In short
Click-through attribution credits conversions to ads that were clicked, within a defined window such as 7-day click. It is the strictest common standard, contrasted with view-through attribution, which credits conversions after an ad was merely seen. The window choice matters more than teams often expect, because a 1-day click window and a 7-day click window can report materially different performance for the same campaigns, and comparing two platforms on different windows produces misleading conclusions. The discipline is consistency: fix the window, apply it across the platforms being compared, and state it whenever the numbers are reported. Click-through is a conservative, defensible basis for attribution because it requires a deliberate action, but that conservatism has a cost, since it ignores the influence of impressions that shaped a decision without a click. Read it as the tight end of an attribution range, with view-through as the loose end, and judge campaigns against both rather than either alone.
Windows are settings, not truths
A 7-day click window and a 1-day click window report different conversion counts from identical campaigns. Neither is wrong; they are different questions. Comparing platforms on mismatched windows is the most common attribution reporting error.
Click-through versus view-through
Click-through requires a click; view-through counts users who saw an ad and converted without clicking. Most platforms report both, and honest cross-channel comparison keeps them separate.
How much does the attribution window change the numbers?
Two platforms report the same campaign very differently because one uses a 7-day click window and the other a 1-day window. Aligning the windows before comparing removes the artefact and shows the real difference in performance.
Reference: Google Ads Help, click-through vs view-through conversions