Load Calc

I need to either replace my distribution box or add sub panel so that I can use arcfault breakers. (my current panel does not have these available). I am trying to decide if 100A is enough (and I won't need to change the entrance conductors) or if I should upgrade to 200A for future upgrades.
In particular, I have done the load calculation per NEC 220 and come up with 75A. I want to reserve enough extra current for a future spa. When doing a load calculation can I use all 100A rated on the panel or is there a derating factor I must use? How high in the load calc can one go before a larger service panel is indicated?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
In my opinion, if you are going to upgrade a panel the cost difference between a 100A and 200A is minimal compared to the cost of the labor. Go bigger, you may never need it but some future homeowner may appreciate it., I know I would.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.