Calculator Documentation
House Hacking Calculator
Live in one unit, rent the rest: see your true monthly housing cost
Schema version 1.0.0 · Category: investment
Inputs
Property & Loan
The multi-unit you would buy
| Field | Type | Default | Notes |
|---|---|---|---|
| Purchase Price | currency | $500,000 | Owner-occupied 2-4 units qualify for FHA/conventional low-down loans |
| Number of Units | select | 2 | You live in one, rent the others |
| Down Payment | percentage | 3.50% | FHA allows 3.5% down on owner-occupied 2-4 units |
| Interest Rate | percentage | 6.50% | Owner-occupied rate (better than investor rates) |
| Loan Term | select | 30 | Length of the mortgage |
Rental Income
What the other units rent for
| Field | Type | Default | Notes |
|---|---|---|---|
| Monthly Rent per Unit | currency | $1,600 | Average market rent for each rented unit |
| Vacancy Allowance | percentage | 5.00% | Budget for empty months |
| Rent You Pay Today | currency | $2,200 | What you currently pay to rent (for the comparison) |
Ownership Costs
Taxes, insurance, upkeep
| Field | Type | Default | Notes |
|---|---|---|---|
| Annual Property Tax | currency | $6,000 | Annual property tax |
| Annual Insurance | currency | $2,400 | Multi-unit policies cost more than single-family |
| Maintenance | percentage | 5.00% | Percent of rental income reserved for repairs |
Calculations
Every figure this calculator produces, in evaluation order. Formulas reference input ids, parameters, and earlier calculations.
downPaymentDown payment
purchasePrice * downPaymentPercent
loanAmountLoan amount
purchasePrice - downPayment
monthlyRateMonthly rate
interestRate / 12
termMonthsTerm months
loanTerm * 12
monthlyPIMonthly P&I
(loanAmount * monthlyRate * pow(1 + monthlyRate, termMonths)) / (pow(1 + monthlyRate, termMonths) - 1)
monthlyMIMortgage insurance (FHA MIP under 10% down, PMI under 20%)
if(downPaymentPercent < 0.10, loanAmount * 0.0055 / 12, if(downPaymentPercent < 0.20, loanAmount * 0.0050 / 12, 0))
totalPITIFull monthly ownership payment
monthlyPI + monthlyMI + annualPropertyTax / 12 + annualInsurance / 12
rentedUnitsUnits producing rent (you live in one)
units - 1
grossRentalIncomeGross monthly rental income
rentPerUnit * rentedUnits
effectiveRentalIncomeRental income after vacancy and maintenance reserves
grossRentalIncome * (1 - vacancyPercent) - grossRentalIncome * maintenancePercent
effectiveHousingCostWhat YOU pay monthly after the tenants pay their share
totalPITI - effectiveRentalIncome
savingsVsRentingMonthly savings vs continuing to rent
marketRent - effectiveHousingCost
lenderIncomeCreditRental income lenders count toward qualification (75%)
grossRentalIncome * 0.75
costsMoreThanRentingFlag: hacking costs more than current rent (0 = saves money)
if(savingsVsRenting < 0, 1, 0)
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