debt payment caculation

[Brandon Turner]

I have been playing around with a debt calculation sure people have done this before. Debt service (principal and interest only/ gross rent.  I keep coming up with about 40% would be the maximum I would want to pay for a property. Example a property rents for $1000 debt service is $400.00. Has anyone else done something like this. I was also figuring it on a 15 year note. IF so in that scenario am I being too conservative?