Why week 0 is not 100% for "new users" event?

  • 14 February 2022
  • 4 replies


Hi there!


I am a little confused with the retention chart and some of the numbers in it. I've created a simple retention chart with start event being "New User" and return event event being "Any Active Event". So far so good. The first thing I notice that seems odd is that the week 0 of the line chart is not 100%. Furthermore, when I look at the breakdown table, the most recent cohorts have a set number of total users but the week 0 percentage is not 100%. I am mostly confused because I thought week 0 would just account for the start event ("New User") and always be 100%. I was able to replicate it in the demo env:

Maybe I am a bit confused with the New User event and not using it properly. I appreciate the help!




João da Matta




Best answer by SheenaGreen 14 February 2022, 20:24

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4 replies

Userlevel 4
Badge +8

Do you have a lot of events marked as inactive? When I switch the demo set up to “Any Event”, the value for week 0 goes to 100%. We only have a few events marked inactive in our set up, so when I use our data and set the returning event as “Any Active Event”, week 0 is at 99%. I imagine if you have a lot of events marked inactive, but Amplitude is still ingesting them, this would cause the issue you’re seeing. 


Thanks for the reply!

I have 0 events marked as inactive. If I understand correctly what you said, the percentage for week 0 for a specific cohort will be:

(# of user who performed the return event on week 0) / (# of new users)

Is that right? If so, it makes sense for the % on week 0 to not be 100%.

Userlevel 7
Badge +10

Hey @jdamatta 

I agree with Sheena here.

On looking at the demo chart and dropped off users for Week 1, it looks like the return event (and the only event) for some of them in Week 0 is the “[Experiment] Assignment” event. This event is marked as inactive in the AmpliTunes Demo chart, which is why the chart with return event as “Any Active Event” is showing <100% retention for Week 0.


Userlevel 4
Badge +7

Hey there,

thanks for writing in! I completely understand why you have this confusion, and would love to explain to you why the "Week 0" retention values might be less than 100%. 

The first thing to know is that it is possible that the 'Week 0' or 'Day 0' retention rate is not 100%. Amplitude considers users to be retained when they fire both the starting event and returning event in the specified time range. So the chart might not show a 100% retention rate in 'Week 0' because not all users fired both A event (starting event) and B event (returning event) in the time period you selected. The 32.7% retention rate in 'Week 0' means among all the users who fired the starting event (e.g Became New users), 32.7% of them came back and fired the returning event within a week.  

Here is a very useful article from our help center in case you would like to learn more about the Retention chart.

Hope it clarifies!