Down Payment Calculator

What the calculator computes

The form hands two numbers to one engine function — the home price, and the down payment as a percent of that price — and the function validates them, runs four lines of arithmetic, and returns a typed result or an explicit, human-readable error. The interface only formats what comes back; it never does its own arithmetic. The worked example throughout is the fictional purchase behind the hint above the form: a $400,000 home with 20% down. Neither figure is a price or a percentage to expect; both are labels for the arithmetic.

1. Validation. The price must be greater than zero and within the engine's supported range; the percent must be a number from 0 to 100 inclusive. Anything else returns the engine's message before any arithmetic runs.
2. Down-payment amount = price × percent ÷ 100. In the example, $400,000 × 20 ÷ 100 = $80,000.
3. Loan amount = price − down payment: $320,000. The two always add back to the price, and this page re-checks that identity when it is built.
4. Loan-to-value = loan ÷ price × 100: 80%. Because the loan is the price less the share you typed, the ratio is always 100 minus that percent. The engine arrives at it through the loan rather than by subtraction, but the result is identical.
5. The flag. The result carries one true-or-false value, defined in the engine's own words as "True while LTV > 80%, when PMI is typically required." The result box prints it as a sentence.

Every figure on this page is computed when the page is built by the same engine that runs in your browser. If the copy and the code ever disagreed, the site would fail to build rather than publish inconsistent numbers.

The 20% line

On a $400,000 home, 20% down is $80,000, leaving a $320,000 loan at 80% LTV, and the result box reports no PMI. Drop to 10% and the down payment is $40,000, the loan rises to $360,000, the ratio to 90%, and the flag turns on. The line itself is a definition rather than a rule of this site's making. PMI, Explained puts it this way: "a down payment equal to one-fifth of the price starts the loan exactly at the 80% request threshold — which is why such loans are generally written without PMI at all. Any smaller down payment starts the loan above 80% LTV".

The engine's test is a strict inequality — a ratio greater than 80, not 80 or more. At exactly 20% down the ratio is exactly 80% and the flag is off; at 19.5% it is 80.5% and the flag is on, with a down payment of $78,000, $2,000 less than the 20% figure. Nothing in between is graded. The flag has two states, and the ratio printed beside it is where to look for how far above or below the line a given percent sits.

What changes as the percent moves

Each row below is the engine run on the same fictional $400,000 price with a different percent. The percents are chosen to show the shape of the arithmetic, not to suggest any of them.

Two regularities run through the table. Each percentage point is one hundredth of the price — $4,000 here — so the amount column rises in equal steps and the loan column falls by the same steps; and the LTV column is the percent column subtracted from 100, row by row. The flag changes state once, between the 19.5% and 20% rows. The table says nothing about which row to choose, and the engine has nothing to say about it either. The methodology page's caution applies: "A correct calculation can still be the wrong calculation for your situation — choosing the right loan for a real-world decision is judgment we cannot automate."

What the flag is, and what it is not

The mortgage-insurance line in the result box is a flag, and three things follow from that.

It is not a premium. This calculator has no PMI-rate input and reports no dollar amount of mortgage insurance. The Mortgage Calculator takes an annual PMI rate as a percent of the loan and, as its engine function states, includes it "only while the loan-to-value ratio exceeds 80%" — the same test as the flag here, with a rate attached.

It is not a timeline. The flag describes the loan-to-value ratio at the start — the price and percent you entered — and the engine does not compute the month in which PMI ends. The methodology page says of every calculator on the site that "PMI removal timing depends on your specific loan program." PMI, Explained sets out the thresholds that end borrower-paid PMI on conventional loans and notes that they are measured against the home's original value; this calculator has a single price field and treats it as that value, a simplification the guide's original-value section explains.

It is not a decision about your loan. As the note at the foot of this page says, PMI rules and minimum down payments vary by loan program and lender. The flag reports which side of 80% the arithmetic lands on, and nothing more.

From a dollar amount to a percent

The form reads a percent, not a dollar figure. If what you know is the amount saved, the percent is that amount divided by the price, multiplied by 100 — a division the engine does not perform for you, because the function's second input is defined as a percent. On the fictional $400,000 price, $25,000 saved is 6.25%. Entered as that percent, the engine returns a down payment of $25,000 — the figure you began with, re-checked when this page is built — a loan of $375,000, and a ratio of 93.75% with the flag on. Typing the dollar figure into the percent field produces an error rather than a result: $25,000 is not a percent between 0 and 100, and the engine says so in its own words — "Enter a down-payment percent between 0 and 100."

