Conversion Lag
ConceptConversion lag is the time delay between an initial ad click and the final completed purchase, which makes recent-day campaign metrics provisional.
People rarely buy expensive items on their first click. If someone considers a mattress for 14 days before buying, the ad click happened on Day 1, but the conversion arrives on Day 14. If you check your ad dashboard on Day 2, the campaign looks like a failure because the sales are still in the pipeline.
An e-commerce brand spends $1,000 on ads today and logs $800 in immediate sales (0.8x ROAS). Over the next 7 days, returning shoppers complete their carts, pushing final revenue for today's spend to $3,200 (3.2x ROAS).
Panic-pausing campaigns after 24–48 hours because "ROAS looks bad" is a classic marketing mistake. Always allow for your average conversion lag before judging a campaign's true profitability.
Last reviewed August 28, 2026.