view-through conversions out of your main ROAS calculation. For upper funnel campaigns (Demand Gen, Display prospecting) they are more relevant, but still deserve a cautious weighting.

Why Different Reports Show Different Numbers

Store owners often notice that conversion counts in the Campaigns view, the Keywords view and the attribution reports do not match. That is expected behaviour, not a data error.

Campaigns view and Keywords view: campaign conversions include everything credited to clicks from any keyword in that campaign, while keyword conversions cover clicks on that keyword specifically. They should broadly add up, but small differences appear because attribution models share partial credit across several touchpoints.

Last click and data-driven attribution: with data-driven attribution (the default for accounts with enough data), credit is spread across the touchpoints in a path. A keyword that was the third touchpoint might receive 0.4 of a conversion rather than a whole one. Campaign totals add up these fractions, which is why you see decimal conversion counts.

Search keywords and Shopping products: if you run both Search and Shopping, clicks from one customer’s journey can be credited across both, with the attribution model deciding the split. Do not expect them to add up to neat whole numbers.

Choosing the Right Conversion Window

The default 30 day click-through window suits most eCommerce stores, where buying decisions usually take days rather than weeks.

Shorter windows (7 days) suit impulse categories where customers buy straight after clicking or not at all. Fashion, low cost consumables and obvious impulse buys can benefit from a shorter window that filters out coincidental purchases.

Longer windows (60 to 90 days) suit considered purchases with lots of research: furniture, electronics, premium goods. If customers take weeks to decide, a 30 day window may miss purchases your ads genuinely influenced.

Check the path data in Google Ads (Tools, Attribution, Paths) to see how many days typically pass between first click and purchase in your account. If 90% of purchases happen within 7 days of the first click, a 30 day window adds noise without much benefit. If 20% happen between day 15 and day 30, the longer window is capturing real revenue.

The Most Reliable Way to Reconcile

If you need to reconcile Google Ads conversions with real orders:

• Switch Google Ads to conversion time reporting
• Remove view-through conversions
• Keep only click-based conversions
• Use the same date range in Google Ads and Shopify
• Accept that some gap will remain for structural reasons: cross-device attribution, different tracking systems and modelling always leave a difference

After those steps, a 10 to 20% gap is normal. A gap of 50% or more points to a tracking problem worth investigating, most likely duplicate tracking, a broken tag or a misconfigured conversion window.

The goal is not perfect reconciliation. It is tracking accurate enough to make confident bidding and budget decisions. Google Ads does not need to match Shopify order for order. It needs to be consistent, directionally right and stable enough for Smart Bidding to optimise towards real purchases.