GA4’s Conversion Paths report (under Advertising → Attribution → Conversion paths) shows how different channels contribute to conversions across the full customer journey — not just the last click. Most advertisers look only at last-click attribution, which systematically undervalues top-of-funnel channels like Organic Search, Display, and Social that initiate journeys completed through Paid Search or Direct. This guide explains how to read the Conversion Paths report, how to use it to challenge last-click attribution assumptions, and how to build a multi-touch path analysis in BigQuery for deeper insight.

How GA4 Attribution Models Work

GA4 supports several attribution models, accessible in the Conversion Paths report through the Attribution Model comparison selector. Last Click attributes 100% of conversion credit to the final touchpoint before conversion. First Click attributes 100% to the first touchpoint. Linear distributes credit equally across all touchpoints. Time Decay gives more credit to touchpoints closer to conversion. Position-Based (U-shaped) gives 40% to the first and last touchpoints and distributes the remaining 20% across middle touchpoints. Data-Driven uses machine learning to assign credit based on which touchpoints actually influence conversions in your property.

Data-Driven Attribution is GA4’s default model and is generally the most accurate when you have sufficient conversion volume (GA4 requires at least 400 conversions and 4,000 ad interactions per month to activate it). If your property does not meet this threshold, GA4 falls back to Last Click for Data-Driven model calculations.

Reading the Conversion Paths Report

The Conversion Paths report shows common paths as sequences of channel touchpoints. Each row represents a conversion path — for example, Organic Search → Paid Search → Direct. The report shows how many conversions followed that path and the total conversion value. The path visualization helps identify which channels typically initiate journeys (appear as first touchpoints) versus which close them (appear as last touchpoints).

Use the Attribution Model comparison dropdown to view how credit distribution changes across models. A channel that has low Last Click credit but high First Click or Linear credit is an assist-heavy channel — it drives users into the funnel but rarely closes conversions alone. This distinction is critical for budget allocation: cutting a high-assist channel based on last-click ROAS often reduces overall conversion volume because the top-of-funnel traffic it generates no longer enters the funnel for other channels to close.

Building Path Analysis in BigQuery

GA4’s Conversion Paths report is limited to 30 days of lookback and the channels GA4 defines. In BigQuery, you can build path analysis with any lookback window, custom channel definitions, and unlimited segmentation.

-- Build conversion paths from BigQuery GA4 data
WITH session_channels AS (
  SELECT
    user_pseudo_id,
    (SELECT value.int_value FROM UNNEST(event_params) WHERE key = 'ga_session_id') AS session_id,
    MIN(event_timestamp) AS session_start,
    MAX(IF(event_name = 'purchase', 1, 0)) AS converted,
    traffic_source.medium AS channel
  FROM `your_project.analytics_XXXXXX.events_*`
  WHERE _TABLE_SUFFIX BETWEEN '20240101' AND '20240131'
  GROUP BY user_pseudo_id, session_id, channel
),
user_paths AS (
  SELECT
    user_pseudo_id,
    MAX(IF(converted = 1, 1, 0)) AS did_convert,
    STRING_AGG(channel ORDER BY session_start SEPARATOR ' > ') AS path
  FROM session_channels
  GROUP BY user_pseudo_id
)
SELECT
  path,
  COUNT(*) AS users,
  COUNTIF(did_convert = 1) AS conversions,
  ROUND(COUNTIF(did_convert = 1) / COUNT(*) * 100, 1) AS conversion_rate
FROM user_paths
GROUP BY path
ORDER BY conversions DESC
LIMIT 50

Identifying Undervalued Channels

To quantify how much a channel assists conversions without getting last-click credit, compare its last-click conversion count to how many times it appears in any position of a converting path:

-- Channel assist vs. last-click ratio
SELECT
  channel,
  SUM(last_click_conversions) AS last_click,
  SUM(assisted_conversions) AS assisted,
  ROUND(SUM(assisted_conversions) / NULLIF(SUM(last_click_conversions), 0), 2) AS assist_ratio
FROM (
  SELECT
    last_channel AS channel,
    1 AS last_click_conversions,
    0 AS assisted_conversions
  FROM converting_paths_table
  UNION ALL
  SELECT
    assist_channel AS channel,
    0 AS last_click_conversions,
    1 AS assisted_conversions
  FROM assist_channels_table
)
GROUP BY channel
ORDER BY assist_ratio DESC

An assist ratio above 3 means a channel assists three times as many conversions as it closes. Channels with very high assist ratios (Organic Search, Display, YouTube) are systematically undervalued by last-click attribution models. Use this analysis to build the business case for maintaining investment in top-of-funnel channels that show low last-click ROAS but high path participation rates. Present this data alongside the last-click report to show the full contribution of each channel to conversion volume.