Custom AI Assistant: Build a Portfolio Hold-vs-Sell Advisor in Claude

What This Builds

Every quarter, or every time a lender calls with a refinance rate, you rebuild the same comparison: which property is pulling its weight and which one is quietly dragging down the portfolio. This build gives you a standing Claude Project loaded with each property's numbers and your own hold criteria, so instead of rebuilding a spreadsheet from scratch you just ask it to rank the portfolio and explain why.

Prerequisites

• Pro subscription ($20/month): claude.ai
• Your current per-property numbers: purchase price, current mortgage balance, monthly cash flow, equity, and your estimate of current value for each property
• Your own hold-versus-sell criteria written down (minimum cash-on-cash return, appreciation expectations, how much hassle you're willing to tolerate per unit)
• 60-90 minutes for initial setup, plus a few minutes each quarter to refresh the numbers

The Concept

A Claude Project is a dedicated workspace that keeps a set of documents on hand for every conversation you have inside it. Feed it your per-property numbers once, and every time you ask it something, it already has the whole portfolio in front of it. Think of it less like a chatbot and more like a standing spreadsheet you can talk to. You don't rebuild the comparison every quarter. You just ask the question again with updated numbers.

The hold-versus-sell decision usually stalls because pulling all eight or twelve properties into one comparable view takes an evening you don't have. A Project removes that setup cost every single time, so you actually run the comparison when it matters, not just once a year.

Build It Step by Step

Part 1: Create the Project

Go to claude.ai, hover the left sidebar, and click Projects (or navigate directly to the projects section). Click New Project in the upper right.

Name it something specific: "Portfolio Hold-vs-Sell Advisor." In the description field, note what it's for: "Tracks per-property cash flow, equity, and my hold criteria so I can ask which properties to sell." Claude does not read this description as instructions, so don't rely on it for behavior.

Part 2: Load Your Portfolio Data

On the project's main page, find the project knowledge panel and click the + button to add content. Upload or paste one document per the structure below rather than one giant file. Claude uses everything you add here as context in every chat inside the project.

Document 1: Property Snapshot (one row per property)

Property: [address or nickname, e.g. "Maple St Duplex"]
Purchase price: [purchase price]
Purchase date: [month/year]
Current estimated value: [your best estimate]
Current mortgage balance: [remaining balance]
Monthly rent (all units combined): [total monthly rent]
Monthly operating expenses (taxes, insurance, maintenance reserve, management): [total]
Monthly mortgage payment: [P&I plus escrow]
Known upcoming capital needs (roof, HVAC, etc.): [list or "none known"]

Repeat this block for every property in your portfolio.

Caution: these snapshots hold your most sensitive numbers day to day. Leave loan account numbers, routing numbers, and your Social Security number out of every snapshot entirely. Purchase price, rent, and mortgage balance as round figures are fine. Before you load real numbers, open Claude's data retention settings for your plan and confirm what happens to project knowledge if you ever delete the project.

Document 2: Your Hold-vs-Sell Criteria

Minimum acceptable cash-on-cash return before I consider selling: [your threshold, e.g. "6 percent"]
Appreciation assumption I use for this market: [your assumption]
How I weigh hassle (tenant turnover frequency, deferred maintenance, distance from home): [describe in your own words]
Tax situation to keep in mind (depreciation recapture, 1031 timeline, current basis): [describe generally, do not paste your actual return]
What would make me sell even a cash-flowing property: [your own rule, e.g. "equity over a set percentage of net worth in one property"]

Part 3: Set Project Instructions

Click Set project instructions and paste something close to this:

You are helping me evaluate my rental portfolio for hold-versus-sell decisions.
Use the property snapshot documents in this project as your data source.
When I ask you to rank properties, calculate cash-on-cash return and equity
position for each one using the numbers provided, and explain your ranking
in plain language, not just a table. Flag any property where the numbers
look stale (I haven't updated it in a while) and ask me to confirm current
figures before relying on the ranking. Never recommend a specific tax move.
Tell me to confirm anything involving depreciation, 1031 timing, or capital
gains with my CPA by name.

Click Save instructions.

Part 4: Test and Refine

Start a new chat inside the project and ask: "Rank my properties by cash-on-cash return and equity growth, and tell me which one is dragging down the portfolio average." Check the math against one property by hand. If Claude's numbers are off, it's almost always because a figure in your snapshot document was ambiguous. Tighten the wording and re-upload.

Real Example: The Quarterly Check-In

Setup: An eight-property portfolio is loaded into the Project, one snapshot block per property, updated every quarter.

Input: "Rank all eight properties by cash-on-cash return and equity growth. Tell me the weakest one and why."

Output: Claude ranks the eight, flags the two-bedroom on Elm Street as the weakest performer (below the stated minimum cash-on-cash return, flat equity growth over two years, and a roof replacement noted as an upcoming capital need), and lays out the case for selling versus refinancing it in three short paragraphs, referencing the reader's own stated criteria rather than generic investing advice.

Time saved: What used to mean an evening rebuilding a comparison spreadsheet from bank statements and old notes now takes the time it takes to type one question, once the numbers are current.

What to Do When It Breaks

• Claude's ranking looks wrong → Check the property snapshot documents first. A pasted figure that's a year stale will throw off every calculation downstream of it. Update the document, not just the chat message.
• Claude starts giving generic real estate advice instead of using your data → Start the message with "Using the property snapshots in this project," which nudges it back to your uploaded numbers instead of general knowledge.
• You forgot to update the numbers and don't realize it → This is the failure you won't notice on your own. Set a recurring calendar reminder for the first week of each quarter labeled "Update Claude Project property snapshots," separate from any bookkeeping reminder, so a stale ranking doesn't quietly become the basis for a real decision.
• The project knowledge feels full or sluggish → On a paid plan, Claude expands capacity automatically once you're near the limit. If responses still feel off, trim old capital-needs notes that are no longer relevant.

Variations

• Simpler version: Skip the separate criteria document and just restate your hold thresholds in the chat each time you ask. It costs you a sentence of typing but nothing to maintain.
• Extended version: Add a running log document where you paste each quarter's ranking output. Over a year, this becomes a written record of how each property trended, useful on its own when you eventually do sell and need to explain your reasoning to a lender or a future buyer.

What to Do Next

• This week: Build the property snapshot document for your three or four largest properties first and test the ranking prompt.
• This month: Fill in the rest of the portfolio and set the quarterly update reminder.
• Advanced: Ask Claude to model a hypothetical sale, refinance, or 1031 exchange scenario against the same data. Take that output to your CPA as a starting point for the real conversation, not a substitute for it.

Advanced guide for real estate investor professionals. These techniques use more sophisticated AI features that may require paid subscriptions.