Portfolio Project · Working Tool

"Everyone in the room knows the numbers. Except the buyer."

Buyer Decision
Model —
Does the math agree?

A two-mode financial tool for real estate buyers. Model the true cost of any purchase — capital lockup, opportunity cost, rent vs. buy, and market timing — in real time. Built for buyers. Shareable by anyone in the transaction.

Try the Tool → Read the Case Study ↓

Decision modes — pre-construction & resale

$10M

Price range — covers Hawaii luxury market

A–F

Dynamic grade — recalibrated per price point

Resets when switching tabs — state saves

Why this exists

I was the buyer who almost got it wrong

I was personally looking at an investment property in Hawaii. I had enough background to run the numbers and recognize the math did not work. But I kept thinking about my cousin — a lawyer — and my best friend — a bartender. Two smart, hardworking people who would have bought because an agent told them it was a good deal, and because no one ever showed them what the numbers actually said.

That is the problem this tool addresses. Not that buyers are unsophisticated. Not that anyone in the transaction is dishonest. But that there is a structural information gap in one of the largest financial decisions most people will ever make — and almost nothing exists to close it.

Everyone in the transaction has context the buyer does not. The agent knows comps. The developer knows margins. The lender knows rates. The buyer knows what they can afford and what they want. This tool gives them the one thing they are missing — what it actually costs, in their specific situation, right now.

This is the problem I am interested in: information asymmetry in high-stakes decisions. Who has the context, who does not, and what does it cost the people who do not.

Jamie Iha · on building this tool

Where buyer decisions break down

Opportunity cost of the deposit is felt but never quantified — buyers do not know what that money would earn if kept invested

Appreciation assumptions are guesses — no context for what rate a deal actually requires to break even

Rent vs. buy is treated as a lifestyle question when it is a financial one — the break-even year is almost never calculated

Market timing is driven by emotion — buyers rarely see what a rate change or price shift actually does to their monthly payment

Pre-construction and resale decisions are evaluated in isolation — no tool exists to compare both options side by side

Investment buyers and primary residence buyers are solving different problems — most tools do not distinguish between them

The Tool

Three moments that matter

The tool does three things most financial calculators do not: it gives you a grade, it explains what that grade means in plain English, and it lets you compare two real options side by side without losing your work.

Deal strength

Challenging

Financial gap is meaningful at current assumptions.

Capital locked

$150k

Cost of wait

$149k

Expected gain

$82k

Net position

-$67k

What this means

Your total cost of waiting is $149k. The home is only expected to gain $82k. You are starting $67k in the hole before you even move in.

Deal grade + plain English summary — updates as you move sliders

Comparing both options

Pre-construction

Net: -$67k
Needs: 7.2%/yr

Existing home winsBreak-even in Year 6 vs. 7.2%/yr appreciation needed to justify pre-construction.

Existing / resale

Adv: +$44k
Break-even: Yr 6

State saves when you switch tabs — your pre-construction scenario stays exactly where you left it while you explore the existing home option.

Side-by-side comparison — appears once both modes have been run

The Design

One tool, two fundamentally different decisions

Pre-construction and resale are not variations of the same question. They are different financial problems that happen to involve real estate. The tool has two modes that share common inputs but produce entirely different outputs — built around the distinct question each decision actually requires.

🏗

Is locking my capital up for months — or years — worth it compared to keeping it invested?

Models the true cost of waiting: opportunity cost on the deposit, housing costs during the wait, and whether expected appreciation justifies the commitment over a HYSA or ETF.

Capital locked + foregone investment returns

Wait cost vs. expected appreciation gain

Break-even appreciation rate

Primary residence vs. investment buyer toggle

🏡

You found the home. Does the math agree?

Answers the rent vs. buy question with actual numbers. Monthly cost comparison, break-even year, market timing sensitivity, and whether keeping the down payment invested outperforms buying.

