This calculator provides an estimate only. Actual repayments can change with variable rates, lender fees, and loan contract terms.
If you are searching for a mortgage repayments calculator interest only, you are probably trying to answer one important question: “What will this loan really cost me each month?” This page gives you both a practical calculator and a clear explanation of how interest-only home loans work, so you can compare options with confidence.
What is an interest-only mortgage?
An interest-only mortgage is a loan where your regular repayments cover interest charges, but do not reduce the principal balance during the interest-only period. That means your loan amount stays the same until that period ends.
For example, if you borrow $500,000 and only pay interest for 5 years, you will still owe $500,000 at the end of those 5 years (unless you make extra principal payments).
How this calculator works
For an interest-only loan, the basic repayment estimate is:
- Monthly repayment = (Loan Amount × Annual Interest Rate) ÷ 12
- Fortnightly repayment = (Loan Amount × Annual Interest Rate) ÷ 26
- Weekly repayment = (Loan Amount × Annual Interest Rate) ÷ 52
The calculator above also includes an optional monthly fee so you can build a more realistic estimate.
Example: quick interest-only repayment estimate
Suppose you have:
- Loan amount: $500,000
- Interest rate: 6.5% p.a.
- Interest-only period: 5 years
Your annual interest cost is around $32,500. That is approximately $2,708.33 per month before fees. Over 5 years, you would pay about $162,500 in interest, and still owe the original $500,000 principal.
Interest-only vs principal and interest
Interest-only loan
- Lower repayments at the start
- Cash-flow friendly in the short term
- Principal does not reduce automatically
- Can cost more in total interest over time
Principal and interest loan
- Higher regular repayments
- Builds equity sooner
- Balance declines over time
- Often lower total interest over full loan life
When an interest-only mortgage might make sense
An interest-only structure can be useful in specific situations, such as:
- Temporary cash-flow pressure
- Property investors focused on short-term holding
- Borrowers expecting a near-term income increase
- People planning to sell before principal repayments begin
It is generally most effective when used with a clear strategy and timeline.
Risks to understand before choosing interest-only
1) Repayment shock later
When the interest-only period ends, repayments can rise significantly if the loan converts to principal and interest over the remaining term.
2) Rate rises
If your mortgage rate is variable, even your interest-only repayment can increase quickly.
3) Slower equity growth
Because principal is not reduced, your equity may grow only through property value increases, which are never guaranteed.
4) Higher total cost
Paying interest without reducing the balance often means paying more total interest compared with a principal-and-interest strategy.
How to use this calculator effectively
- Run multiple scenarios at different interest rates (e.g., 6%, 7%, 8%).
- Add realistic monthly fees so your estimate is closer to real lender costs.
- Compare monthly, fortnightly, and weekly views to match your pay cycle.
- Estimate the full interest-only period cost, not just one repayment.
- Plan for what happens when the interest-only period ends.
Smart planning tips
If you decide to go interest-only, consider these risk controls:
- Keep a cash buffer for rate increases.
- Make occasional extra principal payments if allowed.
- Review your refinance options before the interest-only period ends.
- Track your loan-to-value ratio and long-term equity goals.
- Get tailored advice from a licensed mortgage professional.
Final thoughts
A good mortgage repayments calculator for interest-only loans should do more than show one payment number. It should help you understand the trade-off between short-term affordability and long-term cost.
Use the calculator above as a decision tool: test scenarios, compare outcomes, and plan ahead so your mortgage supports your broader financial goals.