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Balloon Loan Calculator

Computes the payments of a balloon loan: the monthly payment amortized over the full amortization period, the lump-sum balance (balloon) due when the loan matures early, and the total paid and interest up to and including the balloon.

When to use

You need the monthly payment and final lump sum of a mortgage, commercial or auto loan whose payments are based on a long amortization but which must be repaid or refinanced after a shorter term.

Do not use when: The loan is fully amortized over its term (use loan-payment or amortization-schedule), or payments are interest-only before the lump sum (use interest-only-loan). Informational; not financial advice.

Formula

i = interest_rate_percent / 1200; N = 12 × amortization_years; n = 12 × balloon_after_years; monthly_payment M = P × i / (1 − (1 + i)^−N); balloon_payment = P(1 + i)^n − M((1 + i)^n − 1)/i; total_paid_before_balloon = M × n; total_interest = M × n + balloon − P; total_cost = M × n + balloon

Standard monthly amortization with end-of-month payments; the balloon equals the amortized balance after n payments and is assumed paid with the n-th payment. With a zero rate the payment is P / N and the balloon P − M × n. Lenders round payments to cents, so real balances can differ by a few cents.

Inputs

Parameter	Type	Unit	Required	Description
`loan_amount`	number		yes	Principal borrowed. Range: > 0, ≤ 1000000000000
`interest_rate_percent`	number	%	yes	Fixed nominal annual rate in percent; the monthly rate is this / 12. Range: ≥ 0, ≤ 100
`amortization_years`	number	years	default 30	Period over which the monthly payment is calculated as if the loan were fully amortizing (e.g. 30). Range: > 0, ≤ 100
`balloon_after_years`	number	years	yes	Years until the remaining balance is due as a lump sum; must be shorter than amortization_years. Range: > 0, ≤ 100

Outputs

Output	Type	Unit	Description
`monthly_payment`	number		Level payment that would amortize the loan over amortization_years.
`payments_before_balloon`	integer		Number of monthly payments made before the balloon, 12 × balloon_after_years.
`balloon_payment`	number		Remaining balance due with the last scheduled payment (closed-form remaining balance).
`principal_paid_before_balloon`	number		loan_amount − balloon_payment.
`total_paid_before_balloon`	number		monthly_payment × payments_before_balloon (excluding the balloon).
`total_interest`	number		total_paid_before_balloon + balloon_payment − loan_amount.
`total_cost`	number		total_paid_before_balloon + balloon_payment: everything paid over the life of the loan.
`balloon_share_of_loan_percent`	number	%	balloon_payment / loan_amount × 100.

Example

200,000 at 6 %, 30-year amortization, balloon after 7 years: {"loan_amount":200000,"interest_rate_percent":6,"amortization_years":30,"balloon_after_years":7} → {"monthly_payment":1199.1,"payments_before_balloon":84,"balloon_payment":179278.77,"principal_paid_before_balloon":20721.23,"total_paid_before_balloon":100724.49,"total_interest":80003.26,"total_cost":280003.26}

500,000 at 7 %, 25-year amortization, balloon after 5 years: {"loan_amount":500000,"interest_rate_percent":7,"amortization_years":25,"balloon_after_years":5} → {"monthly_payment":3533.9,"payments_before_balloon":60,"balloon_payment":455810.76,"total_paid_before_balloon":212033.76,"total_interest":167844.52,"total_cost":667844.52}

GET https://tttkmbb.com/api/v1/calculate/balloon-loan?loan_amount=200000&interest_rate_percent=6&amortization_years=30&balloon_after_years=7

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/balloon-loan (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/balloon-loan · Markdown: https://tttkmbb.com/finance/balloon-loan.md · JSON definition: https://tttkmbb.com/finance/balloon-loan.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="balloon-loan"
OpenAPI operationId: calculate_balloon_loan
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

CFPB – What is a balloon payment? When is one allowed? (government)
Wikipedia – Balloon payment mortgage (reference)
Wikipedia – Amortization calculator (annuity payment formula) (reference)

FAQ

Why is the balloon still so large after 7 years?

Early payments of a 30-year amortization are mostly interest: on 200,000 at 6 % only 20,721 of the 100,724 paid in the first 84 months is principal, leaving 179,279 due.

Is the balloon included in total_interest?

No. The balloon is repayment of principal; total_interest = all monthly payments + balloon − loan_amount, which is the interest actually charged over the 7 years.

What happens at the balloon date?

The borrower must pay the balance in cash, refinance it or sell the asset; if refinancing is unavailable the loan defaults, which is why CFPB rules restrict balloon features in qualified mortgages.

Related calculators

Amortization Schedule Calculator — Full year-by-year balance of the amortization.
Loan Payment Calculator — Fully amortizing payment over any term.
Interest-Only Loan Calculator — Alternative structure with interest-only payments before amortization.