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](https://www.hud.gov/topics/rental_assistance/tenantrights) first) affects your timeline, your financing options, and most importantly, whether the numbers you're running actually reflect reality.
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 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. 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 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:
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.
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:
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 actual rent from the existing lease. Then model year two and beyond at market rent, minus a reasonable vacancy factor.
Here's a framework:
| Period | Unit A (Rented) | Unit B (Vacant or Owner-Occupied) |
|---|---|---|
| Months 1-6 | Lease rent: $1,100 | Your estimate or actual |
| Months 7-12 | Market rent: $1,350 | Your estimate or actual |
| Year 2+ | Market rent with 3-5% annual increase | Market rent with 3-5% annual increase |
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:
Red flags:
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.
A Worked Example
Let's run through a real scenario.
Property Details:
Unit A (Currently Rented):
Unit B (Vacant, you'll occupy):
Monthly Expenses:
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:
That's $1,044/month average. 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.
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) + ~$8,000 (closing costs) = $65,000 > Cash-on-cash: 3,264 / 65,000 = 5.0%
That's modest, but you also lived essentially rent-free for a year relative to market rates. Factor in principal paydown (~$4,800 in year two) and you're building real wealth.
Lease Assignment: What Actually Happens at Closing
When you buy a property with an existing tenant, the lease doesn't automatically transfer. The seller needs to formally assign the lease to you, and you need to accept it.
At closing, make sure:
Some buyers skip the formal assignment and just start collecting rent. This works until there's a dispute. 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):
If you're buying as a pure investment:
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 most states require 30-60 days notice for rent increases, and some cities have rent control or just-cause eviction ordinances that limit what you can do.
Not Budgeting for Turnover
Every tenant leaves eventually. When they do, expect:
If the existing tenant is older or has been there a long time, turnover might come sooner than you expect. 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 actual 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](/tools/house-hack) 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.