How to Calculate Your Mortgage Repayments Online

One of the biggest mistakes first home buyers make is walking into a bank meeting without any idea what their repayments will be. Lenders will give you a number, but without your own independent calculation, you have no way to check it or compare it against other offers.

This guide shows you how to calculate your mortgage repayments using LoanLens — a browser-based calculator that runs entirely on your device, supports multiple countries, and gives you a complete amortisation schedule you can export to Excel.

What a mortgage calculator actually tells you

Before jumping into the steps, it's worth understanding what you're calculating. A mortgage calculator takes three core inputs and produces several important outputs:

The three inputs:

• Loan amount — the amount you're borrowing (purchase price minus your deposit)
• Interest rate — the annual interest rate your lender charges, expressed as a percentage
• Loan term — the number of years over which you'll repay the loan (typically 25–30 years)

The key outputs:

• Monthly repayment — the fixed amount you'll pay each month
• Total repayment — the full amount you'll pay over the entire loan term
• Total interest — how much extra you'll pay above the amount borrowed
• Amortisation schedule — a month-by-month breakdown showing how each payment splits between principal and interest

The amortisation schedule is particularly revealing. In the early years of a mortgage, most of your monthly payment goes toward interest, not the loan itself. Understanding this helps you see why making extra repayments early can save tens of thousands of dollars over the life of a loan.

Step-by-step: Using LoanLens to calculate your repayments

An example: $600,000 mortgage at 6.5% over 30 years

To make this concrete, here's what a typical Australian mortgage looks like with current approximate rates:

That total interest figure — more than the original loan amount — is why understanding your mortgage early is so important. Even small differences in interest rate, loan term, or extra repayments can translate to significant savings over 30 years.

How to compare different loan scenarios

One of the most useful things to do with a mortgage calculator is run multiple scenarios side by side. Try these comparisons:

• 25 years vs 30 years: A shorter term means higher monthly payments but significantly less total interest. Calculate both and see the difference.
• 6.5% vs 6.0% rate: Even a 0.5% difference in interest rate changes your repayment by hundreds of dollars a month on a large loan.
• Extra repayments: If you can afford an extra $200/month above your minimum repayment, how many years does it shave off your loan? LoanLens's savings planner helps answer this.

What LoanLens doesn't include

LoanLens is a pure calculator — it doesn't account for some real-world costs you'll face as part of home ownership. Make sure you separately budget for stamp duty (or land transfer tax), lender's mortgage insurance (LMI) if your deposit is under 20%, conveyancing fees, building and pest inspections, and ongoing council rates and strata fees if applicable. These costs vary significantly by location and lender, so it's important to get accurate figures from your specific providers.