Most first-time rental buyers call a lender before they understand the deal. That order is backwards. The loan you can get is a direct function of what the property earns, so the smart approach is to underwrite the building first and let the financing fall out of the math.
Take a scenario that plays out constantly. A duplex is listed at $310,000. The two units rent for $1,250 and $1,150 a month. Before you call a broker, before you write an offer, before you drop $600 on an inspection, you can estimate what loan you’ll qualify for, what it will cost, and how much cash you need at closing. Here’s how that works, step by step.
Unit Count Decides Which Rulebook You’re Using
The single biggest factor in a rental property mortgage is how many units sit on the property. One to four units is financed as residential real estate. Same lenders, same basic products, same 30-year fixed options you’d see on a house you live in.
Five units or more is commercial. You’re now dealing with different lenders, shorter amortization schedules (often 20 or 25 years), higher rates, and underwriting that leans heavily on the property’s income statement. Some banks won’t touch anything under $1 million.
This is why four-unit buildings are so popular with small investors. They’re the largest property you can buy with residential financing, and the extra units spread your fixed costs. If you’re eyeing that sweet spot, financing a four-unit property works almost identically to a duplex, just with more rent and more tenants to manage.
Step 1: Run the Property Like a Lender Would
Lenders don’t care how nice the kitchen is. They care about four numbers, and you should care about them in the same order.
The numbers that actually decide the loan
- Net operating income (NOI): Rent collected minus operating expenses, before the mortgage payment. Taxes and insurance count as expenses. So do vacancy, repairs, and management, even if you plan to self-manage.
- Debt service coverage ratio (DSCR): NOI divided by your annual mortgage payment. Most rental-focused lenders want 1.0 to 1.25. Below 1.0 means the property doesn’t cover its own loan.
- Loan-to-value (LTV): The loan amount relative to the purchase price or appraised value, whichever is lower. This is what your down payment controls.
- Reserves: Cash left in the bank after closing. Typically two to six months of payments, and often more per property once you own several.
Now run the duplex. Gross rents are $2,400 a month, or $28,800 a year. Subtract vacancy at 5% ($1,440), repairs at 8% ($2,304), capital reserves at 5% ($1,440), management at 8% ($2,304), property taxes at $3,600, and insurance at $1,500. That’s $12,588 in expenses, leaving an NOI of $16,212 a year, or about $1,351 a month.
Put 25% down and you’re borrowing $232,500. At 7.25% over 30 years, principal and interest run about $1,586 a month. Divide $1,351 by $1,586 and your DSCR is 0.85. The property doesn’t cover the loan at that down payment.
Bump to 30% down and the payment drops to roughly $1,480, pushing DSCR to 0.91. Still short. At 40% down you’re borrowing $186,000, paying about $1,269 a month, and the DSCR lands at 1.06. That’s the number that clears most lenders’ bars.
In other words, this specific duplex needs somewhere around 38% to 40% down to work as a DSCR deal. Knowing that before you tour the building is worth more than any rate quote.
Step 2: Match the Program to the Deal You Found
Once you know your numbers, pick the loan type that fits. There are three realistic paths for a small rental.
Conventional investment property loans
Best rates, strictest rules. Expect 15% to 25% down depending on unit count, and you’ll qualify on your personal income and total debt-to-income ratio rather than the property’s DSCR alone. Rental income can offset the new payment, but lenders typically only count 75% of it. Fannie Mae also caps how many financed properties you can carry, generally up to ten.
DSCR loans
These qualify on the property’s income only. No tax returns, no pay stubs, no DTI calculation. Rates usually run half a point to a point and a half above conventional, and down payments start around 20% to 25% but climb quickly when the DSCR is thin. The trade-off is speed and flexibility, plus the ability to close in an LLC.
Second home and house-hack hybrids
If you’ll spend part of the year there or live in one unit, you may qualify for owner-occupied pricing, which can be dramatically cheaper. The rules around occupancy, distance from your primary residence, and rental use are strict, so read up on how a second home mortgage treats a property you also rent out before assuming you qualify.
Step 3: Build the File Before You Tour the Building
Approval speed wins deals in competitive markets. Having this folder ready before you write an offer puts you in a completely different category than the buyer who starts scrambling after the inspection.
- Two years of personal tax returns, all schedules, plus the last two months of bank and brokerage statements
- A rent roll for the property, with lease start dates and current payments for each unit
- The seller’s most recent tax bill and insurance declaration page, or your own quotes if they aren’t available
- A written scope for any repairs you plan to make, especially if you’re asking for a credit
- Proof of reserves, including retirement accounts if the lender allows them
If you already own rentals, add their leases, mortgage statements, and tax returns to the pile. Every existing property you own gets counted against your reserves and your debt load, whether or not it’s profitable.
Step 4: Compare Offers on Total Cost, Not Just Rate
Two lenders quoting 7.25% can produce wildly different closings. Ask each one for a full Loan Estimate and compare the same line items across all of them.
Watch for origination points, underwriting fees, and rate buydowns disguised as discounts. On DSCR loans, look hard at prepayment penalties, which can run three to five years on a step-down schedule and lock you out of a refinance if rates fall. A six-step walkthrough of getting an investment property mortgage is useful here, because the pricing gaps between lenders are widest on exactly the loans investors use most.
Get at least three quotes. On a $232,500 loan, half a point of rate is roughly $70 a month, or $25,000 over the life of the loan.
Step 5: When the Numbers Don’t Clear the Bar, Change the Structure
Plenty of good properties fail the first pass. The duplex above needed 40% down at the asking price. That doesn’t mean walk away. It means adjust one of four levers.
Negotiate the price. At $275,000 with 25% down, you’d borrow $206,250, pay about $1,407 a month, and hit a DSCR of roughly 0.96. Push to $265,000 and you’re right at 1.0. Sellers who’ve been sitting on a vacant unit for 60 days are often more flexible than they let on.
Raise rents at turnover. A $150 monthly increase across two units adds $3,600 a year to NOI. That flows straight into the DSCR calculation, and appraisers will count signed leases at the higher amount.
Ask the seller for a credit. A $10,000 credit toward closing costs keeps your cash in the bank and helps you clear the reserves requirement, even though it doesn’t change the loan amount.
Bring in a partner. Splitting the down payment gets you past the cash hurdle, but you’ll need a written operating agreement covering who decides on repairs, how distributions work, and what happens if one of you wants out.
What you should not do is stretch to a loan that barely covers itself and then hope nothing goes wrong. A single month of vacancy plus a $4,000 furnace replacement can turn a 1.05 DSCR into a cash call out of your own pocket. Investors who survive their first downturn are the ones who left margin in the deal. There’s a reason experienced buyers talk so much about financing a rental without getting burned, and it has almost nothing to do with the interest rate.
Run the four numbers before you call anyone. Pick the program the numbers point to. Then go find the lender who prices it best, with a folder already in hand. Do that and the mortgage becomes the easy part of buying a rental, which is exactly where it belongs.