About Mortgage Scenarios

Compare properties, loan types, and down payments side by side. Find the best mortgage for your situation.

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Why Nobu Tools?

Nobu is my dog, and the inspiration behind these tools. Life is short, so we should spend less time on tedious tasks and more time with the ones we love.

Nobu Tools are built to save you time. Fast, private, no-nonsense utilities that just work, so you can get back to what matters.

🔒 Privacy First

Your financial data stays yours. Everything runs locally in your browser using Rust compiled to WebAssembly:

No data is ever sent to any server. Your mortgage details stay on your device
No data is logged or stored. We can't see your income, property values, or scenarios
Works completely offline. Once loaded, no internet needed
Native-speed calculations. The entire amortization engine runs in Rust/WASM for instant results

🏠 How It Works

Mortgage Scenarios is organized around properties and loan scenarios. Each property has shared details (value, taxes, insurance), and under it you create multiple loan scenarios to compare.

Property-Level Settings

These apply to all scenarios under a property: property value, tax rate, appreciation rate, home insurance, HOA, monthly rent (for rent vs buy analysis), and gross monthly income (for DTI calculation).

Scenario-Level Settings

Each loan scenario has its own: loan type (Conventional or FHA), down payment, interest rate, term, closing costs, mortgage insurance rate and type, extra monthly payments, and notes.

Key Features

📊 Amortization Engine Full month-by-month schedule with principal, interest, balance, home value, equity, and LTV tracking. Powered by Rust/WASM.

🏠 Rent vs Buy Enter your current rent to see when buying becomes cheaper. Accounts for rent increases, appreciation, equity build-up, and all ownership costs.

💰 Extra Payments Model additional principal payments. See exactly how much interest you save and how many years early you pay off the loan.

📋 DTI Ratio Enter gross monthly income to see your debt-to-income ratio. Color-coded status shows if you're in a comfortable range or approaching lender limits.

📑 Side-by-Side Comparison Compare all scenarios across all properties in one table. Monthly payment, upfront costs, equity, cash outlay, DTI, and rent vs buy break-even.

🔄 Import / Export / Share Save scenarios to JSON, import them later, or generate a share URL to send your comparison to someone else.

🧮 Calculation Details

The WASM engine handles all financial calculations with full precision:

Monthly payment: Standard amortization formula — P × r(1+r)ⁿ / ((1+r)ⁿ − 1)
PMI removal: Auto-terminates when balance reaches 78% of original purchase price (per the Homeowners Protection Act)
FHA MIP duration: ≥10% down = 11 years (132 payments); <10% down = life of loan
FHA UFMIP: 1.75% of base loan, optionally financed into the loan or added to closing costs
Home appreciation: Compound monthly from annual rate — recalculates property taxes annually based on appreciated value
Rent vs buy: Monthly comparison of cumulative rent (with annual increases) vs net buying cost (all payments minus equity). Break-even is when net buying cost falls below cumulative rent.
DTI ratio: Front-end housing ratio = (P&I + taxes + insurance + MI + HOA) / gross monthly income
Extra payments: Applied to principal each month (capped to remaining balance), reducing total interest and payoff timeline

💡 Use Cases

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First-Time Buyer

Compare Conventional vs FHA side by side. See how 3.5% down FHA compares to 10% down Conventional — including UFMIP, PMI differences, and when each one drops off.

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Rate & Term Comparison

15-year vs 30-year on the same property. Higher monthly payment but dramatically less interest? See the exact numbers and break-even points.

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Comparing Properties

Looking at two or three different homes? Create a property for each one with the correct value, taxes, and HOA. Add your preferred loan scenarios under each. The comparison table shows them all.

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Rent vs Buy Decision

Enter your current rent and see the break-even point. Factor in rent increases, home appreciation, and all the hidden costs of ownership to make an informed decision.

❓ FAQ

Is my financial data safe?

Absolutely. Nothing leaves your browser. There are no analytics, no tracking, no server calls. The entire calculator runs in WebAssembly on your device. You can verify by disconnecting from the internet — it still works.

How accurate are the calculations?

The amortization formula, FHA MIP rules, and PMI auto-termination thresholds match industry standards. Property taxes are recalculated annually based on appreciated home value. That said, this is an estimation tool — actual lender terms, local taxes, and insurance rates will vary.

Can I save my scenarios?

Yes — use Export to save a JSON file, Import to load it back, or Share to generate a URL that encodes all your scenarios. The share URL works for anyone — no account needed.

What does the DTI ratio mean?

Debt-to-income ratio is your total monthly housing costs divided by your gross monthly income. Lenders typically want this below 43%, and below 36% is considered strong. The tool color-codes it: green (<28%), blue (28-36%), amber (36-43%), red (>43%).

How does rent vs buy work?

The tool compares your cumulative rent payments (increasing yearly) against the net cost of owning — all housing payments minus the equity you've built. The break-even month is when owning becomes cheaper than renting on a cumulative basis.

Ready to Compare?

Start with a template or build your own scenarios from scratch.

Open Mortgage Scenarios →