Where do I find T BILL RATE and IV to calculate option premium

I am trying to create a premium calculator, but I can't find these variable.

https://zerodha.com/tools/black-scholes/ by default says IV: 18% and Interest %: 7%. Is that correct?

RBI site says "364-Day Treasury Bill (Primary) Yield" = 3.63%

Which one is correct, and how to calculate IV?
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