You log into Meta Ads Manager on a Monday morning, and last week's campaigns look solid. Then you switch to your attribution tool and the numbers tell a different story. That gap almost always comes down to the attribution window, a setting most e-commerce brands pick once during setup and never revisit.

A 7-day window and a 90-day window looking at the same brand will report wildly different revenue numbers. Understanding those differences is the only way to make confident decisions about where to put your budget.

An attribution window is the period of time after a customer interacts with an ad during which a resulting purchase gets credited to that ad. If someone clicks your Meta ad on Monday and buys on Wednesday, a 7-day click window will attribute that sale. If they buy 45 days later, only a longer window will catch it.

The shorter the window, the more conservative the count. The longer the window, the more conversions get pulled in. But longer windows also risk crediting sales that had nothing to do with the original ad click.

Here's what happens when you take a single month from one e-commerce brand and measure how much of their total revenue gets credited to ads across five attribution windows: 7 days, 14 days, 30 days, 60 days, and 90 days.

The brand: A DTC skincare company running Meta and Google Ads.

The month: January 2025.

Total store revenue: $245,000 across all channels (paid, organic, direct, email, everything).

Total ad spend: $52,400 across both channels ($34,100 on Meta, $18,300 on Google).

The store made $245,000 no matter what. The question is how much of that revenue each attribution window credits back to paid ads.

The store's total revenue for January was $245,000 across all channels. What changed across windows was how much of that $245,000 got credited back to paid ads. At a 7-day window, Meta and Google combined claimed $127,400 of that total (52%). At 30 days, that figure grew to $158,300 (65%). At 90 days, $174,400 (71%). The store didn't earn more money. The attribution window just decided how much of it paid ads could take credit for.

Meta defaults to a 7-day click, 1-day view attribution window. Google uses data-driven attribution with a default 30-day lookback. This means the two platforms are not reporting on the same basis.

When you compare Meta ROAS to Google ROAS in your weekly report, you're comparing numbers that are measured differently. Meta's 7-day click window is cutting off conversions that Google's 30-day window would happily count.

The only way to get a consistent, cross-channel view of attribution is to measure outside the platforms. The easiest way to do this is with an attribution tool that is built for e-commerce, like ThoughtMetric.

With ThoughtMetric, a single attribution window (7, 14, 30, 60, or 90 days) is applied across all marketing channels. ThoughtMetric connects to your Shopify or WooCommerce store, pulls in data from every ad platform, and applies consistent attribution models with adjustable windows across all channels. You see the real contribution of each channel without the platform-reported bias.

Book a demo to learn more about ThoughtMetric.