Interest-only payments now, the amortization jump later — both numbers, honestly
$—
IO Payment (Years 1–10)
$—
Payment After (Years 11–30)
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Payment Jump
Interest-only loan
Standard 30-yr loan
Remaining balance Interest paid to date Total paid to date
The balance holds flat through the interest-only years (nothing is paid down), then follows a standard amortization schedule once the IO period ends.
An interest-only loan charges you rent on your own debt: for the IO period (usually 5–10 years) you pay interest and nothing else, the balance never falls, and then the entire principal must amortize in the years that remain — at a sharply higher payment. It's a legitimate cash-flow instrument for specific borrowers and a trap for everyone else. This calculator shows both payments, the jump between them, and what the structure costs versus a standard loan over the same life.
The Structure in One Example
$400,000 at 7.0%, 10-year IO, 30-year term: the IO payment is $2,333 — pleasantly below the standard loan's $2,661. But at year 11 the untouched $400,000 must amortize in 20 years: the payment becomes $3,101, a 33% jump, and the lifetime interest runs about $64,000 higher than the standard loan. The discount decade is repaid, with interest, by the compressed two that follow.
Who Actually Uses IO Loans Well
Irregular high earners (commission, carry, bonuses): pay IO as the floor, then throw lump sums at principal on good years — most IO loans permit unlimited prepayment, making the structure a flexible minimum rather than a plan to pay nothing.
Real-estate investors maximizing cash flow and deductible interest on properties they intend to sell or refinance within the IO window (cap-rate math in the Cap Rate Calculator).
Short-horizon owners confident of selling before amortization begins — accepting that if the market stalls, they own the cliff.
The Risks, Named
Risk
Mechanism
Payment shock
+25–45% at the IO cliff, by design — the calculator's jump figure
Zero payment-built equity
Ten years of payments, same debt; a flat market leaves you exactly where you started, minus the interest
Refinance dependence
The common 'plan' for the cliff assumes rates, income and home value all cooperate a decade out
Rate premium
IO pricing runs ~0.25–0.5% above standard — you pay extra for the privilege of deferring
IO vs Just Taking the Standard Loan
The comparison table in the results states it plainly: same rate, same term, the IO structure costs more in total interest — the only thing it buys is lower payments early. If early cash flow is the genuine constraint, compare alternatives first: a longer standard term, buying less house (Affordability Calculator), or an ARM whose discount you at least get paid for taking.
How to Use the Calculator
Enter loan, rate (your actual IO quote — it's usually above the standard quote), IO period and total term.
Read both payments and the jump percentage — then imagine the jump landing in a bad year.
Check the comparison table's last row: the lifetime price of the early relief.
Frequently Asked Questions
Can I pay principal during the IO period?
Almost always yes, without penalty — and it's the redeeming feature: the IO payment is a floor, not a ceiling. Voluntary principal reduces both future interest and the size of the eventual amortizing payment.
Do IO mortgages still exist after 2008?
Yes, but outside the qualified-mortgage mainstream: they're portfolio and jumbo products for stronger borrowers (high credit, low LTV, documented assets), not the no-doc teasers of 2006.
Is the IO payment tax-deductible?
Mortgage interest rules apply the same as any home loan — deductible up to the acquisition-debt cap if you itemize. Since the whole payment is interest, IO borrowers who itemize deduct the whole payment; investors deduct it as an expense regardless.
What happens if I can't afford the post-IO payment?
The standard exits are refinancing (rate risk), selling (market risk) or recasting after big principal payments. Having none of the three is how IO loans end badly — decide your exit before signing, not at year nine.
IO loan or ARM — which 'discount' structure is better?
They solve different problems: an ARM discounts the rate with reset risk; IO defers principal with cliff risk. ARMs at least amortize. If you must pick an exotic, the modern capped ARM is usually the safer of the two.
Why is my quoted IO rate higher than the standard rate?
Deferred principal is extra risk to the lender — slower equity build means higher loss severity if you default. The 0.25–0.5% premium is that risk, priced.
Is my information private?
Yes — every calculation is local to your browser.
An interest-only loan is a cash-flow tool wearing a mortgage costume — powerful in the hands of someone with a real exit and lumpy income, corrosive as a way to afford more house. If the standard payment doesn't fit, the honest fix is the price of the house, not the shape of the loan.