Interest-Only Mortgage Calculator
Interest-Only Mortgage Calculator Work Out the Real Cost
This interest-only mortgage calculator estimates your repayment during an interest-only period and what it jumps to once the loan reverts to principal and interest. Enter your loan amount, interest rate, loan term, repayment frequency, interest-only period, and any loan fee, and it returns both repayment figures, along with total interest and fees payable and total payments across the loan.
The gap between the two repayment figures is often larger than borrowers expect, since none of the balance is being reduced during the interest-only period. Output is an estimate based on your inputs, not a loan offer.
Why the Repayment Jump After Interest-Only Catches People Off Guard
During an interest-only period, your repayment covers only the interest charged, so the loan balance doesn’t move. Once that period ends, the remaining balance needs to be repaid over whatever’s left of the original term, which is now a shorter window than a standard principal and interest loan would have used from day one.
On a $400,000 loan with a 5-year interest-only period inside a 30-year term, the interest-only repayment might sit around $2,000 a month, then jump to over $2,500 a month once principal repayments start on the remaining 25 years. This interest-only home loan calculator shows both figures upfront so the jump isn’t a surprise partway through the loan. The loan balance chart also shows this visually, the balance stays close to flat during the interest-only years before dropping more steeply once principal repayments begin.
How to Use the Calculator
You’ll need the loan details you’re considering or currently have:
Loan amount and interest rate
Loan term, total years
Repayment frequency, weekly, fortnightly, or monthly
Interest-only period, in years
Loan fee, if applicable
The interest-only repayment calculator returns your repayment during the interest-only period, your repayment once it reverts to principal and interest, total interest and fees payable, and total payments over the full term. Run it with different interest-only period lengths to see how a shorter or longer interest-only window changes the size of the repayment jump.
How ADA Financial Services Helps
An interest-only period calculator shows you the numbers on a standard structure. A broker looks at whether interest-only actually suits your situation, whether that’s cash flow management on an investment loan or a specific short-term need, and what the loan looks like once that period ends.
ADA Financial Services compares interest-only and principal and interest structures across our lender panel, and models what your repayment looks like both during and after the interest-only period before you commit. Our fee is paid by the lender at settlement in most standard cases, disclosed in writing before any application proceeds. We’re based on the Sunshine Coast and work with borrowers across Northern Australia.
Considering an interest-only loan and want to see the full picture?
Speak with an ADA Financial Services specialist about your options. We model both repayment figures on your actual numbers and give you a clear, honest answer on whether interest-only fits your situation.
This is general information only and does not constitute financial or credit advice. Speak to a licensed broker for advice tailored to your situation.
FAQs
Why is my repayment so much higher after the interest-only period ends?
Because none of the loan balance was reduced during the interest-only period, the full remaining balance needs to be repaid over a shorter timeframe once principal and interest repayments start, which increases the monthly amount.
Is an interest-only loan more expensive overall than principal and interest?
Generally yes, since more of the loan balance is outstanding for longer, meaning more total interest is charged across the life of the loan compared to a standard principal and interest structure from day one.
Who typically uses an interest-only structure?
It’s most common on investment properties for cash flow management, or short-term situations such as a planned sale or income change. It’s less commonly suited to a standard owner-occupier home loan held long-term.
Can I extend my interest-only period once it ends?
Some lenders allow this, subject to a new application and approval, but it’s not automatic. It’s worth confirming your lender’s policy before relying on an extension.
What This Loan Repayment Calculator Shows
This loan repayment calculator estimates what you will pay each month on a home loan, how much of that payment goes to interest versus principal, and the total interest charged across the full term. You enter your loan amount, interest rate, term, and repayment frequency. The output gives you a clean repayment figure to plan around and a total cost number that most borrowers underestimate.
The estimate is based on the inputs you provide and assumes a standard principal and interest loan with a constant interest rate. Real loans vary as rates move and fees apply. Treat the output as a planning figure, not a loan offer.
What This Loan Repayment Calculator Shows
This loan repayment calculator estimates what you will pay each month on a home loan, how much of that payment goes to interest versus principal, and the total interest charged across the full term. You enter your loan amount, interest rate, term, and repayment frequency. The output gives you a clean repayment figure to plan around and a total cost number that most borrowers underestimate.
The estimate is based on the inputs you provide and assumes a standard principal and interest loan with a constant interest rate. Real loans vary as rates move and fees apply. Treat the output as a planning figure, not a loan offer.