How do you estimate your monthly mortgage payment?

[Trey Crusey]

I'm looking at running a Facebook ad on buying vs renting. Are there any mortgage payment calculators out there that you all have found more accurate than others? A formula to use?

I want the prospect to essentially tell me how much they're paying in rent and I'll send them some houses that are on the market they can buy for what they're paying in rent. What I'm running into is all of the calculators out there I've seen vary widely and I don't want to bug my lenders every time I get a lead. This will be for the Birmingham AL market. Any insight or tips into this would be much appreciated.  Thanks!