Picture two home loans with the same headline rate. Over the life of the loan, the total cost can differ by about $11,000. That gap is why this post exists. If you are new to home loans, mortgage calculators can help you compare options, but only when you ask the right question. We will walk through the handful that matter: repayment, loan comparison, borrowing power and extra repayment calculators. You will see what each one tells you. You will also see what it misses and how a comparison rate changes the picture. Then we compare two loans on the same headline rate by total cost, not the rate on the screen. We will also look at where to find calculators without wading through sales pages. We will cover what no calculator can tell you. Then we will show how to bring a better question to the numbers.
Two loans, same headline rate, about $11,000 apart
Picture two loan offers on the kitchen table. Both advertise the same headline rate, so they look like the same deal with a different logo. They are not.
Take a $600,000 loan over 30 years at an illustrative rate of 6.00% p.a., with monthly repayments near $3,598. One offer carries a $395 annual fee. The other has no annual fee but a $600 establishment fee. Same rate and same repayment. Over the full term, the difference in fees alone can run to roughly $11,000. Over three years, that gap shrinks to a few hundred dollars.
Every figure here is hypothetical. It exists to show the maths, not to quote any rate you could get today.
That gap is the point. A headline rate is what a lender advertises. Total cost is what you pay, and that includes fees, how long you keep the loan and how the interest is calculated. This guide walks through the four calculators worth your time, what each can and cannot tell you, then runs both loans side by side on total cost.
A calculator is only as good as the question you bring to it
Now that you have two loans side by side, which calculator should you use? It is the question we hear most, and the honest answer is that the tool matters far less than the question you bring to it. A calculator takes your inputs, applies a formula, and hands back a confident-looking number. Feed it vague inputs such as “about 30 years” or “a rate I saw online” and the answer may not mean much. The calculators on our website work the same way, so start with a clear question. Think of it like a kitchen scale: it tells you the weight of what you put on it, but it has no view on whether the recipe will work. Treat the numbers as a starting point rather than a verdict. The sections below answer each of those four questions in turn.
The repayment calculator: what your fortnight actually looks like
First question: what will your repayments actually be?
Hypothetically, borrow $600,000 over 30 years at the illustrative rate assumed throughout this article and you get roughly $3,598 a month, or about $1,660 a fortnight. That is what a repayment calculator does. It takes three inputs, the amount, the term and the rate, then turns them into one regular figure you can view monthly, fortnightly or weekly.
What it cannot do is assess you. It knows nothing about your income, your living costs or whether a lender would look at a $600,000 application and approve it.
The trap is the term. Stretch the same loan from 25 years to 30 and the fortnightly figure drops, yet the total interest climbs. You can pay fortnightly instead of monthly to push the other way.
For a neutral starting point, try Moneysmart’s mortgage calculator.
The loan comparison calculator: the one that adds up total cost
The repayment calculator tells you what one loan costs each month. It can’t tell you which of two loans costs less overall. That’s the job of a loan comparison calculator, which lines up two or more loans and totals repayments plus ongoing fees across a set period.
Expect to enter a loan amount, term, each loan’s rate, ongoing fees and any upfront or exit costs. Check the exact fields on whichever tool you use, because they vary.
The comparison period changes the answer. Over three years upfront fees dominate. Over 30 years ongoing fees quietly overtake them.
The common trap is lining up loans with different terms or different fee structures as though they were identical.
For a neutral read on total cost, Moneysmart’s mortgage switching calculator is the most relevant government-backed tool. It has no product to sell, which is exactly why it is a good place to start.
What a comparison rate really includes
The loan comparison calculator adds up total cost over a set period. A comparison rate squeezes a loan’s rate and most of its fees into one percentage, so different loans are easier to line up side by side.
Some costs sit outside it. Government charges are one example. Fees that only apply in specific circumstances are another. Check what is and is not included for any loan you are comparing.
The standard warning that accompanies a comparison rate notes it is a guide to comparing costs, not a complete picture of what you will pay.
There’s a practical limit. It’s calculated on a set loan amount and term, so it may not reflect what you actually borrow or how long you really keep the loan.
So when you see an advertised rate, ask for the comparison rate beside it before you take the number seriously.
The borrowing power calculator: how much a lender might lend
Comparison rates tell you what a loan costs. They don’t tell you whether a lender will lend you the money. For that, you want the borrowing power calculator.
