How do you know a backlink actually helped your rankings?

If you build links and update content in the same month, how do you tell which change made the difference?

What do you track to decide whether the backlinks were worth paying for? Would love to hear how you measure this on your own projects.

The cleanest way I have found is to stop changing two things at once. If you can, build links to a handful of pages and leave a few similar pages completely untouched, then compare both groups over the same weeks. Content updates go on pages that get no new links, and the other way around. Write down the date of every change, then look in Search Console at impressions and average position for those specific URLs and the queries they target, not the sitewide total. A real backlink effect usually shows as a slow climb on the target page a few weeks after the link gets crawled, while a content refresh tends to move things faster. If nothing changes after six to eight weeks, the link probably was not worth paying for.