The hidden assumption in every rent-vs-buy calculation
"You're throwing money away on rent." It's the most repeated financial advice in America, and it's wrong — or at least, deeply incomplete.
The standard argument: mortgage payments build equity, rent payments don't. Therefore buying is always better. But this ignores the single largest factor in the equation: what happens to the money you don't spend on a down payment and homeownership costs if you rent instead?
The opportunity cost of buying
A $400K home with 20% down requires $80K cash at closing. If you rent and invest that $80K at 8% returns instead, it grows to $172K in 10 years. That's $92K in pure investment gains that the homeowner doesn't have.
But the opportunity cost doesn't stop at the down payment:
- Higher monthly costs: Mortgage + property tax + insurance + maintenance + HOA typically exceeds equivalent rent. The difference, invested, compounds.
- Closing costs: 3-6% to buy, 6-8% to sell. On a $400K home, that's $12K-$24K to buy and $24K-$32K to sell — money that could be invested.
- Maintenance: The 1% rule (1% of home value per year) means $4K/year on a $400K home. Renters pay $0.
When buying wins
Buying wins when:
- You stay long enough — closing costs need 5-7+ years to amortize
- Home appreciation exceeds investment returns — rare nationally (~3-4% vs ~8-10%), but possible in specific markets
- Rent increases are high — if your area has 5%+ annual rent increases, the fixed mortgage payment becomes increasingly attractive
- You value the non-financial benefits — stability, customization, community. These are real but can't be modeled in a calculator.
When renting wins
Renting wins when:
- You might move within 5 years — closing costs destroy short-term buyers
- The price-to-rent ratio is high — in cities where a $500K condo rents for $1,800/month, the math heavily favors renting and investing the difference
- You have high investment returns — a FIRE-focused investor earning 8-10% has a high opportunity cost for tying up capital in a house
- You value flexibility — career changes, geographic moves, lifestyle shifts
The FIRE perspective
The FIRE community is split on this, and for good reason. A paid-off house dramatically reduces your FIRE expenses (no rent, no mortgage). But getting there requires years of mortgage payments that could have been invested.
The correct answer depends on your specific numbers: your market's price-to-rent ratio, your expected tenure, local appreciation rates, and your investment returns. There is no universal answer.
What most calculators get wrong
Most rent-vs-buy calculators:
- Don't model the renter's investment account — they show the buyer building equity and the renter "losing" their payment, ignoring that the renter invests the down payment and monthly difference
- Use optimistic appreciation — 5% home appreciation is above the national average
- Undercount ownership costs — many skip maintenance, HOA, PMI, or closing costs on sale
- Ignore tax complexity — the mortgage interest deduction only helps if you itemize, which fewer people do post-2018 tax reform
Run an honest comparison
The Rent vs Buy Simulator on STWLTH models both sides honestly. The renter invests the down payment and any monthly savings. The buyer builds equity and pays all real costs. Both sides invest their monthly surplus. The result shows net wealth for both paths over your time horizon — and it often surprises people.