Tesla doesn’t not publish monthly sales figures, but rather reports deliveries on a quarterly basis. So, InsideEVs uses their own method to estimate deliveries:
We never know for sure what the monthly numbers total up to until Tesla’s quarterly (or annual) updates add more clarity. However, we do our best to keep our finger on the pulse of what’s happening.
To come to an estimated monthly number, we don’t simply take the quarterly estimate given by Tesla and divide it by 3 and hope it all works out. This is surely not how it works in the real world. We simply report from the data we accumulate ourselves, including first-hand accounts available from the factory and from the community itself.
Historically, while InsideEVs hasn’t been exact on monthly Tesla deliveries in the past, their estimates have been generally in the ballpark and provide useful information.
Most notable, InsideEVs estimates that Tesla has delivered 1,875 Model 3s in January.