BRRRR Cashout refi, minimum 6 months?

[Chris Roche]

I am researching buying a property using the BRRRR method. My strategy will be to buy using hard money, rehab using my HELOC (lower interest than hard money) and then cash out refi on the back end.

Two Questions:

Do all lenders require you to wait 6 months after purchase to cash out refi conventional?  I asked a lender today and he said that Fannie Mae guidelines require banks to wait 6 months to refi.

Is there a simple calculator to calculate interest only payments.  Ex.  if loan amount is $150,000, 6 month minimum loan, no prepayment penalties, what will loan amount be?

Thanks!