Divide the monthly rent the lender will count by the full monthly payment: principal, interest, property taxes, insurance and any HOA dues (PITIA). A home that rents for $2,400 with a $1,920 PITIA has a DSCR of 1.25. The arithmetic is easy; the hard part is using the same rent and payment figures the underwriter will use.
Which formula do residential DSCR loans use?
Most DSCR loans on one-to-four unit rentals use a simple version of the ratio: DSCR equals gross monthly rent divided by the monthly PITIA payment. Gross rent means the rent before you subtract repairs, management or vacancy. PITIA stands for principal, interest, taxes, insurance and association dues. Some programs label the bottom of the fraction "PITIA" and others say "ITIA" when the loan is interest-only, but the idea is identical: the full monthly cost of carrying the debt on that property.
That simplicity is the point. A traditional mortgage asks how your personal income compares with all of your personal debts. A DSCR loan asks a narrower question about the property itself: does what it rents for cover what it costs to finance and hold? Because both numbers come from the property, the ratio can be checked without tax returns or pay stubs.
Commercial lenders use a different formula with the same name, built on net operating income and annual debt service. If you have seen that version in a textbook, read our guide on commercial versus rental DSCR so the two do not get mixed up. Everything in this guide refers to the residential investor version.
Which rental income will the lender count?
Start with the top of the fraction, because it is where most do-it-yourself calculations go wrong. On a purchase, the property usually has no lease you are taking over, so the lender typically relies on the appraiser's estimate of market rent, completed on a rent schedule form. On a refinance, a signed lease may be used, sometimes compared against that same market rent estimate, and some programs use the lower of the two.
The figure you type into a calculator should therefore be the rent a neutral appraiser would agree with, not the best listing you found online. Look at what similar homes nearby actually leased for recently. If your number is noticeably higher than those comparables, expect it to be trimmed, and run the ratio at the lower figure too.
What belongs in the full monthly payment?
The bottom of the fraction has five pieces. Principal and interest come from the loan amount, the rate on your quote and the amortization term. Property taxes come from the tax bill, divided by twelve. Insurance comes from a quote for a landlord or dwelling policy, also divided by twelve. HOA dues are added if the property has an association. Flood insurance, if required, belongs here too.
On a purchase, be careful with taxes. In many counties the tax bill is reassessed after a sale, so the seller's current bill may understate what you will pay. Underwriters often estimate taxes on the purchase price rather than the old assessment. Using the higher figure in your own math keeps you from being surprised.
- Principal and interest: from the loan amount, your quoted rate and the term
- Taxes: annual bill divided by twelve, estimated on the new value for a purchase
- Insurance: annual landlord policy premium divided by twelve
- Association dues: the monthly HOA or condo fee, if any
- Other required escrows, such as flood insurance in a mapped flood zone
How do you calculate and interpret the ratio?
Now divide rent by the payment. Here are three worked examples using round numbers you can check with a calculator.
Example A, a single-family rental: market rent is $2,400 a month. Principal and interest are $1,480, taxes are $260, insurance is $130 and there is a $50 HOA. The PITIA is $1,920, and 2,400 ÷ 1,920 = 1.25. The rent covers the payment with $480 left over each month before repairs and vacancy.
Example B, the same house with a bigger loan: if a smaller down payment raises principal and interest to $1,790, the PITIA becomes $2,230, and 2,400 ÷ 2,230 = 1.08. Same property, same rent, but a much thinner cushion. This is why the loan amount you choose matters as much as the property.
Example C, a duplex: two units rent for $1,350 and $1,250, so gross rent is $2,600. With a PITIA of $2,750, the ratio is 2,600 ÷ 2,750 = 0.95. The rent falls short of the payment by $150 a month. Some programs can still work with a ratio under 1.00, usually with tradeoffs, but the owner would be feeding the property every month.
Which DSCR calculation mistakes should you avoid?
Most errors come from leaving something out of the payment or being optimistic about rent. A few patterns show up again and again when investors compare their own ratio with the one an underwriter produces.
- Dividing rent by principal and interest only, which can make a weak deal look comfortable
- Using the seller's current tax bill instead of a post-sale estimate
- Using an owner-occupant homeowner's insurance quote instead of a landlord policy
- Using asking rents instead of leased comparables
- Forgetting the HOA, or a special assessment that is already scheduled
- Subtracting vacancy and repairs from rent, which most residential DSCR programs do not do
Why might your DSCR differ from the lender’s calculation?
Even with careful inputs, two wholesale lenders can land on slightly different ratios for the same property. One might use the lease, another the appraised market rent. One might qualify an interest-only loan on the interest-only payment, another on a fully amortizing payment. Each sets its own minimum ratio and its own rules for what counts. Your calculation is a strong estimate, not the final word.
That variation is useful, not just annoying. As a mortgage broker, we arrange and shop financing from wholesale lenders, so we can see how several programs would read the same file. If your ratio sits near a program's cutoff, the difference in how each one calculates can decide which options you have.
Before you make an offer, run the numbers in our DSCR calculator with conservative rent and full PITIA. If the ratio still works, you have a property that pays for its own financing. If it only works with optimistic inputs, you have learned that cheaply.
What else should you know about this topic?
What is the DSCR formula for a rental property?
For most residential DSCR loans, DSCR equals gross monthly rent divided by the monthly PITIA payment: principal, interest, property taxes, insurance and HOA dues.
Do I subtract vacancy and repairs before calculating DSCR?
Usually not for one-to-four unit DSCR loans. Most programs use gross rent over PITIA. Track vacancy and repairs in your own budget, because the ratio does not include them.
Which rent figure does the lender use on a purchase?
Typically the appraiser's market rent estimate, because there is usually no lease you are assuming. On a refinance a current lease may be used if the program allows it.