Debt-to-Income Ratio: How Lenders and Co-ops Calculate It
How to calculate front-end and back-end DTI, what counts as debt, Fannie Mae limits of 36%, 45% and 50%, and why NYC co-op boards often want 25% to 30%.
6 min read · Updated
Your debt-to-income ratio (DTI) is your monthly debt payments, including the new housing payment, divided by your gross monthly income. Fannie Mae allows up to 50% for loans approved through its automated system, but NYC co-op boards commonly want 25% to 30%, so in New York the board's limit is often the one that actually binds.
This guide shows how both versions are calculated, what counts as debt, and a worked example that passes a lender easily but is borderline at a strict co-op.
At a glance
- Formula
- Monthly debts ÷ gross monthly income
- CFPB definition
- Fannie Mae (automated)
- Up to 50%
- Desktop Underwriter maximum
- Fannie Mae (manual)
- 36%, up to 45%
- 45% needs credit score and reserves
- NYC co-ops
- Often 25%–30%
- Set by each board, not by law
Front-end vs back-end DTI
People use two versions of the ratio:
- Front-end (housing) ratio: only the housing payment divided by gross monthly income. For a house or condo that's principal, interest, property tax, insurance and any HOA or common charges. For a co-op it's the share-loan payment plus monthly maintenance.
- Back-end (total) ratio: housing plus every other recurring debt payment, divided by gross monthly income. This is the number Fannie Mae's limits refer to and what the CFPB means by DTI.
The CFPB's own example: $1,500 mortgage + $100 car loan + $400 other debts = $2,000 a month. Divided by $6,000 of gross monthly income, the DTI is 33%.
What counts as debt
Lenders count required monthly payments, not your spending. Fannie Mae's rules include:
| Obligation | How it counts |
|---|---|
| New housing payment | Principal, interest, taxes, insurance and HOA dues (PITIA) for a principal residence |
| Credit cards | The minimum payment on the report; if none is shown, 5% of the balance unless documents show a lower payment |
| Car loans and other installment debt | Counted if more than ten payments remain; may still count with fewer if the payment is large |
| Student loans | The payment on the report. If it shows $0 or nothing: a documented income-driven payment (which can be $0), or for deferred loans 1% of the balance or a fully amortizing payment |
| Car and other leases | Counted no matter how many months remain on the lease |
| Child support, court-ordered alimony | Counted if payments continue for more than ten months (alimony can instead be deducted from income) |
| Utilities, phone, groceries | Not on Fannie Mae’s list of debts |
Income means gross (pre-tax) income that the lender can document and expects to continue. Co-op boards may count income differently. Some leave out passive income such as dividends, according to industry sources, so ask the managing agent how the building counts it.
Lender limits by program
Fannie Mae, the largest buyer of conventional loans, sets these maximums in its Selling Guide (section B3-6-02, dated April 2, 2025):
- Loans run through Desktop Underwriter (DU): maximum DTI of 50%.
- Manually underwritten loans: 36%, which can go up to 45% if you meet the credit score and reserve requirements in Fannie Mae's eligibility matrix.
Those are ceilings, not targets. Government-backed loans (FHA, VA, USDA) have their own rules, and individual lenders can set stricter limits. As the CFPB puts it, different loan products and lenders will have different DTI limits. Ask each lender what maximum it will use for your file.
How NYC co-op boards apply DTI
Co-op boards approve buyers on their own terms, separate from your lender. According to Hauseit, which tracks NYC co-op practice, most boards look for a DTI between 25% and 30%, some accept the low 30s, and some don't publish a number at all. Boards include the monthly maintenance (and any special assessment) in the housing cost, along with your loan payment and other fixed debts.
| Fannie Mae lender | Typical NYC co-op board | |
|---|---|---|
| Usual ceiling | 50% (DU) / 36%–45% (manual) | Often 25%–30% |
| Includes co-op maintenance | ||
| Includes car, student, card payments | ||
| Written, published rule | Varies by building | |
| Can be offset by large reserves | Sometimes (45% manual tier) | Sometimes, at the board’s discretion |
Boards also test post-closing liquidity and the down payment. See co-op financial requirements and try the co-op board approval calculator.
Worked example: a $500,000 co-op
A household earns $192,000 a year, or $16,000 a month gross. They buy a $500,000 co-op with 20% down, so they borrow $400,000 for 30 years. At an illustrative 6.5% rate (not a quote), principal and interest is about $2,528 a month. Maintenance is $1,500 a month. They also pay a $450 car loan, a $300 student loan and a $50 card minimum.
| Line | Monthly |
|---|---|
| Share loan principal and interest | $2,528 |
| Co-op maintenance | $1,500 |
| Housing total | $4,028 |
| Car loan | $450 |
| Student loan | $300 |
| Credit card minimum | $50 |
| All debts | $4,828 |
| Gross monthly income | $16,000 |
| Front-end ratio ($4,028 ÷ $16,000) | 25.2% |
| Back-end ratio ($4,828 ÷ $16,000) | 30.2% |
At 30.2%, the household is far below Fannie Mae's 50% DU ceiling. But a board with a strict 30% limit could see them as just over. Paying off the $450 car loan before applying would drop the back-end ratio to about 27.4% ($4,378 ÷ $16,000).
How to lower your DTI
- 1
Pay off small installment loans
A loan with a few thousand dollars left can carry a large monthly payment. Clearing it removes the whole payment from the ratio. - 2
Pay down credit cards
Lower balances mean lower minimums, and lenders use 5% of the balance when no payment is reported. - 3
Put more down or buy for less
A smaller loan means a smaller payment. In a co-op, low maintenance matters as much as price. - 4
Document all of your income
Bonuses, freelance and rental income usually need a two-year history. Ask the lender what it will count. - 5
Fix your student loan payment on paper
If you are on an income-driven plan, give the lender the servicer letter showing your actual payment. - 6
Hold off on new debt
A new car loan between pre-approval and closing can push you over the limit.
Re-verified 2026-10-12. DTI definition, $1,500+$100+$400 / $6,000 = 33% example, and "different loan products and lenders will have different DTI limits": CFPB. Fannie Mae B3-6-02 (dated 04/02/2025): 36% manual, up to 45% with credit score and reserve requirements, 50% max for DU. B3-6-05 (dated 08/05/2026): revolving with no payment = 5% of balance; installment debts with more than ten payments remaining counted (or fewer if significant); lease payments counted regardless of months remaining; court-ordered alimony over ten months counted or deducted from income; student loans with $0/no payment use a documented IDR payment (may be $0) or, if deferred/forbearance, 1% of balance or fully amortizing payment. Fixed: lease and student-loan rows were imprecise. Worked example math re-checked ($400k at 6.5% = $2,528.27 P&I; 25.2% / 30.2% / 27.4%). Co-op range (25%–30%, some low 30s, maintenance and special assessments included, many exclude passive income) is industry practice from Hauseit, re-opened 2026-10-12; no law sets co-op DTI. Worked example uses an illustrative 6.5% 30-year rate, not a market quote; P&I computed with the standard amortization formula.
Sources
- What is a debt-to-income ratio? · Consumer Financial Protection Bureau (accessed October 12, 2026)
- Selling Guide B3-6-02, Debt-to-Income Ratios · Fannie Mae (accessed October 12, 2026)
- Selling Guide B3-6-05, Monthly Debt Obligations · Fannie Mae (accessed October 12, 2026)
- Debt-to-income ratio requirements for NYC co-ops · Hauseit (accessed October 12, 2026)
General information, not legal, tax or financial advice. Rules change; confirm with the agency or a professional before you act.