What's GA4's Default Attribution Lookback Window?

GA4's default attribution lookback window is 30 days for acquisition events — specifically first_open and first_visit — and 90 days for every other conversion event. Both can be changed in the property's Attribution Settings, and as of an August 2026 update, Google replaced the old preset dropdown with custom integer values instead of a fixed list of options.

The Two Default Windows

• Acquisition events (first_open, first_visit) — default to a 30-day lookback, with 7 days available as the alternative preset-era option for businesses with a much shorter path from first touch to acquisition.
• All other key events — default to a 90-day lookback, covering purchases, leads, sign-ups, and any other conversion event configured outside the acquisition category.

What Changed in August 2026

On August 11, 2026, Google removed GA4's fixed preset list for lookback windows and replaced it with free-entry integer values. Click-through conversions, which previously only offered 1, 7, 14, 30, 60 or 90-day presets, now accept any whole number of days from 1 to 90. Engaged-view conversions, previously fixed at a flat 3 days, now accept any integer from 1 to 30. Properties that hadn't touched their attribution settings kept their existing preset value as the starting point after the change, rather than being reset.

Why the Lookback Window Applies to Session Attribution Too

The key-event lookback window a property chooses doesn't only affect conversion counting — it also governs session attribution, meaning the window determines how far back GA4 will look to credit a session, and therefore a channel or campaign, with a given conversion. A shorter window attributes more conversions to whichever touchpoint happened most recently, while a longer window spreads credit further back toward earlier-funnel channels.

When to Shorten or Lengthen It

A business with an impulse-purchase sales cycle — same-day or next-day converters — gets a more accurate attribution picture from a shorter window, since a 90-day default would let GA4 credit touchpoints from months-old sessions that had little real influence on the eventual conversion. A longer sales cycle, like B2B software or high-ticket purchases researched over weeks, benefits from extending the window closer to the full 90-day maximum for click-through conversions so earlier research-stage touchpoints aren't undercounted.

This Is a Separate Setting From Google Ads' Own Attribution Window

GA4's lookback window governs how GA4 itself attributes conversions in its reports; it's a distinct setting from the conversion window configured inside Google Ads, which controls how Google Ads attributes and reports conversions for bidding and billing. A property can have GA4 and Google Ads linked and still run different lookback windows in each tool, so checking one doesn't tell you what the other is set to — they have to be checked and aligned separately if consistent attribution across both is the goal.

Bottom Line

Check your GA4 property's Attribution Settings against your actual average time-to-conversion rather than assuming the 30/90-day defaults fit your business, and take advantage of the August 2026 move to custom integer windows to match the setting to your real sales cycle instead of the nearest preset.

Source: Google Analytics Help, "Advertising and attribution" (support.google.com/analytics/answer/10597962); Google Analytics Admin API, AttributionSettings reference (developers.google.com/analytics/devguides/config/admin/v1/rest/v1alpha/AttributionSettings).