How is interest calculated on a home loan?

Your home loan interest rate determines how expensive your mortgage repayments are. Learn how interest is calculated on your loan, and how you can pay it off sooner.

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There are two parts to a mortgage repayment: the principal and the interest. You pay back both the money you borrow (the principal) and the interest (charged by the lender). This interest adds up to a huge chunk of money on top of your original loan amount – but the good news is, there are ways to save on interest and own you own home sooner.

From the Reserve Bank’s cash rate to the amount you borrow, there are several factors that affect the amount of your interest repayments. Let’s take a closer look at how home loan interest is calculated.

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What factors affect the amount of interest you pay?

The following factors will affect the amount of your interest repayments:

  • The home loan interest rate. This is the rate at which the bank charges you interest on the loan, such as 3% p.a. Some loans offer a reduced interest rate for an introductory period, which then reverts to the standard rate.
  • The Reserve Bank Official Cash Rate. The interest rate on your loan is based on the official cash rate set by the Reserve Bank of Australia on the first Tuesday of each month (except January). The official cost of borrowing can prompt lenders to charge a higher or lower amount of interest. The current cash rate can be found here.
  • The amount you borrow. The larger the sum you borrow from your bank, the more interest you will pay – but also, some banks offer discounted interest rates for larger loan amounts.
  • The outstanding loan amount. As you gradually pay off the money you borrow, you will be paying interest on a smaller loan amount and your interest payments will therefore slowly reduce. For example, your interest repayments when you first start paying off a $500,000 loan will be much larger than when you’ve paid off half of the principal amount, and interest is only payable on $250,000.
  • The number of days in the month. Most lenders calculate interest on home loans daily and then charge that interest to you each month. With this in mind, you could pay a smaller amount of interest in February (with 28 days in the month) than you do in March (with 31 days).
  • The loan term. The time you take to pay off your loan will affect the amount of interest you pay – paying your loan off over a shorter period of time will minimise your interest repayments.
  • Repayment frequency. Most lenders allow you to make repayments weekly, fortnightly or monthly, so the amount of interest you pay each time will vary depending on your repayment schedule. The more frequently you make repayments, the less interest you will pay on your loan. Use our bi-monthly calculator to see how your interest payments will vary depending on your repayment frequency.
  • Whether you have an offset account. Some home loans come with a linked offset account, which allows you to reduce the amount of interest you pay on your loan. For example, if you borrow $300,000 from the bank but you have $50,000 on a linked 100% offset account, you will only pay interest on $250,000.

How is home loan interest calculated?

Interest on your home loan is generally calculated daily and then charged to you at the end of each month. Your bank will take the outstanding loan amount at the end of each business day and multiply it by the interest rate that applies to your loan, then divide that amount by 365 days (or 366 in a leap year).

Home loan interest calculationAssuming you have an outstanding loan amount of $500,000 and an interest rate of 3% p.a., your interest repayment for one day would be calculated using the following formula:

($500,000 x 0.03) ÷ 365 = $41.10

At the end of the month, each daily interest charge is added together and then charged to your loan. To work out how much your interest repayments will be, input the details of your loan into our home loan interest calculator below.

Principal and interest vs interest-only

There’s another factor that can affect your regular home loan repayment amount: whether you are making principal and interest or interest-only repayments. Principal and interest repayments are the most common way to pay off a home loan, and they basically mean that one portion of your repayment goes towards paying off the amount you borrow and another portion goes to paying off the interest you owe.

However, some loans are designed to allow you to make interest-only repayments for a certain period, for example if you’re building a new home or if you’re a property investor with an investment mortgage. This allows you to reduce your regular repayment amount.

Susie’s Mortgage Repayments

How is home loan interest calculator case studyIn our hypothetical case study, Susie is borrowing $700,000 to buy a house. Like most borrowers, she wants to save as much money on interest repayments as she possibly can. After comparing home loans with 100% offset accounts, Susie decides to calculate just how much difference a 0.25% p.a. difference in interest rates could make to the total cost of a loan.

If she can find a loan with an interest rate of 3% p.a. on a 30-year loan term, her monthly principal and interest repayments will be $2,951. The total interest she will end up paying over the life of the loan is $362,442.

But if Susie finds a loan with a marginally lower interest rate of 2.75% p.a., her monthly repayments will be $2,858 – a saving of $93. The total interest over the life of the loan will be $467,051.29 — that’s a total interest saving of $33,480.

How to save interest on your home loan

Now that you know a bit more about how interest is calculated let's look at the ways you can actually pay less of it.

