How to Analyze a Duplex When One Unit Is Already Rented

You found a duplex you like, but there's a catch: one unit already has a tenant. This changes your analysis in ways that trip up a lot of first-time buyers. The existing lease (understand tenant rights first) affects your timeline, your financing options, and most importantly, whether the numbers you're running reflect reality.

The rule is simple: model the months left on the lease at the rent the tenant pays today, and only switch to market rent after the lease ends. In the example below, a $285,000 duplex with a tenant paying $1,150 against a $1,400 market costs the owner-occupant $12,530 out of pocket in year one ($1,044 a month), then produces $272 a month and a 5.0% cash-on-cash return once both units are rented at market. Using market rent from day one would have overstated year one by $1,250. If you plan to live in the other unit, you can run this in the house hack calculator.

I've bought properties with tenants in place and inherited some real headaches. I've also found deals where the existing tenant made the whole thing work. The difference came down to how carefully I analyzed the situation before making an offer.

Why an Existing Tenant Changes Everything

When you buy a property with a tenant already living there, you inherit more than just rental income. You inherit their lease, their security deposit, their maintenance history, and whatever relationship they have with the current owner.

This matters because:

• The lease terms are binding on you as the new owner
• You can't just raise rent to market rate on day one
• The tenant's payment history might not match what the seller claims
• Deferred maintenance issues often surface after closing

The seller has an incentive to make the rental income look as good as possible. Your job is to verify everything independently.

Getting the Real Numbers

Verify Current Rent Against Market

The first thing I do is compare the existing rent to current market rates for similar units in the same neighborhood. Pull comps from Zillow, Apartments.com, and Craigslist, and check the rent estimate tool. Call a few property managers and ask what they'd expect the unit to rent for.

Say the tenant is paying $1,100/month. If comparable units are renting for $1,350/month, you're looking at $250/month of upside, but only after the current lease ends. If the lease runs another 8 months, that's 8 months of below-market income ($2,000 in total) you need to factor into your analysis.

On the flip side, if the tenant is paying $1,400/month and market rate is $1,200/month, you have a problem. When that lease ends, you're probably losing $200/month unless you have a very good reason to believe you can maintain that premium.

Request These Documents

Before you get serious about an offer, ask the seller for:

• Current lease agreement (not a summary, the full signed document)
• Rent roll showing payment history for at least 12 months
• Security deposit amount and where it's held
• Any lease addendums or modifications
• Utility bills for the past 12 months if landlord-paid
• Maintenance records for the occupied unit
• A tenant estoppel certificate, which is a short form the tenant signs confirming the rent, the deposit, the lease dates and any side agreements with the seller

If the seller can't produce these documents, that tells you something. Either they're disorganized (which often means deferred maintenance) or the numbers won't look good under scrutiny. The post on verifying seller rent rolls goes deeper on how to check what you're given.

Talk to the Tenant

This is awkward, but worth it. After you're under contract and during the inspection period, ask to meet the tenant. I usually bring a small gift card or something to make it feel less like an interrogation.

Questions I ask:

• How long have you lived here?
• How has the landlord been about repairs?
• Anything broken right now that hasn't been fixed?
• Planning to stay or move when your lease ends?

That last question matters for your projections. If they're planning to leave in 3 months, you need to budget for turnover costs and vacancy.

How to Model the Cash Flow

Here's where most buyers mess up: they either use the current rent and assume it continues forever, or they use market rent and assume they can get it immediately. Neither is accurate.

The Right Approach

Model your first year using the rent from the existing lease for as long as that lease runs. Then model the following months and years at market rent, minus a reasonable vacancy factor.

Here's a framework, using a lease with six months left as the example:

If the current tenant might leave when the lease ends, add a turnover cost (typically one month's rent for cleaning, repairs, and marketing) and at least one month of vacancy.

Below-Market Rent Scenarios

Below-market rent isn't always bad. It depends on why.

Acceptable reasons:

• Long-term tenant who's been there 5+ years and rent increases were modest
• Tenant handles minor maintenance themselves
• Property needs cosmetic updates that would justify higher rent

Red flags:

• Rent hasn't increased in 3+ years for no clear reason
• Tenant is a family member or friend of the seller
• Lease was just signed at below-market rate before listing

That last one happens more than you'd think. Seller locks in a 2-year lease at low rent right before listing to show "stable tenancy." You're stuck with it. For a fuller treatment of pricing a deal around a low rent, see analyzing a rental property with below-market rents and the companion post on below-market leases.

A Worked Example

Let's run through a full scenario. The interest rate is an example, not a quote.

Property Details:

• Purchase price: $285,000
• Down payment: 20% ($57,000)
• Loan amount: $228,000 at an example 7.25% (30-year fixed)
• Monthly P&I: $1,555

Unit A (Currently Rented):

• Current rent: $1,150/month
• Lease expires in 5 months
• Market rent: $1,400/month
• Tenant says they plan to stay

Unit B (Vacant, you'll occupy):

• Estimated rent if you moved out: $1,350/month
• You'll house-hack for year one

Monthly Expenses:

• Property taxes: $285/month
• Insurance: $150/month
• Maintenance reserve: $200/month
• CapEx reserve: $150/month
• Vacancy allowance (5%): Applied once both units are rented

Year One Cash Flow (House-Hacking)

Months 1-5 (current lease):

• Income: $1,150
• Expenses: $285 + $150 + $200 + $150 = $785
• Net Operating Income: $365
• Mortgage: $1,555
• Monthly Cash Flow: -$1,190

You're covering $1,190/month out of pocket while living in Unit B.

