Two main kinds of DTI
The two main kinds of DTI are expressed as a pair using the notation
x/y (for example, 28/36).
1.The first DTI, known as the front ratio, indicates the percentage of
income that goes toward housing costs, which for renters is the rent
amount and for homeowners is PITI (PITI includes mortgage principal and
interest, mortgage insurance premium [when applicable], hazard
insurance premium, property taxes, and homeowners association dues when
applicable).
2.The second DTI, known as the back ratio, indicates the percentage of
income that goes toward paying all recurring debt payments, including
those covered by the first DTI, and other debts such as credit card
payments, car loan payments, student loan payments, child support
payments, alimony payments, and legal judgments.
Example
In order to qualify for a mortgage for which the lender requires a
debt-to-income ratio of 28/36:
Yearly Gross Income = $45,000 / Divided by 12 = $3,750 per month
income.
$3,750 Monthly Income x .28 = $1,050 allowed for housing expense.
$3,750 Monthly Income x .36 = $1,350 allowed for housing expense plus
recurring debt.
What DTI limits are used in qualifying borrowers?
United States Current limits
Conforming loans
In the U.S., for conforming loans, the following limits are currently
typical:
Conventional financing limits are typically 28/36.
FHA limits are typically 31/43.
VA limits are only calculated with one DTI of 41. (This is effectively
equal to 41/41, although VA does not use that notation.)
Nonconforming loans
Back ratio limits up to 55 have become common in recent years for
nonconforming loans. The recent spate of defaults by subprime borrowers
may produce a market correction that revises these limits downward
again. However, how large the adjustment remains to be seen.
Historical limits
The business of lending and borrowing money has evolved qualitatively
in the post-World-War-II era. It was not until that era that the FHA
and the VA (through the G.I. Bill) led the creation of a mass market in
30-year, fixed-rate, amortized mortgages. It was not until the 1970s
that the average working person carried credit card balances (more
information at Credit card#History). Thus the typical DTI limit in use
in the 1970s was PITI<25%, with no codified limit for the second DTI
ratio (the one including credit cards). In other words, in today's
notation, it could be expressed as 25/25, or perhaps more accurately,
25/NA, with the NA limit left to the discretion of lenders on a
case-by-case basis. In the following decades these limits gradually
climbed higher, and the second limit was codified (coinciding with the
evolution of modern credit scoring), as lenders determined empirically
how much risk was profitable. This empirical process continues today.