Summary: FirstDoor scores a rental property from 0 to 8 points using five metrics (monthly cash flow, cash-on-cash return, DSCR, cap rate and the 1% rule) and labels it Good (6–8), Okay (3–5) or Pass (0–2). All formulas are below and can be cited.
Inputs
Purchase price, down payment %, interest rate %, loan term (years), monthly rent, property tax ($/yr), insurance ($/yr), HOA ($/mo), vacancy %, maintenance %, management % (each a percent of rent) and closing costs ($).
Definitions and formulas
Loan amount
L = price × (1 − down% ÷ 100)
Monthly principal and interest (P&I)
P&I = L × r ÷ (1 − (1 + r)^−n), r = rate ÷ 12 ÷ 100, n = years × 12If the rate is 0, P&I = L ÷ n.
Monthly operating expenses
OpEx = tax ÷ 12 + insurance ÷ 12 + HOA + rent × (vacancy% + maintenance% + management%) ÷ 100
Net operating income (NOI)
NOI (monthly) = rent − OpExNOI excludes the mortgage.
Monthly cash flow
Cash flow = NOI − P&I
Cap rate
Cap rate = NOI × 12 ÷ price × 100
Cash invested
Cash invested = price × down% ÷ 100 + closing costs
Cash-on-cash return
CoC = cash flow × 12 ÷ cash invested × 100
DSCR (FirstDoor)
DSCR = NOI ÷ P&IThis is stricter than the lender-style DSCR many rental lenders use (gross rent ÷ PITIA, where PITIA = P&I + taxes + insurance + HOA). FirstDoor's calculators show both where relevant.
1% rule
Ratio = rent ÷ price × 100; passes if ≥ 1%
Scoring (0–8 points)
| Monthly cash flow ≥ $200 | 2 |
| Monthly cash flow ≥ $0 | 1 |
| Cash-on-cash ≥ 8% | 2 |
| Cash-on-cash ≥ 4% | 1 |
| DSCR ≥ 1.25 | 2 |
| DSCR ≥ 1.0 | 1 |
| Cap rate ≥ 6% | 1 |
| Passes 1% rule | 1 |
Verdict: Good = 6–8 points, Okay = 3–5, Pass = 0–2. FirstDoor also flags vacancy under 5%, maintenance under 5% and management at 0% as optimistic assumptions. The thresholds are FirstDoor's beginner rules of thumb, not industry standards.
Worked example
$200,000 price, 20% down, 7% for 30 years, $2,200 rent, $2,400/yr tax, $1,200/yr insurance, 5% vacancy, 5% maintenance, 8% management, $6,000 closing costs: P&I $1,064.48; OpEx $696; NOI $1,504/mo; cash flow +$439.52/mo; cap rate 9.02%; cash-on-cash 11.47%; DSCR 1.41; rent/price 1.10%. Score 8/8: Good.
Use it programmatically
A free JSON endpoint returns the same results: GET https://usefirstdoor.com/api/score?price=200000&rent=2200. See the OpenAPI spec and llms.txt.
How to cite
"FirstDoor deal score methodology, usefirstdoor.com/methodology (2026)." FirstDoor is an educational tool, not financial advice.