Fluctuation of unique visitors, not of visits

Hi, what might be an explanation for having a lot of fluctuation in unique visitors per month, while the number of visits is growing rather smoothly?

Visitors (per month):

Visits (per month):

The fluctuation in visits can be explained with holiday times, but for unique visitors I don’t understand why the numbers differ so much from month to month. I don’t think this can be explained by random fluctuation as it’s to be expected for smaller sites, as my site has several hundred thousand visits per month.

Interesting. Did you look at the Engagement reports? It will tell you if you have a high number of returning visitors. If that’s the case it could explain what you are viewing.

According to Engagement → “Returning Visits Over Time”, about 60% of my visitors are returning visitors. I must admit I don’t understand how that could explain the numbers, could you explain?

BTW, in both daily and weekly view the unique visitors are aligned to visits and not fluctuating a lot. Here’s a weekly view:


Hi there,
The returning visits is telling us that your visitors are used to come back on your website, so when you have a huge drop of users in a monthly basis but still a high number of visits, it is giving us a clue that it is possible that data are right.
The other complimentary explanation is the following:
day 1: Luke is coming to your website, he is then register as a visitor.
day 2: Luke is coming back on your website.
day 3 to 7: Luke is always coming on your website.

Number of visitors on a daily basis: 1 visitor but appear as one dot per day
Number of visitors on a weekly basis: 1 visitor
Number of visitors on a monthly basis: 1 visitor

Hope it helps

I can’t be 100% sure yet, but this was maybe due to a misconfiguration. I had set the value Delete old visitor logs to 7 days. It even shows a warning: “When you enable automatic log deletion, you must ensure that all previous daily reports have been processed, so that no data is lost”. However, I had set that value long ago and I either ignored the warning or it wasn’t yet there in an old Piwik version. I’ve now increased that to 31 days and I’ll see if that helps.