Returns of an interest rate swap
I would like to calculate returns for a plain-vanilla (fixed-for-floating) interest rate swap. Consider, that I am long in USD 5-year swap rate, i.e. I'm holding a receiver swap for 5-year swap rate with notional of 100 $. At initiation, the swap should be valued at 0 $, as both the fixed leg and the floating leg of the swap should have the same value.
If I valuate the receiver swap a month later and it would have a value of let's say 2$, then how should I calculate the return? Is it just (2$ - 0$) / 100 $, i.e. change of price relative to the notional? I can't quite figure out how I could calculate the return by comparing change of price to previous price, as it can be at initiation 0$. On the other hand, why should I calculate the return relative to notional? After all, I am not investing any capital on the swap.