It takes your income, your debts, your living expenses and how many dependants you have, then returns a borrowing range. Lenders each run their own affordability assessment, so two lenders can return different figures for the same household. Getting income versus expenses right matters here, because the expense figure you enter shapes the result more than most people expect.
Here’s the awkward bit. The number on screen is an estimate, not an approval. No calculator can approve a loan.
Estimates drift where income is uneven. Variable or irregular income — such as overtime, casual earnings or rent — tends to be assessed more conservatively, and the treatment varies.
Use it as a planning range before you start inspecting properties, not as a spending target for your weekend auction. Once you have that range, the next question is what happens if you pay a little extra.
The extra repayment calculator: what a small change does over time
Borrowing power tells you your range. This tool tells you what happens if you pay more than the minimum. It shows how extra repayments, or a more frequent schedule, change the total interest you pay and the time you spend in debt.
Say you add $200 a month to the illustrative $3,598 repayment. The loan finishes sooner. The interest bill drops. The earlier you start, the bigger the difference, because most interest is charged in the early years.
There’s an assumption baked in: that you keep making those extra payments every month without a pause. Miss a few months and the maths shifts.
The catch sits in the conditions. Some loans restrict extra repayments, particularly during a fixed period, so read the fine print and any recent lending policy changes before you plan around it.
An offset account is a related but different lever. Money parked there reduces the balance interest is calculated on. The figures above are hypothetical, used only to show the maths.
The harder question is comparing two loans. That’s next.
Worked example: two loans on the same headline rate, compared on total cost
Here is where the offset conversation gets real. Using the same hypothetical setup from the opening section — $600,000 over 30 years at the same illustrative rate — here is what the total cost comparison actually looks like.
Loan one carries an annual fee and an offset account. Repayments total roughly $1,295,000, plus annual fees accumulated over 30 years. Loan two charges no annual fee, but has an establishment fee and a discharge fee. The same repayments plus establishment costs produce a different total.
Now the twist. Keeping $20,000 in an offset account cuts interest on that amount. That saving compounds if the balance stays put.
So the loan with the annual fee is not automatically worse. The answer shifts with how long you hold the loan and how much you keep offset. Compare total cost across your own timeframe. If a loan splits fixed and variable portions, split rate loans add another layer to check.
All figures are hypothetical. Any rate should sit beside its comparison rate, remembering that the standard warning notes a comparison rate is a guide to comparing costs, not a complete picture of what you will pay.
Where to find calculators without wading through sales pages
Now you have the maths, where do you actually run it?
Start with Moneysmart. Its mortgage calculator and mortgage switching calculator are government-backed and neutral, with no product to sell you. For a second opinion, run the same numbers through another tool and check whether the answers broadly agree. If they don’t, work out why before trusting either one.
Lender and comparison site calculators often end with a prompt to enquire. That is no reason to distrust the arithmetic. Just keep your original question in front of you.
At Time Home Loans we compare loans across a panel of lenders, and in most cases there’s no broker fee to pay. Booking a complimentary chat is straightforward.
What no calculator can tell you
Here is the awkward bit. No calculator knows your job security, whether children are on the horizon, the renovation list you keep adding to, or how you would feel about a lender if something went wrong at settlement.
They also cannot see lender policy. Variable income sources and existing study debts can affect the result, and different lenders weigh them differently. Same household, different answer.
Fine print is invisible too. Conditions around extra repayments and redraw sit in the loan terms, not in any formula.
Our honest view: these tools narrow the field. They do not choose your loan. A conversation about your circumstances is what turns a shortlist into a decision.
Bring a better question to the calculator, then have a chat
Each of those four tools answers one question well and the rest badly. So write your question down first. What will I repay? Which loan costs less overall? How much might I borrow? What changes if I pay extra? Then run your numbers through a neutral tool such as Moneysmart. Where you see an advertised rate, check the comparison rate sitting beside it.
Second, compare loans on total cost across the timeframe you genuinely expect to hold the loan. The headline rate alone will not settle it.
When you are ready to talk it through, book a complimentary chat with Time Home Loans. In most cases there’s no broker fee to pay.
This article is general information only and does not take into account your objectives, financial situation or needs. Seek advice before acting. Lending criteria, fees and charges apply. Time Home Loans Pty Ltd ABN 53 161 695 012 is Credit Representative 529395 of outsource Financial Pty Ltd, Australian Credit Licence 384324.
