Is there a good method to accurately determine what my mortgage rate would be without using a lender? 

The wife and I both have good credit, 10+ years of credit history, and work at W-2 jobs. We're looking at purchasing a multi-family property as either our main residents or an investment property. I'd like the ability to calculate what mortgage rate I can expect to get on different properties without having to use a lender each time. 

@Mac Boeve

Are you referring to the interest rate from a seller if they financed it themselves? Seller financing can vary drastically depending on each seller's situation and motivation.

Sorry my question is a little misleading. I'm planning on getting a 30yr fixed rate mortgage from a bank. But I do not want the lender to calculate my interest rate for a property if I can get a reasonable estimate myself. Since I'm in no rush to buy it could be a year or so before we make a move and I don't want to have to get multiple credit checks if I can avoid it.