Honestly, 0

Anytime I have ever been on an interview in the last 40 years I have been offered the job.

I have turned a few down as I did not like the conditions, or pay or whatever, but I have at least had an offer.

Now that does mean I have applied for jobs and not even made it to the interview stage. There are hundreds of those. But any time I have had an interview there has always been an offer.