DTI Guide - Debt-to-Income Ratio
💰 What is Debt-to-Income (DTI) Ratio?
Your Debt-to-Income (DTI) ratio is a percentage that shows how much of your gross monthly income goes toward paying debts. It's one of the most important numbers lenders look at when deciding whether to approve your loan application.
The DTI Formula
Simple Example
Let's say you have:
Interpretation: 36.7% of your gross income goes toward debt payments. This is right at the edge of what most lenders consider acceptable.
Why DTI Matters to Lenders
Lenders use DTI to assess your ability to take on additional debt:
- Risk assessment: Higher DTI = higher risk of default
- Affordability check: Ensures you can handle new payments
- Standardised measure: Allows fair comparison between applicants
- Regulatory compliance: Many lending rules require DTI limits
According to industry reports, about 40-48% of mortgage applications are denied due to high DTI ratios. It's the most common reason for rejection, even more common than poor credit scores.
What Counts as Debt?
Include These Monthly Payments:
- Mortgage or rent payments
- Property taxes and homeowners insurance (if not in mortgage)
- Car loans and lease payments
- Student loans
- Personal loans
- Credit card minimum payments (even if you pay in full)
- Home equity loans or lines of credit
- Child support or alimony payments
- Other instalment loans
Do NOT Include:
- Utilities (electricity, water, gas)
- Groceries
- Insurance premiums (except home/mortgage insurance)
- Transportation costs (gas, parking)
- Entertainment and subscriptions
- Medical expenses
- Income tax
Many people forget to include credit card payments in their DTI calculation. Even if you pay your balance in full every month, lenders count the minimum payment as debt. Also, if you're co-signed on a loan, that payment counts toward your DTI even if someone else makes the payments.
What is Gross Monthly Income?
Your gross monthly income is the total amount you earn BEFORE taxes and deductions. Include:
- Base salary or hourly wages
- Bonuses and commissions (averaged)
- Overtime pay (if consistent)
- Rental income
- Investment income (dividends, interest)
- Alimony or child support received
- Part-time or side business income
Calculating Monthly Income from Annual Salary:
For Hourly Workers:
DTI Benchmarks
| DTI Range | Rating | Lender Perspective |
|---|---|---|
| Under 20% | Excellent | Very low risk, excellent approval odds |
| 20-28% | Very Good | Low risk, strong approval odds |
| 28-36% | Good | Manageable, acceptable for most loans |
| 36-41% | Fair | Higher risk, may need strong credit to compensate |
| 41-45% | High Risk | Difficult to get approved, limited options |
| Over 45% | Very High Risk | Approval very unlikely, need to reduce debt first |
🏠 Understanding Front-End and Back-End DTI
Lenders actually look at TWO types of DTI ratios when evaluating mortgage applications.
Front-End DTI (Housing Ratio)
This ratio only looks at housing-related expenses compared to income.
Housing Costs Include:
- Mortgage principal and interest payment
- Property taxes
- Homeowners insurance
- HOA or body corporate fees
- Mortgage insurance (if applicable)
Example:
Standard Limit: Most lenders prefer front-end DTI under 28%, though some accept up to 31% for certain loan types.
Back-End DTI (Total Debt Ratio)
This is the more comprehensive ratio that includes ALL your monthly debt obligations.
Using the Same Example Above, Add:
Standard Limit: Most lenders want back-end DTI under 36%, though some conventional loans accept up to 43-45%.
DTI Limits by Loan Type
| Loan Type | Front-End DTI Limit | Back-End DTI Limit |
|---|---|---|
| Conventional Loan | 28% | 36% (up to 45% with strong credit) |
| FHA Loan (US) | 31% | 43% |
| VA Loan (US) | No limit | 41% (flexible with review) |
| USDA Loan (US) | No limit | 41% |
| NZ Bank Mortgage | Varies | 30-40% typical |
While DTI limits exist, they're not absolute. Lenders may approve loans with higher DTI if you have: excellent credit score (750+), large down payment (20%+), significant cash reserves, stable employment history, or low debt outside the mortgage.
When DTI is Measured
Lenders calculate your DTI at different stages:
- Pre-qualification: Initial estimate based on what you tell them
- Pre-approval: Verified DTI based on documentation
- Final underwriting: Comprehensive review before closing
Once you're pre-approved for a mortgage, do NOT take on new debt (car loans, credit cards, etc.) before closing. This will change your DTI and could cause your mortgage approval to be revoked. Wait until after you've moved into your new home.
DTI vs Credit Score
These are related but different:
| DTI Ratio | Credit Score |
|---|---|
| Measures debt relative to income | Measures creditworthiness and payment history |
| Income IS considered | Income NOT considered |
| Recalculated for each loan application | Updated monthly by credit bureaus |
| Not visible on credit reports | Visible on credit reports |
| Affects loan amount qualification | Affects interest rate and approval |
🌍 Real-World DTI Scenarios
Let's look at practical examples showing different DTI situations.
Situation: Emma is 28 and wants to buy her first home.
Emma's Finances:
Current DTI (Before Mortgage):
Proposed Mortgage:
New DTI (With Mortgage):
Situation: James earns a high salary but has significant existing debt.
James's Finances:
Proposed Mortgage:
DTI Calculation:
James's 48.9% back-end DTI exceeds most lenders' limits (43-45% maximum). Despite his high income, the existing debt is too burdensome. Options: Pay off the $400 personal loan, reduce the mortgage amount, or find a co-borrower.
If James Pays Off Personal Loan:
Still high, but now within range for approval with strong credit.
Situation: Mike and Sarah are married and buying their first home together.
Combined Finances:
Proposed Mortgage:
DTI Calculation:
Situation: Lisa has a DTI of 44% and needs to get it under 36% to qualify.
Lisa's Current Situation:
Target Calculation:
Lisa's Debt Breakdown:
- Proposed mortgage: $1,200 (can't reduce without buying cheaper home)
- Car payment: $450
- Student loan: $300
- Credit Card 1: $150
- Credit Card 2: $100
Option 1: Pay Off Smallest Debts
If Lisa has $3,000 in savings, she could pay off Credit Card 2 entirely:
Option 2: Refinance Car Loan
Extend car loan from 4 years to 6 years remaining:
Option 3: Combination Approach
Refinance car + pay off one credit card:
Option 4: Best Solution
Combination + wait to pay down CC1 further:
Lisa could also:
- Increase income with side work ($200/month extra = 36.9% DTI)
- Get a co-signer/co-borrower
- Choose a less expensive home (reduce mortgage payment)
🎯 Test Your Knowledge
Complete this 10-question quiz to check your understanding of DTI
Frequently Asked Questions
What is a debt-to-income (DTI) ratio?
Your total borrowing as a multiple of your gross annual income. The Reserve Bank uses DTI limits to cap higher-risk mortgage lending.
What are the DTI limits in New Zealand?
The limits cap most owner-occupier and investor lending at a set multiple of income, with a small speed-limit allowance for loans above the cap.
How is DTI calculated?
Total debt divided by gross income. For example, $600,000 of lending on $100,000 of income is a DTI of 6.
Do DTI limits apply to everyone?
They apply to most new mortgage lending, with some exemptions such as new builds, and a limited share of higher-DTI loans is still allowed.
Situations like yours. The 4 situations worked through above sit alongside 40 more about buying a first home, each with the sums shown.