Rent vs Buy Decider — Who's Richer in 15 Years?
"Rent is just paying someone else's mortgage" — only half true
Most comparisons stop at rent vs monthly payment. They skip the opportunity cost of the down payment, buying and selling costs, ownership costs, and the biggest variable of all: how fast prices actually grow. This tool puts both paths on the same starting line and runs them to the holding period you choose.
What you get
- Net worth comparison: buying vs renting and investing the difference, after N years.
- Three break-even lines: the year buying pulls ahead, the rent above which buying wins, and the annual price growth buying needs.
- True annual cost of owning: interest, down-payment opportunity cost, taxes, maintenance, insurance and fees, minus expected appreciation — compared directly to a year's rent.
- Sensitivity and stress tests: price growth × investment return grid, 3- to 30-year holding periods, +1 point on the mortgage rate, zero price growth, forced sale in year 5.
- Liquidity check: how many months your emergency fund lasts after buying, and what share of income ownership costs.
Who it's for
Anyone deciding whether to buy, how much to spend, or whether to keep renting a few more years. Any country and currency; defaults are clearly labeled when you skip a number.
How to use
- Download from Capafy — you get a zip file (no need to unzip).
- In Claude, turn on code execution, then upload the zip under Settings → Skills. (Claude Code users: unzip into ~/.claude/skills/.)
- Describe your situation in plain English. Claude asks for the numbers it needs, runs the model, and walks you through the results.
Output and language
Claude explains the results in your language. The Excel workbook and written report are currently labeled in Traditional Chinese; English labels are planned for a future version.
Privacy
Runs locally in your own Claude environment. No external connections, no API keys, and your numbers never leave your machine.
Requirements
A Claude environment that can run Python (e.g. Claude Code, or Claude with code execution enabled). Uses openpyxl; Claude can install it on first run.
Disclaimer
Price growth and investment returns are assumptions, not forecasts. Taxes and transaction costs follow your local rules. For reference only — not investment, tax, legal, or real-estate advice.
