This is my first time using Black76 to value options on IR futures and I have a question on $F$ and $K$.
I understand the price for an IR future is usually quoted as $100 - r$. Do I use this price as $F$ in Black76 or do I have to use $r$ and also convert the strike $K$ to an interest rate?
If I have to use interest rates for $F$ and $K$, how should I treat negative rates i.e. strike prices greater than 100?