  • Get the best rate. Shopping around for a better interest rate can save you thousands of dollars, you may want to even consider refinancing with your current lender or switching to a new lender.
  • Look for an offset account. Home loans with offset accounts allow you to reduce the principal amount that you need to pay interest on, by literally "offsetting" the loan principal with your savings. It's a powerful and free way to super-charge your mortgage repayments.
  • Make frequent repayments. The more frequently you make regular loan repayments, the less interest you will have to pay, as interest is calculated daily – so even paying weekly or fortnightly instead of a monthly can help you make headway.
  • Make extra repayments. The ability to make extra repayments without penalty can work strongly in your favour, as extra repayments off the principal loan amount now mean less interest you pay over the life of the loan.
  • Choose a shorter loan term. The longer you take to pay off your loan, the more interest you will end up paying. Remember, banks calculate interest on your loan amount daily, so choosing a 25-year loan term instead of 30 years can make a big difference to the amount of interest you pay overall.

5 tips to pay off your mortgage faster

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$
years
Name Product Interest Rate (p.a.) Comp. Rate^ Application Fee Ongoing Fees Max LVR Monthly Payment
Westpac Flexi First Option Home Loan
2.29%
2.72%
$0
$8 monthly ($96 p.a.)
95%
$577.55
Up to $3,000 refinance cashback.
A flexible and competitive variable rate loan. Eligible borrowers refinancing $250,000 or more can get $2,000 cashback per property plus a bonus $1,000 for their first application. Other conditions apply.
St.George Basic Home Loan
2.54%
2.56%
$0
$0 p.a.
80%
$596.91
Up to $4,000 refinance cashback. With this competitive variable rate loan from St.George, refinancers borrowing $250,000+ can get up $4,000 cashback and borrow up to 80% of the property's value. (Terms, conditions & exclusions apply).
HSBC Fixed Rate Home Loan
1.88%
2.98%
$0
$0 p.a.
80%
$546.6
Lock in a competitive fixed rate for 2 years and buy your home with a 20% deposit.
Macquarie Bank Basic Home Loan
2.49%
2.49%
$0
$0 p.a.
60%
$593.01
A competitive variable rate home loan for owner-occupiers. Requires a 40% deposit.
UBank UHomeLoan Variable Rate
2.34%
2.34%
$0
$0 p.a.
80%
$581.39
Enjoy flexible repayments, a redraw facility and the ability to split your loan. Plus, pay no application or ongoing fees.
Suncorp Back to Basics Home Loan
2.54%
2.55%
$0
$0 p.a.
80%
$596.91
A competitive variable interest rate loan with low fees. The establishment fee is waived if you borrow $150,000 or more.
Athena Variable Home  Loan
2.19%
2.19%
$0
$0 p.a.
60%
$569.91
Owner occupiers with 40% deposits or equity can get this competitive variable rate loan. No upfront or ongoing fees.
St.George Fixed Rate Advantage Package
2.09%
3.46%
$0
$395 p.a.
95%
$562.33
Lock in a low fixed rate for the first two years. Refinancers borrowing $250,000 or more can get cashbacks between $2,000 and $4,000 depending on their loan to value ratio (Other terms, conditions and exclusions apply
UBank UHomeLoan Fixed
1.95%
2.27%
$0
$0 p.a.
80%
$551.82
A competitive fixed interest rate loan with no ongoing fees. Requires a 20% deposit.
Suncorp Home Package Plus Fixed
1.89%
2.94%
$0
$0 p.a.
80%
$547.35
Lock in a low fixed rate loan for two years and get the annual package fee waived in the first year. Available for borrowers with 20% deposits.
Westpac Fixed Option Home Loan Premier Advantage Package
2.09%
3.5%
$0
$395 p.a.
95%
$562.33
Up to $3,000 refinance cashback.
Competitive fixed rate home loan. Eligible borrowers refinancing $250,000 or more can get up to $3,000 cashback. Other conditions apply.
HSBC Home Value Loan
2.59%
2.6%
$0
$0 p.a.
80%
$600.83
Get a low interest rate loan with no ongoing fees. Plus you can make extra repayments and free redraw online.
homeloans.com.au Low Rate Home Loan with Offset
2.14%
2.16%
$0
$0 p.a.
60%
$566.11
A competitive rate with no application or ongoing fee. This loan is not available for construction.
Virgin Money Reward Me Fixed Rate Home Loan
2.04%
2.79%
$300
$10 monthly ($120 p.a.)
80%
$558.56
$3,000 refinance cashback.
Buy your home and lock in a low rate for the first two years. Get a $3,000 cashback when you switch to Virgin Money with a loan amount of $300,000 or more with an LVR up to 80%. You must apply by 30 November 2020 and settle by 23 April 2021.
Macquarie Bank Offset Home Loan Package
2.49%
2.76%
$0
$0 p.a.
