DoorMeter guide
How to read the card, how every number is calculated, and how to get the most out of DoorMeter.
Getting started
- Add DoorMeter to Chrome from the Chrome Web Store, then pin it: click the puzzle piece in Chrome's toolbar and the pin next to DoorMeter.
- Open a home for sale on Zillow or Redfin. The DoorMeter card appears on the right side of the listing. Drag it anywhere; it remembers where you put it.
- Set your interest rate. Click the DoorMeter button in the toolbar and enter the rate your lender quoted. Until you do, DoorMeter uses 7%.
Works in desktop Chrome on U.S. homes for sale. Rentals, sold homes and listings without an asking price ask you to enter a price.
Reading the card
The score (0–100) sums up how close the deal comes to your targets: 70+ GOOD 40–69 FAIR under 40 WEAK
The four numbers are monthly cash flow, cash-on-cash return, cap rate and DSCR. Each is explained in How the numbers work.
The collapse button in the corner folds the card into a small pill; click the pill to open it again.
- Summary
- The monthly math, top to bottom: rent, vacancy, operating expenses, net operating income, mortgage, cash flow. Below it, the 1% rule and 50% rule checks, break-even rent and the cash you'd need to buy.
- Assumptions
- Every input you can change: price, rent, units, tax, insurance, HOA, down payment, rate, loan term, closing costs, vacancy, maintenance, CapEx and management. The numbers update when you leave a field or press Enter.
- Expenses
- Each monthly expense on its own line, and what share of the rent they take.
- Offer Pro
- The highest price that still meets each of your targets (cash-on-cash, cash flow per door, DSCR), compared with the list price.
- What-if Pro
- Monthly cash flow across interest rates (±2%) and rents (±15%). Red loses money, amber is under $100, green is $100–199, dark green is $200 or more.
- 30-yr Pro
- Cash flow, equity and the return if you sold (IRR) in years 5, 10 and 30, plus the yearly depreciation deduction.
How the numbers work
All amounts are monthly unless a formula says × 12.
| Gross rent | rent per unit × units |
|---|---|
| Effective income | gross rent × (1 − vacancy) |
| Operating expenses | tax + insurance + HOA + utilities + other + maintenance and CapEx (% of gross rent) + management (% of effective income) |
| Net operating income (NOI) | effective income − operating expenses |
| Mortgage | principal and interest on price × (1 − down payment), plus PMI of 0.5% a year when you put down less than 20% |
| Cash flow | NOI − mortgage |
| Cash needed | down payment + closing costs + upfront repairs |
| Cash-on-cash return | cash flow × 12 ÷ cash needed |
| Cap rate | NOI × 12 ÷ price |
| DSCR | NOI ÷ mortgage payment (lenders usually want 1.25 or more) |
| 1% rule | gross rent ÷ price; passes at 1% or more |
| 50% rule | operating expenses ÷ gross rent; passes at 50% or less |
| Break-even rent | the rent at which cash flow is exactly $0 |
The deal score
Each of four results is compared with your target and capped at 100%, then weighted:
- Cash-on-cash vs 8% 35
- Cash flow per door vs $200 30
- DSCR vs 1.25 20
- Cap rate vs 6% 15
With Pro, change the targets in your profile (dashboard → Profiles → "Targets (buy box)"). An all-cash purchase gets full marks for DSCR.
Where the estimates come from
Every number on the card has a chip that says where it came from. Click the chip to see the details.
PAGE read from the listing ESTIMATE filled in by DoorMeter YOU typed by you
- Rent
- The listing's own rent estimate when Zillow shows one for a single home. Otherwise HUD's Small Area Fair Market Rent for the ZIP code and bedroom count (FY2027), or the county figure when the ZIP has none. HUD rents run conservative, so a real rent comp may be higher.
- Property tax
- The county's effective tax rate × purchase price (Census American Community Survey, 2024), because taxes are usually reassessed after a sale. If the listing shows the seller's last tax bill, you can switch to it.
- Insurance
- The average premium rate for the ZIP code (or state) × price, from U.S. Treasury data (2022). These are homeowner policies; landlord policies often cost more.
- HOA
- From the listing. If a condo or townhouse doesn't list one, the card asks you for it.
