I'm new to futures and I'm trying to understand how margin is calculated when it comes to VIX. For the sake of example, let's say VIX is 20 today and 60 day VIX futures are selling for 25. So far, this makes sense to me: if you're going to be short VIX, you want some margin of safety, so that's why it's 25 and not 20. Say I buy a 60 day VIX futures contract (which currently trades at 25). Based on what I read, required margin is calculated at the end of every trading day. But what is used for the basis of that calculation: the spot VIX price of 20 or the 60 day VIX futures price of 25. Because if it's the former, then I'm out of $5000 the very first day I bought the 60 day VIX futures contract for 25. (I think VIX futures use a $1000 multiplier per point). Is this correct?
if you're going to be short VIX, you want some margin of safety, so that's why it's 25 and not 20
No, that means that the market thinks that the VIX will be at 25 in 60 days. It has nothing to do with "margin of safety". You could make the opposite argument if you're long VIX.
The required margin for your futures position will be based on the futures value, not the spot value.