What is the 28/36 rule and how does it affect loan qualification?
The 28/36 rule is a debt-to-income guideline used by lenders to qualify borrowers. The 28% ratio limits housing expense (principal, interest, taxes, insurance, HOA) to 28% of gross monthly income. The 36% ratio limits total debt (housing plus all other debts) to 36% of gross monthly income. Example: $5,000 monthly income; max housing expense is $1,400; max total debt is $1,800.
Key Takeaways
- The 28/36 rule is a debt-to-income guideline used by lenders to qualify borrowers.
- The 28% ratio limits housing expense (principal, interest, taxes, insurance, HOA) to 28% of gross monthly income.
- The 36% ratio limits total debt (housing plus all other debts) to 36% of gross monthly income.
- Example: $5,000 monthly income; max housing expense is $1,400; max total debt is $1,800.
- Exam questions test whether you can calculate both ratios and determine the limiting factor.
Real Estate Math on the Real Estate Exam
Most residential mortgage lenders use the 28/36 rule (or variations like 29/41) to assess borrower creditworthiness. Understanding these ratios helps you evaluate a buyer's borrowing capacity, advise on affordability, and identify which borrowers qualify for which loan amounts. Exam questions test whether you can calculate both ratios and determine the limiting factor. Real estate professionals must understand loan qualification even though lenders make final decisions.
Understanding Real Estate Math: Key Concepts
What It Means
The 28/36 rule (also called debt-to-income ratio or DTI) is the most common underwriting guideline for residential mortgages. It consists of two separate ratios that must both be satisfied.
The 28% ratio, called the 'front-end ratio' or 'housing ratio,' limits the monthly housing payment to 28% of the borrower's gross monthly income. Housing expense includes principal and interest (P and I), property taxes, homeowner's insurance, and HOA fees if applicable. This is often abbreviated as PITI (principal, interest, taxes, insurance). For example, if a borrower's gross monthly income is $5,000, the maximum housing payment is $5,000 times 0.28 equals $1,400 per month.
The 36% ratio, called the 'back-end ratio' or 'total debt ratio,' limits the total monthly debt obligation to 36% of gross monthly income. Total debt includes the housing payment plus all other monthly debt payments: car loans, student loans, credit cards (using minimum payments), child support, alimony, and any other recurring obligations. Using the same $5,000 income example, maximum total debt is $5,000 times 0.36 equals $1,800 per month. This means if housing is $1,400, the borrower can have at most $400 in other debt ($1,800 minus $1,400).
Additional Considerations
The 28 and 36 ratios work together: the borrower must satisfy both. Sometimes the 28% housing limit is the constraint; sometimes the 36% total debt limit is tighter, depending on the borrower's existing obligations. This is why you must calculate both and determine which is more restrictive.
Common exam questions ask you to: (1) calculate maximum housing expense using the 28% ratio, (2) calculate maximum total debt using the 36% ratio, (3) identify which ratio limits the borrower, and (4) determine the maximum loan amount the borrower can qualify for. For the loan amount calculation, you may need to work backwards from the housing payment to find the loan amount. This requires understanding loan payment formulas or using provided payment tables.
Variations: Some lenders use 29/41 or 31/43 ratios for borrowers with excellent credit or large down payments. Some loans (FHA, VA, USDA) have their own guidelines that differ from 28/36. The exam will specify which ratio to use; do not assume 28/36 unless stated.
Real Estate Math Rules by State
Each state has its own rules when it comes to real estate math. Here are a few examples of how requirements differ:
California
California does not mandate specific debt-to-income ratios; lenders set their own underwriting standards. However, most California lenders use 28/36 or similar guidelines. Fannie Mae and Freddie Mac conforming loans (up to loan limits) typically use 28/36. Exam questions use standard ratios unless otherwise specified.
Texas
Texas does not impose DTI requirements at the state level; ratios are set by individual lenders. Conventional conforming loans use 28/36 or variations. Exam questions in Texas follow national standards unless the question specifies a different ratio. Focus on understanding the calculation method, not state-specific percentages.
Florida
Florida does not mandate debt-to-income ratios; lenders establish their own standards. Most use 28/36 for conventional loans. Some lenders may adjust ratios for retirement income or other factors. Exam questions use standard 28/36 unless the problem specifies otherwise.
Always calculate both the 28% and 36% limits and identify which one is more restrictive for the borrower. Do not assume the 28% is always the limiting factor; if a borrower has significant other debt, the 36% total debt ratio may be tighter. Be careful with the definition of 'gross monthly income'; use income before taxes, not after-tax take-home. If the question provides annual income, divide by 12 to get monthly. Watch for trick questions where existing debt obligations determine qualification capacity more than the housing ratio.
Rules vary across all 50 states
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