The data ships inside the extension. DoorMeter never sends your listings or numbers anywhere.
Assumptions and profiles
DoorMeter starts every listing from your profile, a saved set of financing and operating assumptions. The default profile, "Buy & Hold (default)", uses:
| Down payment | 25% | Vacancy | 5% |
|---|---|---|---|
| Interest rate | 7% | Maintenance | 5% of rent |
| Loan term | 30 years | CapEx reserve | 5% of rent |
| Closing costs | 3% of price | Management | 8% of income |
| Rent growth | 3% a year | Appreciation | 3% a year |
- On a listing, change anything in the Assumptions tab. On the free plan those changes apply to that listing only.
- Your interest rate can be saved on any plan, from the toolbar button or the dashboard.
- With Pro, save a card's assumptions as a new profile ("Save profile"), keep as many profiles as you like (say, "Columbus duplexes" and "Condos, 10% down") and switch between them in the toolbar popup.
Search badges
On Zillow and Redfin search results, each home gets a quick estimate under its price, colored like the score. It uses your active profile. Badges never count toward the free monthly limit.
Grey badges mean the search card is missing something the math needs, and DoorMeter won't guess it: no asking price, units not listed (common on multi-family), HOA not listed (common on condos) or no local data. Open the listing for the full analysis.
Free plan: one sample badge per search page. Pro: a badge on every home. Turn badges off per site in the toolbar popup.
Saved deals, compare and alerts
- Save deal on the card keeps a listing in your dashboard (toolbar button → "Open dashboard"). Free saves 3 deals; Pro saves unlimited.
- The dashboard lists your deals with price, score, cash flow, cash-on-cash and cap rate. Filter, sort, add notes, and mark each one Watching, Offer made or Passed.
- Compare 2 to 4 deals side by side; a ★ marks the best value in each row.
- Export CSV and Print summary (PDF) Pro.
- Price-drop alerts Pro: when you see a saved home again on Zillow or Redfin, in its listing or in search results, DoorMeter notes the price. If it's a new low, you get a Chrome notification with the new cash flow and return. DoorMeter never visits listing sites on its own. Turn alerts off in dashboard → Settings.
Free, Pro and your license
- Free analyzes 5 listings a month. Reopening a listing you already analyzed this month is free, and the count resets on the 1st.
- Pro ($5/month or $49 once) removes the limits. See pricing.
- Activate: after you buy, Polar emails your license key. Click the DoorMeter toolbar button, paste the key into "License key" and press Activate.
- Two browsers: a key works on up to 2 browsers. With Chrome sync on, it follows your Google account to every Chrome you sign in to, and each one uses a slot.
- New computer: in the old browser, toolbar button → "Remove from this browser" (with sync on, this removes it from all your synced Chrome browsers), then activate on the new one. Lost access to the old one? Ask support to reset your slots.
- Manage or cancel: toolbar button → "Manage subscription" opens your Polar customer portal. Monthly Pro stays on until the end of the period you paid for. See the refund policy.
- Offline: DoorMeter checks your key about once a day. If it can't reach the license server, Pro keeps working for up to 7 days.
Troubleshooting
The card doesn't appear
Make sure you're on a single home's page (not search results), and that "Card" is on for that site in the toolbar popup. If the page loaded oddly, reload it.
The card asks me for a price
The listing has no asking price (off market, sold, auction, or a rental). Type the price you'd pay and press Analyze.
Zillow shows "Press & Hold"
That's Zillow checking for bots. Complete it and reload the page; the card will read the listing again.
A number looks wrong
Click its chip to see where it came from, then type your own number in Assumptions. If DoorMeter read the page wrong, use Report broken page at the bottom of the card. You'll see exactly what will be sent first: the page address (without anything after a ?), its structure, the listing ID, your browser version and your note, never your numbers or saved deals.
"That key is expired, refunded, or already active on too many devices"
Your key is on 2 browsers already, it has expired (for example a cancelled monthly plan), or the purchase was refunded. Remove it from a browser you don't use, or contact support.
Still stuck? Email support@doormeter.com.
DoorMeter's numbers are estimates, not financial advice. Check them with your lender, insurer and local professionals before you buy.