Monthly cost to own vs. comparable rent

Break-even year — when buying beats renting

Buy now vs. wait — rate and price timing model

Buy vs. keep deposit invested chart

Design Decisions

Why it works the way it does

Every structural choice reflects a specific decision about how buyers actually think — and where financial tools typically fail them.

Score relative to price, penalized by timeline

A raw dollar threshold fails at scale — a $50k net gain means something very different on a $400k condo than a $4M penthouse. The score uses net position as a percentage of purchase price with a 1.5% penalty per year of capital lockup. At Hawaii's historical appreciation average of 3.5% over 36 months, the tool correctly grades the deal as D — not Strong.

Financial modeling

Primary residence vs. investment buyer toggle

Housing cost during the wait period is a real out-of-pocket cost for someone currently renting — but completely irrelevant for an investor who already owns. The toggle changes what factors into the score, not just the labels. Investment buyers see the slider marked optional with a checkbox to include it if relevant to their situation.

UX decision

Plain English summaries that read actual numbers

Every output section ends with a 2–3 sentence summary written from the user's specific scenario values. Not a generic description of what the chart shows. "Your total cost of waiting is $148k. The home is only expected to gain $81k in that time. You are starting $67k in the hole before you even move in." That is a sentence a buyer can act on.

UX writing

Hawaii-anchored context on every ambiguous input

Appreciation, construction timelines, cap rates — inputs that require market knowledge include helper text anchored to Hawaii data. A buyer who does not know what appreciation to expect sees "Hawaii condos have historically averaged 3–5%/yr. Use 3.5% as a conservative baseline." They get a starting point, not a blank slider with a number they have to invent.

Content strategy

State saves between tabs — nothing resets when you switch

The most common use case is a buyer evaluating two real options at the same time. If switching tabs reset the inputs, the tool would force users to re-enter their scenario from scratch — exactly the kind of friction that causes people to abandon tools halfway through. State saves automatically on tab switch and restores on return. Each tab has its own reset button so users can clear one scenario without losing the other.

Systems thinking

Scope

What this tool is — and what it is not

Clarity about scope is a design decision. The tool is explicit about its limitations because a tool that overclaims loses user trust the moment a real-world outcome diverges from the output.

What it is

✓A financial decision-support tool for buyers evaluating real estate purchases

✓A way to quantify opportunity cost, wait cost, and break-even thresholds

✓A comparison tool for buyers weighing pre-construction vs. existing options

✓A starting point for a conversation with a broker or financial advisor

✓A tool that works from $300k condos to $10M luxury properties in Hawaii

What it is not

✗Financial, investment, legal, or real estate advice

✗A mortgage qualification or affordability calculator

✗A guarantee of future appreciation, returns, or market conditions

✗A replacement for a licensed financial advisor or real estate professional

✗A model that accounts for closing costs, capital gains, or individual tax situations

Context

What this project demonstrates

This tool was built to demonstrate financial modeling, UX systems thinking, and the ability to translate complex decisions into interfaces that non-experts can actually use. The design choices — from how the score is calibrated to why each section has a plain English summary — reflect a specific point of view about where financial tools fail the people they are supposed to serve.

Nearly ten years of experience coordinating operations, finance, and strategy in commercial real estate informed the framing. The problems this tool addresses — buyers who feel the math but cannot see it, decisions made on intuition because the numbers are too abstract — are problems I have watched play out in real transactions.

Portfolio note

This is a working prototype built for portfolio purposes. It simplifies mortgage amortization, closing costs, tax obligations, HOA escalation, capital gains treatment, and individual financial circumstances. It does not constitute financial, investment, legal, or real estate advice. All outputs are estimates based on user-entered assumptions. Always consult a licensed financial advisor and real estate professional before making any real estate or investment decision.

Working Tool

Try both modes

Pre-construction and existing home scenarios are both live.

Open the Tool → ← Back to Portfolio

Buyer DecisionModel —Does the math agree?