We're able to approve borrowers in MI down to a 620 fico score up to a 50% debt-to-income ratio through our FHA lending relationships with an FHA automated underwriting approval and "compensating factors" (job stability, reserves, etc).
Back-end dti or ratio means (or is calculated by) dividing the proposed housing payment + the minimum monthly payments appearing on a borrwers credit report by the gross monthly income.
Please feel free to contact me directly if you need assistance with your mortgage, I'd be happy to help.
I did an FHA loan with 56% back end DTI in September 2010.
It all depends on what the automated underwriting comes back with.