Meta's default attribution model is last-click, meaning if someone clicks your ad and converts within the attribution window (typically 7 days for clicks, 1 day for views), that ad gets full credit for the conversion. This is the standard setup most advertisers see when they create campaigns in Ads Manager. But Meta also supports data-driven attribution (DDA), which uses machine learning to assign fractional credit to multiple touchpoints in a customer's journey. If someone saw your carousel ad, clicked a Stories ad two days later, then converted after clicking a feed ad, DDA tries to measure each interaction's actual contribution rather than giving everything to the final click. You enable this in your ad account settings under attribution, though it requires a minimum volume of conversions to function properly—usually a few hundred per month. The attribution window matters more than most people realize. Meta lets you choose windows like 1-day click, 7-day click, or 1-day view. Shorter windows undercount conversions but give you tighter control signal. Longer windows capture more conversions but can feel disconnected from what's actually driving results. For most e-commerce clients we work with, 7-day click / 1-day view is the sweet spot, but B2B or higher-ticket items often need custom analysis because the buyer journey stretches weeks. One major shift: iOS 14.5+ and ATT (App Tracking Transparency) broke a lot of Meta's attribution accuracy. Aggregated Event Measurement now limits you to eight conversion events per domain, and if users opt out of tracking, Meta loses visibility into their full path. This means your reported conversions in Ads Manager are often 20-40% lower than what Google Analytics or your actual sales data shows. At Ottawa SEO, we always cross-reference Meta's attribution against GA4 and server logs. Meta's numbers are directionally useful for optimization, but if you're making budget decisions or calculating true ROAS, you need to layer in your own conversion tracking and accept that attribution is messy across all platforms now.