Rental Property ROI Calculator

The form your customers fill out

A live calculator, not a static quote request. Your customer enters their details and watches the number update on the spot, which is what turns a browser into a booked job.

What it calculates

Shows live monthly cash flow, cap rate and cash-on-cash return as the investor enters rent and expenses
Keeps your real multi-tab underwriting workbook: PMT on the mortgage, NOI rollup and vacancy and expense ratios
Captures each investor as a lead with the full deal, purchase price and projected return already calculated
Update rent assumptions, expense ratios or loan terms later just by asking Claude
Backtest against properties you already own so projected returns match your actual operating numbers

Why it closes more deals

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A live number closes deals

Customers who see a real estimate the second they enter their details are far likelier to book than ones told to call for a quote. The number is the hook.

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Runs your most complex spreadsheet

Multi-tab workbooks, lookup tables, tiered rates, conditional line items, the lot. If the math runs in Excel, CalcForms runs it behind a clean form.

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Update it by chatting

Prices move. Ask Claude to change a rate, add an option, or insert a step and the live form updates in seconds. No developer, no redeploy.

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Backtest before you publish

Run your last 20 real jobs through it and tune the formula until the live estimate matches what you actually charge. Ship it once it lines up.

How this form was built

No template builder and no code. One message to Claude with the CalcForms connector switched on:

✦ Claude with the CalcForms connector

Build a rental property ROI calculator from my underwriting workbook. Use the NOI tab for income minus vacancy and operating expenses, run PMT for the mortgage from the Financing tab, then output monthly cash flow, cap rate and cash-on-cash return on total cash invested.

Done. I built Rental Property ROI Calculator with your pricing and deployed it to forms.badabingapp.cc. The math runs server-side and every submission is saved with the inputs and email. Want to add a field or change a rate? Just tell me.

Build this exact form

CalcForms is a connector you add to Claude once. After that you build and edit forms just by chatting.

Add CalcForms to Claude. Open the Add custom connector dialog, name it Calcforms, and paste https://forms.badabingapp.cc. One time, about 60 seconds.
Paste the prompt below. Claude builds the form, wires in your math, and hands you a live URL.
Share it, then tweak by chatting. Put it on your site or send the link. Change a rate or add a field later just by asking.

Copy this prompt into Claude

"Build a rental property ROI calculator from my underwriting workbook. Use the NOI tab for income minus vacancy and operating expenses, run PMT for the mortgage from the Financing tab, then output monthly cash flow, cap rate and cash-on-cash return on total cash invested."

Example run: An investor enters a 275,000 dollar property, 25 percent down, 2,400 dollars rent and 650 dollars expenses at 7 percent. The form shows roughly 9.6 percent cash-on-cash and a 6.1 percent cap rate, then sends you the lead with the full underwrite.

New to connectors? A connector (an MCP server) is a secure link between Claude and an app. The CalcForms connector lets Claude build, deploy, and update real calculator forms for you, all from the chat window.

Formulas it supports

Effective gross income: (monthly_rent * 12) * (1 - vacancy_rate)
Net operating income: effective_gross_income - (operating_expenses * 12)
Annual debt service: PMT(rate/12, 360, -(price * (1 - down_pct/100))) * 12
Cap rate: NOI / purchase_price
Cash-on-cash: (NOI - annual_debt_service) / (down_payment + closing_costs)

FAQ

Does it calculate cap rate and cash-on-cash, not just cash flow?

Yes. It returns monthly cash flow, cap rate on NOI and cash-on-cash return on total cash invested, so investors see the full picture before they reach out.

Can it use my vacancy and expense ratios?

Yes. Your underwriting tabs carry over, so vacancy, management and maintenance ratios apply exactly as they do in your own spreadsheet, with results updating live.

Can I adjust assumptions as the market shifts?

Ask Claude to change rent comps, expense ratios or loan terms and the live calculator updates immediately, no rebuild needed.

Build yours in the next 10 minutes.

Your first form is free. No credit card.

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