Interest-Only Calculator
Compare an interest-only payment to a fully-amortizing one and see the jump when the interest-only period ends.
By Onias Derilus, Mortgage Capital · NMLS# 1859012 · Last Updated: June 2026
Interest-Only vs Amortizing
During the interest-only period the balance does not fall. When it ends, the loan re-amortizes over the remaining term, raising the payment. Estimate only.
An interest-only loan lets you pay just the interest for an initial period, which keeps the early payment low. The principal does not shrink during that time, so you build no equity from payments.
When the interest-only period ends, the loan re-amortizes over the remaining years and the payment jumps. These loans suit borrowers with variable income or a clear plan to sell, refinance, or pay lump sums.
These figures are estimates. For neutral, official guidance on mortgage costs and what lenders can charge, see the CFPB's Owning a Home guide.
How to Use This Calculator
- 1
Enter your loan amount.
- 2
Set an illustrative interest rate.
- 3
Choose the length of the interest-only period.
- 4
Compare the interest-only payment to the fully-amortizing payment and the higher payment that follows.
The Formula & Assumptions
Interest-only = loan × rate ÷ 12
After IO period, re-amortize
the balance over the remaining
years at the same rate.
During the interest-only period you pay only the monthly interest on the full balance, so the payment is lower but the principal stays unchanged.
When the period ends, the same balance must be repaid over the years that remain, which produces a higher payment than a loan that amortized from day one.
Interest-only loans are usually non-QM or jumbo products with stricter credit and reserve requirements. They work best when you have a defined exit — a sale, refinance, or expected liquidity event.
Frequently Asked Questions
How does an interest-only mortgage work?
For an initial period you pay only the interest, keeping the payment low, but the balance does not decrease. After that period the loan re-amortizes over the remaining term and the payment rises.
Who should consider an interest-only loan?
Borrowers with irregular or bonus-heavy income, investors managing cash flow, or buyers who plan to sell or refinance before the period ends. It requires discipline since you build no equity from payments during the IO phase.
Do I build equity during the interest-only period?
Not from your payments: the principal stays flat. You only gain equity through home appreciation or by making voluntary principal payments, which most interest-only loans allow.
What happens when the interest-only period ends?
The loan converts to fully amortizing. The remaining balance is spread over the years left in the term, so the payment increases — sometimes significantly. Plan for that jump before choosing this structure.
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Rates are illustrative only. APR and payments vary by credit score, loan amount, and market conditions. Subject to credit approval. Not a commitment to lend. NMLS# 1859012. Equal Housing Lender.
It estimates payments on an interest-only mortgage during the interest-only period. It also shows the higher fully-amortizing payment that begins once principal repayment kicks in.
Interest-Only Calculator in Florida
Interest-only loans appear most often in Florida's luxury and investment markets, where buyers may prefer lower carrying costs or expect to sell within a few years. Because the strategy depends on appreciation or a future payoff, weigh it against the state's insurance costs, which you owe regardless of how the loan is structured.
How the Interest-Only Calculator Works
During the interest-only period the calculator charges only the monthly interest, with no principal reduction. After that period it amortizes the full balance over the remaining term, producing a noticeably higher payment.
The Interest-Only Formula, Explained
IO payment = balance × rate / 12; later payment amortizes over remaining term
Interest-only payments are lower because they do not reduce the balance. The catch is that when the interest-only period ends, the same balance must be repaid over fewer remaining years, which raises the payment sharply.
These loans suit borrowers with irregular income or a clear plan to sell, refinance, or pay a lump sum before the payment jumps. The calculator shows both payment levels so the step-up is visible.
The Complete Interest-Only Calculator Guide
An interest-only mortgage lets you pay just the interest for an initial period, keeping payments low. It is a cash-flow tool, useful for borrowers with uneven income or those who expect a lump sum, but it builds no equity during the interest-only years.
The defining feature is the payment jump. When the interest-only window closes, the full balance amortizes over the years that remain, so the payment can rise substantially. Planning for that step-up is the whole game.
These loans reward a clear exit: a sale, a refinance, or a planned principal paydown before the jump. Without one, the rising payment can become a strain. Use the calculator to see exactly how much the payment increases and when.
Interest-Only Calculator FAQ
Do I build equity with an interest-only loan?
Not during the interest-only period, since you pay no principal. Equity grows only through appreciation until principal payments begin or you pay down the balance.
How much does the payment rise later?
Significantly, because the full balance must amortize over the remaining, shorter term. The calculator shows the exact step-up so you can plan for it.