A FIRE Calculator for First-Time Home Buyers: What to Track

Closing on a first home is the largest single re-pricing event a FIRE plan goes through, and most calculators handle it badly. The hit is real — the median first-time buyer in 2024 put 9% down, the highest down-payment percentage since 1997^[] — but so is the inflation hedge that comes with a 30-year fixed mortgage at the prevailing 6.30% rate.^[] A FIRE calculator for first-time home buyers has to track both, or it will systematically over- or under-state how much the purchase actually delays financial independence.

The goal here is not to talk anyone into or out of a home purchase. It is to make the post-closing FIRE math visible: the down payment that left the compounding base, the principal portion of the mortgage that quietly rebuilds equity each month, and the home itself, which is an asset on the net-worth statement but not a liquid one against the 25× FIRE number.

Why a home purchase re-prices the FIRE math

The standard FIRE framework — invest 25× annual expenses, withdraw 4% in retirement^[] — assumes expenses grow with inflation. A homeowner with a 30-year fixed mortgage breaks that assumption for the largest line item on the budget. Principal and interest are fixed in nominal dollars for the life of the loan, which means the real value of the payment shrinks every year inflation is positive. Most online FIRE calculators apply a single inflation-adjusted expense series and miss this entirely.

The other half of the re-pricing is the down payment. The median first-time buyer in 2024 was 38 years old (and 40 in the 2025 NAR release) with a $97,000 household income, paying 9% on a $408,800 March 2026 median existing-home price.^[][] That is roughly $36,800 of liquid net worth converted into illiquid equity in a single transaction. At a 7% real return,^[] $36,800 compounding for 30 years would have grown to about $280,000 — the true opportunity cost of the down payment, almost never shown by either renter or homeowner calculators.

The three things to actually track after closing

The dashboard most first-time buyers need is short, not pretty. Three numbers cover almost everything:

1. Real housing cost, not the mortgage payment. Principal, interest, property tax, homeowner's insurance, HOA, and a maintenance reserve of roughly 1% of home value per year. The mortgage statement is the smallest of these.
2. Cash savings rate, computed on net-of-housing income. A first-time buyer who held a 25% pre-purchase savings rate but now spends $1,000 more per month on housing has not failed — they have simply traded a portion of liquid savings for principal paydown. The cash savings rate is what determines years-to-FI.
3. Years-to-FI under two scenarios: pay off the mortgage, or never prepay. The math diverges sharply because the prepay scenario front-loads the savings rate cliff but ends with lower lifetime expenses. Most calculators only model one path.

What a FIRE calculator for first-time home buyers should toggle

The FIRE calculator inside MFFT exposes three switches that matter for a first-time buyer. First, the down-payment input is treated as a one-time withdrawal from the investable-assets line, not as a vanishing expense — that is the only way to surface the opportunity-cost number above. Second, principal and interest can be marked as nominal-fixed, which lets the projection run with a shrinking-real-expense series for the duration of the loan. Third, the home itself can be held outside the 25× denominator while still appearing in the net-worth view, so the FIRE number stays anchored on liquid investable assets. For the cashflow companion question — categorizing closing-cost line items, mortgage escrow, and the sudden appearance of property tax as a recurring bill — the spending-side tooling is built for the same transition.

The original calculation rendered below uses NAR's 2024 median first-time buyer income and the March 2026 median home price, holding the cash savings rate at 20% of post-tax income. The result is a delay of roughly 1.8 years versus the renter trajectory — the down-payment hit dominates, and the inflation-hedge property of the fixed mortgage closes some but not all of the gap. Buyers who let lifestyle inflate into the new mortgage lose substantially more time; buyers who absorb the down payment without changing their savings rate lose less.

A common pitfall: counting the house twice

The most common FIRE math error among new homeowners is double-counting equity. The home shows up as an asset on the net-worth statement (correct), and the buyer also reduces their FIRE number by the future mortgage payoff (also defensible) — but doing both inflates progress. The clean treatment is to compute the FIRE number on liquid investable assets only, and to model the home as a separate balance-sheet line that affects net worth and post-FI expense levels but not the 25× target itself.

The second pitfall is treating the mortgage as a "guaranteed return equal to the mortgage rate." It functions that way only if the alternative is sitting in cash. Compared to a long-horizon equity portfolio at the historical 7% real return,^[] the prepay-or-invest call rarely favors prepayment unless the buyer is within five to seven years of FI and starting to dial down sequence-of-returns risk.

What I would track on day one of homeownership

The dashboard I would actually build for a first-time buyer is four numbers wide and updates monthly. The first is a liquid investable-asset number — checking, brokerage, retirement, HSA — explicitly excluding home equity. The second is a savings rate computed on net-of-housing income. The third is a years-to-FI projection built on the liquid number, with the fixed P&I treated as a shrinking-real expense for the next 30 years. The fourth is a single line that reads either "on track" or "behind plan" against a target FI age that the buyer set at the outset.

What I would not track is monthly home-equity changes from price-index updates. The number is noisy, the asset is illiquid, and obsessing over Zillow estimates is the homeowner equivalent of refreshing a brokerage app — informational at best, distracting at worst. Track the mortgage principal balance instead. It moves slowly, predictably, and in the right direction.