Numpty >>
sunday july 17 - 18:04, Edited
tuesday july 19 - 09:39 Depends on your likely attendances @pii. And also the size of the remaining bank balance after upgrading.
If you want to have a forum search I looked at the detail of this in a thread a long while ago before starting mine.
There are 2 aspects to consider, the loss of interest that you mention and also the higher maintenance costs. From memory you need to average 120,000 just to break even on the extra maintenance costs. After that you're in profit but will need a lot more than the 120,000 to account for the loss of interest.
If your balance falls to near zero after paying the construction costs then you'll obviously need much better attendances than if your balance is a lot higher. You'll also lose a lot of interest during the 2 seasons that it takes to build.
As far as I can recall I think I waited until my balance was near $1.5 billion before pressing the build button in order to mitigate some of the lost interest.
Edit
A bit more specific detail in my post dated 05 May 2020, here:
https://rockingsoccer.com/en/soccer/forum/home-en/392?topic=25070