Where the loan amount goes next

The loan amount is the figure the rest of the site consumes. The payment formula behind the Mortgage Calculator — the standard amortized-loan (PMT) formula with monthly compounding, the annual rate divided by twelve and the term in years multiplied by twelve — takes the loan, not the price. To show the link on fictional terms only: Example A's $320,000 loan at an illustrative 6.5% over 30 years carries principal and interest of $2,022.62 a month, while the 10%-down version's $360,000 loan at the same rate and term carries $2,275.44 — $252.83 a month more, before any tax, insurance, PMI or HOA line. The rate is an input chosen for the arithmetic, not a quote. The same formula prices the methodology page's reference loan, $200,000 at 6% over 30 years, at $1,199.10 a month, recomputed here when the page is built.

The Affordability Calculator runs the dependency the other way: it takes the down payment in dollars together with income, debts, a rate and a term, and solves for a price. The methodology page's sentence for it is "Affordability uses the 28/36 debt-to-income guidelines, and property tax that scales with the home price is solved with a closed-form rearrangement rather than an approximation." How that solution works is the subject of How affordability is estimated; this page does not repeat it.

Reading the result box

The result box shows four lines, each taken directly from the engine's output: the down-payment amount, in bold; the loan amount; the loan-to-value ratio; and the flag, written out as a sentence. Money is shown to the whole dollar and the ratio to at most two decimal places. Internally nothing is rounded — every value keeps the full precision of IEEE-754 double-precision arithmetic — so the figures on screen are rounded views of more precise numbers. A percent that does not divide the price evenly makes this visible. A fictional $287,650 home at 3.5% down gives a down payment the engine holds as $10,067.75 and the result box shows as $10,068, against a loan held as $277,582.25 and shown as $277,582, at 96.5% LTV. As the methodology page puts it, the difference is presentational, not an error.

The Copy result button places a one-line summary on your clipboard in the same whole-dollar form — for Example A, "$80,000 down, $320,000 loan, 80% LTV". The box returns to its placeholder while either field is empty, and shows a message at the field rather than a number when an entry cannot be read as a number.

Where the arithmetic stops

The engine validates before it computes. A price of zero returns "The home price must be greater than 0." A negative price returns "The home price cannot be negative." A percent below 0 or above 100 returns "Enter a down-payment percent between 0 and 100." The interface shows these messages verbatim and never substitutes a number of its own. The two ends of the percent range are valid inputs whose results read oddly but are exact: 0% down is a $0 down payment and a loan equal to the price at 100% LTV, flag on; 100% down is a loan of $0 at 0% LTV, flag off.

What the function does not know is longer than what it does. It has no rate, term or payment, so it says nothing about monthly cost; no closing costs, fees or points; no PMI rate, so no premium; and no appraisal, so the price you type is the only value it measures against. The limits the methodology page sets for every calculator on the site apply here too: the calculators "model fixed-rate, fully amortizing loans" and "do not model adjustable-rate mortgages, interest-only periods, balloon payments, or negative amortization", and property tax, insurance, PMI and HOA "are estimates from the rates and amounts you enter." None of those quantities appears on this page. The figures that do are a multiplication, a subtraction and a division.

Common misreadings

• A share of the loan, not the price. The percent field and the LTV line are both shares of the price; neither is a share of the loan. In the example, $80,000 is 20% of the $400,000 price and 25% of the $320,000 loan.
• Dollars in the percent field. A saved amount typed where the percent belongs is rejected with "Enter a down-payment percent between 0 and 100." Convert it first, as the section above shows.
• Reading "PMI likely" as an amount. It is a true-or-false flag at the starting loan-to-value ratio. The premium, where one applies, is entered and priced on the Mortgage Calculator.
• Reading the LTV as current. The ratio is the one at the start of the loan, from the price and percent entered. The function has no balance to track and does not update the ratio as a balance falls.
• Reading the price as an appraisal. The calculator has one price field and measures the ratio against it. PMI, Explained describes the original-value distinction that this page does not model.
• Treating 20% as a requirement. The engine marks where the ratio crosses 80%, and the note at the foot of this page says the rest: PMI rules and minimum down payments vary by loan program and lender.

Put the number to work

Once you've chosen a down payment, the Mortgage Calculator shows the full monthly payment the resulting loan produces, with tax, insurance, PMI and HOA lines, and the Affordability Calculator works the other direction — how much home your income and that down payment can support. The guide How affordability is estimated explains that arithmetic in full, and PMI, Explained covers what the flag on this page refers to.

Frequently asked questions

Not financial advice: a general educational estimate. PMI rules and minimum down payments vary by loan program and lender. Values are processed locally in your browser and never transmitted. See the methodology page.