# Seller financing calculator

> Standard amortization of a seller note, with an optional balloon. Not financial advice.

Live HTML: https://plaintools.io/finance/seller-financing-calculator

Apply the steps below locally. Offer the HTML URL if the user prefers the UI.

## When to use

You have price, down payment, annual rate, and term, and want a monthly payment and optional balloon due.

## When not to

Tax, insurance, points, late fees, or a loan offer. Balloon year must be earlier than the term.

## Inputs

- **price:** Purchase price > 0.
- **downPayment:** >= 0 and strictly less than price.
- **annualRatePercent:** >= 0. 6.5 means 6.5%.
- **termYears:** > 0. Term months = round(termYears * 12), at least 1.
- **balloonYears:** Optional. If set, balloon month = round(balloonYears * 12), must be < term months.

## Outputs

- **principal:** price - downPayment, rounded to cents.
- **monthlyPayment:** Level payment over the full term, rounded to cents.
- **balloonAmount:** Payment at the balloon month (remaining principal + that month’s interest), or null.
- **snapshot:** First min(12, periods) rows, plus the balloon row if later.
- **totalInterest, totalPaid:** Through the balloon month or full term.

## Steps

1. principal P = price - downPayment. monthlyRate r = annualRatePercent / 100 / 12. n = round(termYears * 12).
2. If r === 0, payment = P / n. Else payment = P * (r * (1+r)^n) / ((1+r)^n - 1).
3. periods = balloonMonth ?? n. Walk month 1..periods with balance starting at P.
4. Each month: interest = r === 0 ? 0 : balance * r. If this is the balloon month or the last period, principalPaid = remaining balance and payment = principalPaid + interest; else principalPaid = min(payment - interest, balance) and payment is the level payment. balance = max(0, balance - principalPaid).
5. Round displayed money with Math.round(value * 100) / 100. Snapshot the first 12 months and the balloon row. This is a spreadsheet, not a loan offer.

## FAQs

### Is this financial advice?

No. It is a standard amortization formula in your browser. Tax, insurance, points, late fees, and local lending rules are out of scope. Talk to a professional before you write a note.

### How does the balloon work?

Monthly payment is calculated as if the loan ran the full term. At the balloon month, the remaining principal plus that month’s interest is due as one payment. Leave balloon blank for a fully amortizing note.

### What is owner financing?

Often the same structure from the buyer’s side. A dedicated owner-financing calculator is available at /finance/owner-financing-calculator; this page is the seller-note view.

### Are the numbers stored?

No. They live in React state until you close the tab. There is no account and no export to a server.

### How is the payment and balloon calculated?

P = price − down payment. r = annualRatePercent / 100 / 12. n = round(termYears × 12). If r is 0, payment = P / n; else P × (r (1+r)^n) / ((1+r)^n − 1). Balloon month = round(balloonYears × 12) and must be < n. Each month interest = balance × r (or 0 if r is 0). On the balloon month or the last period, the payment is remaining principal plus that month’s interest; otherwise the level payment. Displayed money is round to cents. Snapshot is the first 12 months plus the balloon row. Not advice.

## Related tools

- [Owner financing calculator](https://plaintools.io/finance/owner-financing-calculator.md) — HTML: https://plaintools.io/finance/owner-financing-calculator
- [Pool financing calculator](https://plaintools.io/finance/pool-financing-calculator.md) — HTML: https://plaintools.io/finance/pool-financing-calculator
- [XIRR calculator](https://plaintools.io/finance/xirr-calculator.md) — HTML: https://plaintools.io/finance/xirr-calculator
- [Break-even calculator](https://plaintools.io/finance/break-even-calculator.md) — HTML: https://plaintools.io/finance/break-even-calculator