Months 6-12 (after lease renewal at market):

• Income: $1,400
• Same expenses: $785
• NOI: $615
• Mortgage: $1,555
• Monthly Cash Flow: -$940

Year One Total:

• Months 1-5: -$1,190 x 5 = -$5,950
• Months 6-12: -$940 x 7 = -$6,580
• Total out-of-pocket: $12,530

That's $1,044/month average, and $350 of it is reserves you keep if nothing breaks. Compare that to what you'd pay in rent elsewhere. If apartments in your area run $1,500/month, you're saving $456/month while building equity. Not a home run, but not bad.

What If the Tenant Doesn't Renew at Market?

The base case leans on the tenant staying and accepting a $250 increase. Here is how year one moves if that doesn't happen:

The spread between best and worst is $2,800. If that swing would strain your budget, the deal is too tight. A jump from $1,150 to $1,400 is also a 22% increase, which many tenants will not absorb in one step and some jurisdictions will not allow, so treat the middle row as a realistic outcome, not a remote one.

Year Two Cash Flow (Both Units Rented)

You move out and rent both units at market.

• Gross rent: $1,400 + $1,350 = $2,750
• Vacancy (5%): -$138
• Effective Gross Income: $2,612
• Expenses: $785
• NOI: $1,827
• Mortgage: $1,555
• Monthly Cash Flow: $272

Annual cash-on-cash return:

• Cash flow: $272 x 12 = $3,264
• Total cash invested: $57,000 (down payment) + about $8,000 (closing costs) = $65,000
• Cash-on-cash: 3,264 / 65,000 = 5.0%

That's modest, but you also lived below market rent for a year. Add principal paydown (about $2,400 in year two) and the total return looks better than the cash flow alone. The cash-on-cash return guide explains how to read that 5.0% against other uses of $65,000.

Lease Assignment: What Actually Happens at Closing

In most places the lease survives the sale, which means you become the landlord under the existing terms whether or not anyone signs a new document. The assignment paperwork is how you prove it, get the deposit, and avoid arguments later.

At closing, make sure:

1. The lease assignment document is signed by seller and buyer, and the tenant is notified in writing of the new owner and where to pay
2. Security deposit is transferred to you (usually as a credit at closing)
3. You have the complete signed lease and every addendum
4. Prorated rent is handled correctly (if closing mid-month)

Some buyers skip the formal assignment and just start collecting rent. This works until there's a dispute, often over a deposit the tenant paid and you never received. Get the paperwork right.

Financing Considerations

Lenders look at tenant-occupied properties differently depending on how you'll use the property.

If you're house-hacking (living in one unit):

• You'll likely use a conventional loan, FHA or VA, and you generally need to move in within about 60 days, so one unit has to be vacant or about to be
• Lenders may count 75% of the rental income to help you qualify
• The existing tenant's rent helps your debt-to-income ratio, though with a lease in place the lender may use the lease rent when it is lower than the market estimate

The low down payment options are covered in house hacking with 5% down conventional loans, and the house hacking guide covers the strategy as a whole.

If you're buying as a pure investment:

• Expect a larger down payment (25% is common on two to four units) and a closer look at the existing lease
• Some lenders want to see a meaningful term remaining on the lease
• Below-market rent might hurt your loan amount when the lender uses the lease rent, not market rent

For a pure rental, run the numbers in the single family and small multifamily calculator instead. Ask your lender how they'll treat the existing rental income before you get too far into the process.

Common Mistakes When Analyzing Tenant-Occupied Duplexes

Trusting the Seller's Rent Roll Without Verification

I've seen rent rolls that showed perfect on-time payment for 24 straight months. Then I asked the tenant directly and learned rent had been late 6 times in the past year. The seller just didn't record it that way.

Verify payment history through bank statements or canceled checks if possible. At minimum, ask the tenant about their payment history and watch their reaction.

Ignoring the Lease End Date in Your Projections

If the lease ends 2 months after you close and the tenant leaves, your year-one cash flow looks nothing like what you modeled. Budget for the realistic scenario, not the optimistic one.

A lease ending soon isn't necessarily bad. It gives you flexibility to renovate, raise rent, or bring in a tenant you've vetted yourself. But you need to plan for the transition.

Assuming You Can Raise Rent Immediately

Even if the tenant is paying below market, you can't just send a notice on day one. You inherit the lease terms. If it's a fixed-term lease with 10 months remaining, you're locked in for 10 months.

Month-to-month leases give you more flexibility, but many states require 30 to 60 days notice for rent increases, and some cities have rent control or just-cause eviction ordinances that limit what you can do. If the tenant holds a housing voucher, there is an added approval step for any increase, covered in analyzing a rental with Section 8 tenants in place.

Not Budgeting for Turnover

Every tenant leaves eventually. When they do, expect:

• 2 to 4 weeks of vacancy minimum
• $500 to $2,000 in turnover costs (cleaning, paint touch-ups, minor repairs)
• Marketing time and effort

If the existing tenant has been there a long time, the unit may also need more work at turnover than a short tenancy would. Build this into your long-term projections.

Running Your Own Numbers

Analyzing a duplex with an existing tenant takes more work than analyzing a vacant property. You need to verify the current rent, understand the lease terms, project the transition to market rent, and account for the risks specific to inherited tenants.

The extra diligence is worth it. Some of the best deals I've found were tenant-occupied properties where other buyers were scared off by the complexity. They'd rather buy vacant and start fresh. That's their loss.

Run your numbers using the lease terms for the remaining lease period, then model the property at market rent going forward. Be conservative on vacancy and turnover. If it still works, you might have found a deal.

The House Hack Calculator handles these scenarios well if you're planning to live in one unit. Input the existing tenant's rent for the occupied unit and your projections for when you eventually move out. It'll show you exactly what you're signing up for.