This calculator adds your target down payment to a flat 3% closing-cost estimate, then compounds your monthly savings until the balance clears that total. On a $450,000 home at 10% down with $5,000 already saved and $800 a month at a 4% return, the goal arrives in exactly 60 months. Adding $200 a month cuts that timeline further than a 2-point higher return does — contribution size, not investment return, is what moves this number.
How this calculator builds the timeline
The goal isn't just the down payment — it's the down payment plus a closing-cost estimate, because both are due in cash on the same day. The calculator sets totalCashNeeded = (home price × down payment %) + (home price × 3%), subtracts what you've already saved, and simulates your balance forward one month at a time: each month it multiplies the current balance by your expected monthly return and adds your contribution, then checks whether the running total has cleared the goal.
Run the same inputs with a 0% return instead of 4% and the payoff month moves to 67, not 60 — seven months later, funded entirely by contributions rather than growth. Run it again with monthly savings raised from $800 to $1,000 and the payoff pulls in to month 49, eleven months earlier. Doubling the return's improvement (from 4% to 6%) only pulls the date in to month 57 — three months. At this horizon, how much you contribute each month moves the answer roughly three to four times as much as how well that money is invested, which is why the FAQ's advice to prioritize a safe, liquid account for a 1–2 year goal costs you almost nothing in growth you'd have captured anyway.
What happens when the goal is unreachable
The month-by-month loop has a hard stop at 600 iterations — 50 years — so it never runs forever. That cap matters for a specific case: a saver contributing $0 a month at a 0% return never reaches any goal above their starting balance, and without a separate check the calculator would have reported "50 years to your goal" as if that were a real answer. It isn't. The tool now compares the final simulated balance to the total cash needed and reports the goal as unreachable at these inputs rather than presenting the 600-month cap as a timeline. If your result says unreachable, the fix is almost always the same lever from above: raise the monthly contribution, not the assumed return.
Why the down payment percentage matters more on an expensive home
The down payment percentage you enter does more than set the cash goal — on a pricier home it can determine what kind of loan you're even shopping for. The Federal Housing Finance Agency set the 2026 baseline conforming loan limit at $832,750 for most counties, with a high-cost-area ceiling of $1,249,125. A loan above the limit that applies in your county is a jumbo loan, which typically carries its own rate and a larger required down payment.
This calculator doesn't apply loan limits automatically — the down payment percentage is your input, not its output — but it's worth checking your target percentage against the limit for your home's price and county before you lock in a savings goal, since a jumbo threshold can change the loan program, the rate, and sometimes the minimum down payment itself.
What the 3% closing-cost estimate doesn't cover
The calculator's closing-cost line is a flat 3% of home price, applied the same way regardless of location, loan type, or lender. It's a reasonable planning midpoint, but two things it can't see:
- ·Where you're buying. Transfer taxes, attorney-involvement requirements, and title costs vary by state and even by county, and can push the real number above or below 3%.
- ·Seller or lender credits. Concessions negotiated into the purchase contract, or lender credits taken in exchange for a slightly higher rate, reduce the cash actually due at closing — but this tool has no field for them, so a generous seller market can mean your real goal is smaller than the total it shows.
Once you have a signed contract or a Loan Estimate with an actual closing-cost figure, swap it in for the 3% placeholder and re-run the timeline — the rest of the math (compounding, the monthly loop, the reachability check) works the same way against any total.
Methodology
The savings timeline is produced by simulating the calculator's own month-by-month loop: balance = balance × (1 + monthly return) + monthly contribution, checked each month against the target (down payment + a flat 3% closing-cost estimate) until it clears or the 600-month cap is hit. The conforming-loan-limit example uses the FHFA's own 2026 published figures. No figure here is estimated or interpolated beyond arithmetic performed on those two sources.
Sources
- Federal Housing Finance Agency — 2026 Conforming Loan Limit Values — accessed 2026-09-05