ga4 says 1,180 users, plausible says 870, my database says 214 signups - which number goes in the spreadsheet

Neither denominator, and that is not a dodge.

Browser analytics count sessions from browsers that allowed the script to run. GA4 loses people to ad blockers, to consent banners where nobody clicks accept, to ITP shortening cookie lifetime so the same human counts twice, and to bot filtering rules that differ between the two tools. Plausible loses a different set for different reasons. Neither one is measuring the population you care about, which is humans who could have signed up.

What I do: pick one tool as the trend instrument and never switch. Absolute value does not matter, direction does. Then compute the numbers that decide anything from your own database, server side, where you control the definition. Signups per day, activation per signup, paid per activation.

The rate you quote in your own head should be signups over one consistently-defined denominator, and you should write the definition down so future you cannot renegotiate it.

I built this exact spreadsheet three months ago and the thing that made it useful was cohorting by week rather than reporting a 30 day blob. A single number over 30 days hides that you changed the headline on day 11.

Weekly rows, one source per column, and a note column for what I shipped that week. It looks primitive next to a dashboard. It is the only analytics artifact I have ever gone back and reread.

Your specific gap has a boring explanation you can test in ten minutes. Developer-heavy audiences block trackers at a much higher rate than general consumer audiences, and the two tools handle bots differently. Look at whether your GA4 number includes traffic that Plausible classifies as automated.

Also check your GA4 data retention setting before you build any longitudinal report on it. On a standard property the event data retention drops back to the shorter option by default, and you can raise it to fourteen months in the admin section. People discover this when they try to compare against last year and find the data has aged out.

18 versus 25 percent is the wrong argument to be having, because both are suspiciously high for a landing page and that usually means the denominator includes people who came from somewhere warm. Split the traffic before you compute anything. Cold organic search converts nothing like a link you posted in a community where people already know you.

One blended conversion rate over mixed sources is a number that describes no real user and drives no real decision.

Also check what happens to your UTMs on redirect. Mine were being stripped by a redirect from the apex domain to www, so a chunk of paid and referral traffic was landing in direct. It made organic look better than it was and made a newsletter placement look like it did nothing, which nearly cost me a renewal on a placement that was actually working.

Instrument the funnel on your own side with four events and stop caring: page seen, form started, account created, first real action completed. Server side, in your own tables, one row each. Everything else is a nice-to-have.