Google's rule says at least 12 testers, opted in continuously for 14 days. If you recruit exactly 12, one dropout puts you under the line. So how many should you recruit? We can give you a rule of thumb from real records. Google's rule is in its testing requirements.

The data behind it

In ClosedTest's completed runs (1,495 tester assignments, as of 26 October 2026), 80.1% of assignments had a check-in on at least 10 of the 14 days, and 41.6% checked in on all 14 days. The full breakdown is in what 1,495 tester assignments show.

Two cautions. These are managed, paid testers with daily reminders, so volunteers may do worse. And a check-in is our measure of engagement, not Google's opt-in status. Treat the result as a starting point.

The rule of thumb

If about 80% of testers stay engaged, then to end with 12 engaged testers you need:

12 ÷ 0.80 = 15 testers, as a minimum.

Testers you recruit	Expected to stay engaged (about 80%)
12	9.6
14	11.2
15	12.0
16	12.8
18	14.4
20	16.0

Averages hide bad luck. A single test can lose more people than the average. So treat 15 as the bottom of the range and add a margin: 16 to 20 testers is a safer plan.

What about Google's own count?

Google counts testers who are opted in, not testers who checked in. A tester can stay opted in and still be silent. Both matter: opt-in keeps you above 12 for Google's rule, and engagement is what you describe on the form and what Google names as a reason to keep testing. See what to do when Google asks for more testing.

What this means for choosing a plan

If you run your own test, recruit 16 or more. If you use a service, check how many testers the plan includes above 12.

At ClosedTest, the Minimum plan has 12 testers and no buffer. Our data suggests that leaves little margin. The Safe Buffer plan (16 testers) and the Maximum plan (20) add testers above 12. See the pricing. If you choose Minimum, we replace testers who drop out, but a late replacement still needs time. See the 12-tester rule explained.

You can check your own numbers with the free 12 tester calculator.

ClosedTest is an independent service and is not affiliated with Google.