Duplex Rental Calculator
Run a duplex both ways — as an owner-occupied house hack at 3.5% down and as a pure investment at 25% — and see the vacancy concentration a two-unit building carries.
Duplex Rental Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Owner-occupancy loan conditions and terms vary by programme.
- Tax apportionment between personal and rental use is not modelled.
- One to four unit properties are appraised on comparables, so the cap rate shown is a sanity check only.
In short: House hacking is not free housing. At 3.5% down the effective cost is 2,111.71 against a 1,650 market rent — but year-one paydown of 5,484.30 almost exactly cancels the 5,540.53 annual premium.
Formula
effective housing = payment + taxes − other unit's rent
true benefit = paydown + appreciation − cash premium
[('house hack', 'owner-occupied terms, small deposit'), ('effective cost', 'what your own housing really costs'), ('paydown', 'forced saving a renter never accumulates'), ('concentration', 'one vacancy is half your income')]
Worked Example
- Price the loan on owner-occupied or investor terms.
- Add taxes and insurance to the payment.
- Subtract the rent from the unit you do not occupy.
- Compare against what renting the same space would cost.
- Add paydown and appreciation for the true position.
A 485,000 duplex at 3.5% down borrows 468,025 at 6.25%: 2,881.71 a month, plus 780 of taxes and insurance is 3,661.71. The other unit's 1,550 leaves an effective housing cost of 2,111.71 — 461.71 a month MORE than renting a comparable unit at 1,650, or 5,540.53 a year. But year-one principal paydown is 5,484.30, which cancels that premium to within 56.23. Add 16,975 of appreciation and the year-one benefit is 16,918.77 on 16,975 of capital. As a pure investment at 25% down the same building needs 121,250 rather than 16,975.
Strengths & Limits Of This Model
Where this engine is strong
- Reports the honest cash comparison against renting
- Adds paydown and appreciation to reach the true position
- Quantifies the fifty per cent vacancy concentration
Where it stops
- No personal/rental tax split
- Programme terms vary
Practical Use Cases
House hacking a first purchase
Using owner-occupied terms on a two-unit building.
Comparing hack against investment
Seeing how the same building behaves both ways.
Testing the honest cash position
Checking whether it really beats renting.
Sizing reserves
Accounting for fifty per cent vacancy concentration.
Planning a move-out
Modelling the transition to a full rental.
Methodology & Editorial Standards
The owner-occupied case reports the effective housing cost as payment plus taxes and insurance less the rent from the unit not occupied, then compares it honestly against renting a comparable unit rather than assuming the arrangement is free. Principal paydown and appreciation are added to reach the true year-one position, and where paydown approximately cancels the cash premium the page says so explicitly. Whichever mode is selected, the alternative is computed alongside, because the same building is a materially different deal in each.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Duplex Rental Calculator — 10 Expert FAQs
10 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
What is house hacking?
Buying a small multi-unit property, living in one unit and letting the others. The advantage is financing: owner-occupied terms on a two to four unit building allow a far smaller deposit and a better rate than any investor loan, which is the cheapest leverage most people will ever access.
Does house hacking mean free housing?
Rarely, and the claim is oversold. On an expensive duplex with a small deposit, the effective cost can exceed what renting a comparable unit would cost. The genuine benefits are principal paydown and leveraged appreciation, not a lower monthly outlay.
How much deposit do I need for a duplex?
As an owner-occupier, potentially as little as three and a half per cent through an FHA loan, or zero on a VA loan if eligible. As an investor, expect twenty to twenty-five per cent. That difference is usually far more valuable than the rate difference.
Do I have to live there?
Yes, and it is a loan condition rather than a suggestion. Owner-occupancy requirements typically run twelve months, and misrepresenting your intention is mortgage fraud. After the period ends you can normally move out and let both units.
Can the rental income help me qualify?
Usually yes. Lenders commonly count around seventy-five per cent of documented market rent from the other unit toward your qualifying income, the discount covering vacancy and management. This can substantially increase what you can borrow.
What is the biggest risk with a duplex?
Vacancy concentration. One empty unit removes half your rental income, where the same vacancy in a ten-unit building removes only ten per cent. A duplex therefore needs a deeper reserve than its modest size suggests — six months rather than three.
Is a duplex valued on income or on comparables?
One to four unit properties are appraised on comparable sales like houses, not on income like commercial multifamily. That means improving the NOI does not directly create value the way it does on a five-unit-plus building, which is a genuine structural difference.
How are taxes handled when I live in half?
You apportion between personal and rental use, typically by square footage. The rental share of mortgage interest, taxes, insurance and maintenance is deductible against rental income, and you depreciate only the rental portion of the building.
What happens when I move out?
The property becomes a full rental and both units produce income, though you lose the owner-occupied advantages on any future refinance. Many house hackers repeat the process, buying a new owner-occupied property while retaining the previous one.
Should I self-manage a duplex?
Most owner-occupiers do, since you are on site and the scale does not support a management fee comfortably. Be aware you are also the tenant's neighbour, which makes screening and clear written boundaries considerably more important than they would be at a distance.