Model rent-vs-buy honestly — year-by-year net position for both paths including the assumption everyone drops (the renter invests the difference), with a breakeven horizon instead of a verdict. Use when asked should I rent or buy, does buying beat renting in my city, when does buying break even, or run the rent-vs-buy numbers. Produces the year-by-year comparison table, the breakeven year, the assumption list with defaults labeled, and the not-modeled list.
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Use rent-vs-buy to model [home price and comparable rent], [financing and expected stay], and [growth assumptions], producing a year-by-year comparison, breakeven horizon, labeled assumptions, and unmodeled factors; treat it as educational, not financial advice.
Required inputs
[home price and comparable rent]
[financing and expected stay]
[growth assumptions]
User-approved starter prompt based on a pinned source version; check current skill requirements before running. Task evidence ↗
SKILL.md
name: rent-vs-buydescription: "Model rent-vs-buy honestly — year-by-year net position for both paths including the assumption everyone drops (the renter invests the difference), with a breakeven horizon instead of a verdict. Use when asked should I rent or buy, does buying beat renting in my city, when does buying break even, or run the rent-vs-buy numbers. Produces the year-by-year comparison table, the breakeven year, the assumption list with defaults labeled, and the not-modeled list."
Rent vs Buy Skill
Rent-vs-buy arguments are usually two people comparing different questions: one counts equity and forgets transaction costs and carry; the other counts rent as "thrown away" and forgets the renter can invest the difference. This skill runs the symmetric model — both paths get their real costs and their real compounding — and delivers a breakeven horizon, because the honest answer is almost always "it depends how long you stay."
What This Skill Produces
The year-by-year table — owner net position (equity minus selling costs) vs renter net position (invested savings), per year
The breakeven year — before it, renting won; after it, buying won, on the stated assumptions
The assumption ledger — every input labeled, defaults flagged as defaults
The not-modeled list — taxes/deductions, renovation risk, the non-financials — stated up front
Required Inputs
Ask for these if not provided:
Home price and comparable monthly rent — same home, same neighborhood; comparing a condo rent to a house purchase is the classic apples-to-oranges error
Down payment %, mortgage rate, term (defaults 20% / 6.5% / 30yr, labeled)
How long they expect to stay — the single most decision-relevant input
Deterministic. The renter's pot starts at the down payment + closing costs (the money a buyer parts with on day one) and each year absorbs the difference between owner outflow and rent. Selling costs are applied at every horizon — equity you can't access without paying 7% isn't fully yours.
Framework: The Symmetry Rules
The renter invests the difference — the model's load-bearing assumption; a renter who spends the difference makes buying win almost automatically, and that's a behavior question, not a math question. Say so.
Carry costs are real — tax, insurance, maintenance (~2%/yr of value) never build equity; "my mortgage is like rent" omits them
Transaction costs decide short horizons — ~3% in and ~7% out is why breakeven is measured in years, not months
Appreciation is an assumption, not a birthright — vary it before trusting a conclusion; a 1-point change often moves breakeven by years
The output is a horizon, not a verdict — "buying wins if you stay past year N" is the honest deliverable
Output Format
Rent vs Buy: [scenario]
The Table and the Breakeven
[Script output: year-by-year net positions, breakeven year]
What the Breakeven Means
[Two sentences: how the user's expected stay compares to the breakeven, and which assumption the conclusion is most hostage to.]
What This Model Ignores
Taxes and deductions (jurisdiction-specific) · renovation and repair surprises · rate refinancing · the non-financials (stability, flexibility, the yard) — which are allowed to outvote the math.
Educational model, not financial advice — verify with a licensed professional before acting on it.
Quality Checks
The renter-invests-the-difference assumption is stated explicitly
Selling costs are inside the owner's net position at every horizon
The breakeven year is compared against how long the user expects to stay
At least one sensitivity note (appreciation or investment return varied)
The disclaimer line appears in the artifact
Anti-Patterns
Do not declare a universal winner — the deliverable is a breakeven horizon
Do not count rent as "thrown away" without counting interest, tax, and maintenance the same way
Do not compare non-comparable homes (rent a 1BR vs buy a 3BR)
Do not model jurisdiction-specific tax benefits — name them as unmodeled instead
Do not let the math silently overrule stated non-financial priorities — surface the tension