Balloon payment calculator
Borrow 100,000 at 6% for 60 months, pay 500 a month, and you still owe the full 100,000 at maturity, because each payment only covers the interest. See the balloon on any car note or short commercial mortgage. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Principal amount
- 100,000
- Annual rate
- 6
- Term months
- 60
- Payment
- 500
- Monthly rate
- 0.005
- Payment count
- 60
- Total installments
- 30,000
- Balloon payment
- 100,000
A balloon loan is an installment contract that does not fully amortize by the maturity date: the borrower makes regular payments for a short term, then owes a large remaining lump sum — the balloon — when the note comes due. Car notes, five-year commercial mortgages, and seller-financed real-estate contracts are often written this way so the monthly installment stays smaller than a fully amortizing payment of the same length. This balloon payment calculator takes the original principal, the annual interest rate as a percent, the term in whole months, and the regular payment amount, walks the remaining balance through every scheduled installment, and returns the lump sum still due at maturity. Zero-rate notes and interest-only payments are supported.
What a balloon payment is and how the remaining lump sum is computed
A balloon payment is the unpaid principal that remains after the scheduled installments of a short-term note have been applied. Unlike a fully amortizing auto loan or a thirty-year mortgage, the regular payment is deliberately smaller than what would retire the principal over the balloon term, so a lump sum is still due when the contract matures.
The remaining balance after n periods on a loan with principal P, periodic rate r, and payment PMT is the standard future-value identity: balloon equals P times (1+r) to the n, minus PMT times ((1+r) to the n minus one) divided by r. When r is zero the identity collapses to P minus PMT times n.
This capability uses that identity as the economic model and then walks the schedule month by month in cents so rounding matches a servicer: each period’s interest is the opening balance times the monthly rate, principal retired is the payment minus that interest, and the new balance is what is left. If a period’s payment would more than clear the remaining balance plus interest, the loan is treated as paid off and the balloon is zero.
If the payment is smaller than the period’s interest, the balance grows through negative amortization and the balloon at maturity is larger than the original principal. Interest-only notes are the boundary case: a payment equal to monthly interest leaves the balloon equal to the original principal. Typical consumer and small-commercial balloons run thirty-six, sixty, or eighty-four months; the contract accepts any positive integer term from one through six hundred so bridge notes and longer commercial lengths still compute without a second tool.
Principal must be greater than zero, the annual rate must be finite and not negative, and the regular payment must be finite and not negative.
Where a balloon payment calculator earns its keep
Borrowers use a balloon payment calculator before signing a five- or seven-year commercial mortgage that amortizes as if it were thirty years: the monthly installment looks affordable, but the lump sum due at the balloon date is the number that actually decides whether a refinance or sale must happen on time.
Auto dealers and credit unions quote balloon or residual notes on cars so the installment undercuts a fully amortizing sixty-month payment; putting the contracted payment next to principal, rate, and term shows the residual due at maturity instead of discovering it at the desk. Seller-financed real estate often carries a three- to five-year balloon so the seller is not a bank forever; both parties can pin the same remaining lump sum from the same four fields. Failed validation, including a negative rate, does not consume balance.
What you can do with it
Five-year commercial balloon mortgage
Turn principal, quoted rate, a 60-month balloon term, and the payment sized off a longer amortization into the lump sum that must be refinanced or paid at maturity.
Seller-financed real estate
Pin the balloon a private note still owes after three to five years of installments so buyer and seller share one maturity number before closing.
FAQ
What happens if the interest rate is negative?
A negative rate is rejected and is not billed.
Does a 0% annual rate work?
The balloon is principal minus payment times the number of months, floored at zero if the installments would retire the note early.
What happens if my payment only covers the interest?
Then the balance never falls and the balloon equals the original principal. In the example, 500 a month on 100,000 at 6% is exactly the monthly interest, so 30,000 in payments still leaves 100,000 due.
Can the balloon be larger than the amount I borrowed?
Yes. If the regular payment is smaller than the month's interest, the unpaid interest is added to the balance, which grows instead of shrinking, so the lump sum at maturity exceeds the original principal.
Which term should I enter for a balloon loan?
The number of months until the lump sum is due, not a longer period the lender may have used to size the payment. A five-year balloon is 60 months, whatever period was used to set the installment.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/fin/balloon-payment \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"principal":100000,"annual_rate":6,"term_months":60,"payment":500}'const res = await fetch("https://api.kit.forhosting.com/fin/balloon-payment", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"principal": 100000,
"annual_rate": 6,
"term_months": 60,
"payment": 500
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/fin/balloon-payment",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"principal": 100000,
"annual_rate": 6,
"term_months": 60,
"payment": 500
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/fin/balloon-payment", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"principal":100000,"annual_rate":6,"term_months":60,"payment":500}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"principal":100000,"annual_rate":6,"term_months":60,"payment":500}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/fin/balloon-payment", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"principal": 100000,
"annual_rate": 6,
"term_months": 60,
"payment": 500
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "fin.balloon_payment",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
A negative interest rate is rejected with invalid_input and is not billed.
Input contract, response shape, and error behaviour
POST a JSON body with four required fields. principal is the amount borrowed, not a later payoff quote unless you are re-running the calculator on a remaining balance you already know. annual_rate is the nominal annual interest rate as a percent (six means 6 percent a year); aliases interest_rate, rate, and apr are accepted so origination forms can reuse their column names. A negative annual_rate fails with invalid_input naming the field — interest cannot be a negative percent in this contract — and that failure is not billed. term_months is the balloon term in whole months until the lump sum is due; aliases term and months map to the same field. It must be a positive integer from 1 to 600: zero, negatives, and values such as 60.5 fail with invalid_input. payment is the regular monthly installment in the same currency as principal, not a count of how many payments have been sent; aliases payments_made, monthly_payment, and pmt are accepted. Each numeric field may arrive as a JSON number or a numeric string; missing fields, empty strings, and non-finite values fail with a message that names the field. On success the body echoes principal, annual_rate, term_months, and payment, reports monthly_rate and payment_count, then the money summary: total_installments (the sum of regular payments actually applied), balloon_payment (the remaining lump sum due at maturity), total_due (installments plus balloon), and total_interest (total_due minus principal). Example: one hundred thousand at 6 percent for sixty months with a five-hundred payment is an interest-only note, so balloon_payment equals the original principal. Pair the JSON with your own amortization chart if you need every row; this endpoint returns the maturity lump sum and totals, not a sixty-line table, so responses stay small for widgets and APIs.
Where a balloon payment calculator earns its keep
Keep term_months a positive integer, pin the rounded currency fields in tests, and you get a reproducible maturity lump sum for deal jackets, education pages, and edge workers without standing up a loan-servicing stack of your own.
Integration use cases
Auto balloon or residual notes
Compare a balloon car note with a fully amortizing term: same principal and rate, smaller monthly payment, explicit residual due when the contract ends.
Technical questions
How is the balloon payment at loan maturity calculated?
The monthly rate r is annual_rate/100/12 and n is term_months. Remaining balance is P·(1+r)^n − payment·((1+r)^n−1)/r when r>0, or P − payment·n when r=0. The schedule is then walked in cents so balloon_payment is the balance still open after the installments.
What if the regular payment is interest-only?
When payment equals monthly interest, principal is not retired and balloon_payment equals the original principal (for example 100000 at 6% for 60 months with payment 500).
What does the balloon payment calculator cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input, including a negative rate, is not billed.