Quote from heech:
Continuing with this thought experiment (which I'll probably test out with some orders tomorrow):
- I fill an order to "buy 25000 VAF3 @ 19.5", which gives me long 3543 futures at 782.54 each.
- Same day, implied goes up enough that I fill an order to "sell 25000 VAF3 @ 20.5". According to the calculator, this is equivalent to selling 3370 futures at 789.78 each.
Net result: realized gains of $24399, but I'm still net long 173 futures.
So... what's interesting is that this doesn't actually leave you with a flat position. Selling 25000 vega notional at 20.50 is not the same thing as buying 25000 vega notional at 19.50. If I want to fully flatten my full 3543 futures, I should have sold vega notional of 26,263 @ 20.50.
I mean, you can see why retail guys are going to have a hard time with this... you can't flatten by selling the same "quantity" you bought earlier. You literally HAVE to pull out the calculator and figure out the correct numbers.