Multifamily Calculator
Build the rent roll one door at a time, from a duplex up to 75 units. Underwrite the building as a hold or a value-add BRRRR, and see whether the income carries the debt.
Ideas for you
Load a Texas scenario, then make it yours. Every number updates as you type.
The building
Pencils out
$10,245 a year after vacancy, running costs, and the mortgage.
- Nets $854 a month with every cost and the mortgage covered.
- Cash-on-cash of 9.2% meets the 8% target.
- Debt coverage of 1.43x meets the 1.25x most investor lenders look for.
Cash flow goes negative once vacancy passes 22.5%, roughly 2.7 empty months a year.
Today: 6.0%. Breaking point: 22.5%.
Stress test: where it breaks
One input at a time, everything else held where you set it. The last column is where the money runs out.
| Input | Today | Breaks at |
|---|---|---|
| Rent | $5,690 | $4,545 |
| Interest rate | 7.00% | 10.99% |
| Vacancy | 6.0% | 22.5% |
| Tax & insurance | today | +61% |
Where the rent roll goes
One month, whole building.
- Rent roll (4 units)
- $5,690
- Vacancy allowance
- -$341
- Rent collected
- $5,349
- Property tax
- -$708
- Insurance
- -$383
- Repairs
- -$341
- Replacements (capex)
- -$285
- Management
- -$481
- Utilities you pay
- -$310
- Before the loan (NOI)
- $2,840
- Mortgage (principal & interest)
- -$1,986
- Monthly cash flow
- $854
What this means
Compare price per unit and rent per unit with nearby buildings, not just the bottom line. For 2 to 4 units you can use residential financing, including FHA if you’ll live in one unit. At 5 units and up, the loan is commercial and the lender sizes it on NOI.
These results are estimates for educational purposes only and do not constitute a credit decision or loan approval.
Underwriting a building, door by door
Total the rent roll, haircut it for vacancy, subtract every running cost (owner-paid utilities included), then the debt. Per-unit price and rent are your yardsticks against nearby sales.
Cash flow = Rent roll − vacancy − running costs − mortgage
- Price per unit: the price divided by the units. The quickest way to compare buildings of different sizes.
- Expense ratio: running costs as a share of collected rent. Older buildings and owner-paid utilities push it up.
- Break-even rent roll: the total monthly rent where cash flow hits zero.
A $398,000 Killeen fourplex: two units at $1,395, two at $1,450, bought with 25% down at 7%.
- Rent roll
- $5,690
- After 6% vacancy
- $5,349
- Running costs (incl. $310 utilities)
- -$2,509
- Mortgage
- -$1,986
- Monthly cash flow
- $854
An 8.6% cap rate, 9.2% cash-on-cash on $111,440 in, and 1.43x coverage at $99,500 a door. The rent roll can slide to about $4,545 before cash flow turns negative.
How Kwalifai grades a building
Hits all three targets
Cash flow every month, cash-on-cash of at least 8%, and debt coverage of at least 1.25x after running costs.
Cash flows, misses a target
It cash flows, but the return on cash is thin or the rent roll barely covers the loan.
Negative every month
Once every unit is rented and every cost is paid, the building still doesn’t cover its mortgage.
Blind spots that flatter a building
Pro forma rents
Seller rent rolls often show what rents could be. Use signed leases and verify with bank deposits.
Owner-paid utilities
Older buildings often have one water or gas meter. That bill is yours, and it grows with every tenant.
Too-low expense ratio
Small multifamily commonly runs 35% to 50% of collected rent in running costs. Much lower deserves a second look.
Assuming residential terms
At 5+ units the loan is commercial: shorter terms, balloons, and sizing on NOI rather than your income.
Multifamily questions, answered
Still unsure how a lender will see your deal? Ask Lowi AI for a scenario review.
Other investor calculators
Long-Term Rental
Hold-for-income math: true monthly cash flow, cap rate, and cash-on-cash.
BRRRR
Recycle your capital: what the refi returns and what it pays you after.
Fix & Flip
Net profit after loan, holding, and selling costs, plus your break-even sale.
Short-Term Rental
Airbnb and VRBO math with fees, turnovers, and break-even occupancy.
One building. Every unit counted.
Lowi AI can walk through FHA, conventional, DSCR, and commercial options for 2 to 75 units. No credit check to start.
These results are estimates for educational purposes only. They are not financial, investment, tax, or legal advice, and they are not a credit decision, loan approval, or commitment to lend. Verify every figure, including rents, taxes, insurance, and rehab costs, before making a decision. Kwalifai is a technology platform. Mortgage services are provided by a licensed loan originator (NMLS #2528067), licensed in Texas, enrolled with Ensure Home Loans LLC (NMLS #1666674).