How this instrument works
A partially amortized loan sizes its monthly payment against one repayment schedule — often 25 or 30 years — while the note itself legally matures on a separate, earlier date. In a standard residential mortgage those two numbers are the same, so the distinction rarely comes up; a 30-year mortgage amortizes over 30 years and is due in 30 years. Commercial mortgages, SBA second-lien notes, and seller-financed real estate deals routinely decouple them, and reading 'amortized over 30 years' as 'due in 30 years' is the single most common misreading of a note built this way.
The payment side of the arithmetic only needs the amortization schedule — loan amount, rate, and the number of months the payment is stretched over. The balloon side takes that same fixed payment and projects the loan's compounding forward through the loan's actual length instead, then reads off whatever principal is still outstanding at that stopping point. It is the identical formula an amortization table uses; this instrument just evaluates it at month k instead of walking all N months and printing every row.
Because the schedule length and the actual term are set independently, this calculator is most useful for testing structure rather than reading a single answer: a broker comparing a lender's 7-year, 10-year, and 15-year maturities against the same 30-year schedule, or a note investor pricing what principal remains on a seller-financed note before deciding what to pay for it. None of that pricing is arithmetic the formula performs — it returns the contractual balance only, not what an early-maturing note is worth to a buyer, what a lender will charge to refinance it, or whether refinancing will be available at all before it matures.
- Enter the amount financed under Loan amount, $.
- Set the note's rate under Annual interest rate, %.
- Enter the longer schedule the payment is computed against under Amortization schedule, years — often 25 or 30.
- Enter the shorter, actual maturity under Actual loan term, years — this is when the loan is really due.
- Read Monthly payment, $ and Balloon payment due at term end, $ — the lump sum still owed once the loan reaches that date.
Worked example — a $300,000 note on a 30-year schedule
Take a $300,000 loan at 6% annual interest, with the payment computed against a 30-year amortization schedule. The payment formula returns $1,798.65 a month regardless of how long the note is actually outstanding — it only knows the schedule, not the real maturity. Set the actual loan term to 7 years and the balloon formula projects that fixed payment through 84 months, leaving $268,918.16 of the original $300,000 still owed the day the note matures.
Nothing else about the note changes if the actual term is negotiated longer instead. Stretch it to 15 years on the identical $300,000 schedule and the same $1,798.65 payment now runs for 180 months before the balloon comes due, cutting the outstanding balance to $213,146.53. Push the actual term out to the full 30 years — matching the amortization schedule exactly — and the balloon collapses to zero, because a partially amortized loan run to the end of its own schedule is simply a fully amortized one.
Questions
What does 'partially amortized' mean?
It means the monthly payment is computed against one repayment schedule — the amortization period — while the note's legal maturity falls on a separate, shorter term. A loan run to the end of its own amortization schedule is fully amortized; a loan with no principal reduction at all is interest-only. This structure sits between the two: real principal repayment, just not enough of it before the note comes due.
How is this different from a balloon loan?
It is not a different loan — 'partially amortized' describes the structure, and 'balloon payment' describes the lump sum that structure produces at maturity. This calculator is built to compare structures: hold the loan amount, rate, and schedule fixed, then change only the actual term to see how much the eventual balloon shrinks or grows.
Why would a lender set the term shorter than the amortization schedule?
Commercial lenders often limit how long they hold a fixed-rate loan on their books to manage interest-rate exposure, even when the borrower wants a payment sized as if the loan ran 25 or 30 years. Sizing the payment on the long schedule keeps it affordable; capping the actual term at 5, 7, or 10 years limits the lender's commitment and pushes refinancing risk onto the borrower.
Does a longer actual term always shrink the balloon?
Yes, holding the loan amount, rate, and amortization schedule fixed. Every additional month of payments retires a little more principal, so the balance still owed at maturity falls the further out the actual term is set — until it equals the amortization schedule, at which point the balloon reaches zero and the loan is simply fully amortized.
Does this figure what a note is worth if I buy or sell it early?
No. The balloon figure is the contractual principal balance the arithmetic implies — it says nothing about the price a note investor should pay for that balance today, what discount a buyer might demand, or what rate a lender will offer to refinance it once the loan matures. Those depend on market conditions this formula does not model.
What happens if the actual term is set longer than the amortization schedule?
The structure stops making sense — a loan cannot still be outstanding after its own amortization schedule has already paid it to zero. This sheet flags actual terms longer than the amortization schedule as invalid rather than returning a negative balance.
References
Read this first: This instrument shows arithmetic, not advice. Real offers add fees, taxes and terms that vary by lender and place — verify the figures against your actual paperwork before deciding anything.