60%
$593.01
A sharp variable rate with low fees for borrowers with 40% deposits or refinancers with equity in their properties.
homeloans.com.au Low Rate Home Loan with Offset
2.24%
2.26%
$0
$0 p.a.
90%
$573.72
This loan offers a competitive variable rate and a 100% offset account to help save you on interest repayments. This loan is not available for construction.
St.George Basic Home Loan
2.59%
2.61%
$0
$0 p.a.
90%
$600.83
Up to $4,000 refinance cashback.
With this competitive variable rate loan from St.George, refinancers borrowing $250,000+ can get up $4,000 cashback and borrow up to 90% of the property's value. (Terms, conditions & exclusions apply).
Macquarie Bank Basic Fixed Home Loan
2.19%
2.53%
$0
$0 p.a.
80%
$569.91
Borrow up to $750,000 with this basic 3 years fixed rate home loan.
Bank of Melbourne Basic Home Loan
2.54%
2.56%
$0
$0 p.a.
80%
$596.91
Up to $4,000 refinance cashback
A competitive variable rate loan from Bank of Melbourne. Refinancers borrowing $250,000 or more can get $4,000 cashback (Other terms, conditions and exclusions apply).
UBank UHomeLoan Fixed
2.14%
2.35%
$0
$0 p.a.
80%
$566.11
Fix your mortgage for 1 year with a very competitive rate and no ongoing fees.
Bank of Melbourne Advantage Package Fixed Home Loan
2.09%
3.46%
$0
$395 p.a.
95%
$562.33
Competitive fixed rate loan. Refinancers borrowing $250,000 or more can get cashbacks between $2,000 and $4,000 depending on their loan to value ratio (Other terms, conditions and exclusions apply
BankSA Basic Home Loan
2.54%
2.56%
$0
$0 p.a.
80%
$596.91
Up to $4,000 refinance cashback
A competitive variable rate loan from BankSA. Refinancers borrowing $200,000 or more can get a $4,000 cashback (Other terms, conditions and exclusions apply).
homeloans.com.au Low Rate Home Loan with Offset
2.59%
2.61%
$0
$0 p.a.
90%
$600.83
Save on interest with a free 100% offset account and buy your property with just a 10% deposit. This loan is not available for construction.
Bank of Melbourne Basic Home Loan
2.59%
2.61%
$0
$0 p.a.
80%
$600.83
Competitive variable rate home loan. Refinancers borrowing $250,000 or more can get cashbacks between $2,000 and $4,000 depending on their loan to value ratio (Other terms, conditions and exclusions apply
BankSA Advantage Package Fixed Home Loan
2.09%
3.46%
$0
$395 p.a.
80%
$562.33
Competitive fixed rate loan. Refinancers borrowing $200,000 or more can get cashbacks between $2,000 and $4,000 depending on their loan to value ratio (Other terms, conditions and exclusions apply
Athena Variable Home  Loan
2.29%
2.23%
$0
$0 p.a.
80%
$577.55
A competitive variable rate mortgage for owner occupiers $0 application and $0 ongoing fees. This interest rate falls over time as you pay off the loan.
UBank UHomeLoan Variable Rate
2.74%
2.74%
$0
$0 p.a.
80%
$612.67
Get a discounted, low-fee investor loan from a convenient online lender. 20% deposit required.
Virgin Money Reward Me Variable Home Loan
2.59%
2.76%
$300
$10 monthly ($120 p.a.)
60%
$600.83
$3,000 refinance cashback.
A variable rate loan for owner occupiers with a 40% deposit (or equity) borrowing under $500,000. Get a $3,000 cashback when you switch to Virgin Money with a loan amount of $300,000 or more with an LVR up to 80%. You must apply by 30 November 2020 and settle by 23 April 2021.
Athena Variable Home  Loan
2.24%
2.21%
$0
$0 p.a.
70%
$573.72
A low variable rate for owner occupiers with 30% deposits. No upfront or ongoing fees.
UBank UHomeLoan Fixed
2.29%
2.35%
$0
$0 p.a.
80%
$577.55
A competitive 3 year fixed rate with no ongoing bank fees.
Macquarie Bank Basic Fixed Home Loan
2.09%
2.43%
$0
$0 p.a.
70%
$562.33
Get a low interest rate and a mortgage with flexible, basic features. No application or ongoing fees. Requires a 30% deposit.
UBank UHomeLoan Fixed
2.29%
2.36%
$0
$0 p.a.
80%
$577.55
A one year fixed rate offer with no ongoing bank fees.
Athena Variable Home  Loan
2.84%
2.46%
$0
$0 p.a.
80%
$620.63
Owner occupiers can refinance to one of the most competitive interest-only rates in the market. No application fee and no ongoing fees.
UBank UHomeLoan Fixed
2.44%
2.74%
$0
$0 p.a.
80%
$589.12
Investors can enjoy flexible repayments and an easy application process with this pioneering online lender.
Well Home Loans Balanced Fixed Home Loan
1.94%
2.18%
$250
$0 p.a.
90%
$551.07
Owner occupiers can get a sharp fixed rate for the first year, plus an offset account. Available with a 10% deposit.
Well Home Loans Balanced Fixed Home Loan
2.04%
2.17%
$250
$0 p.a.
90%
$558.56
A low 3 year fixed rate for home buyers. Add a 100% offset account with a $10 monthly fee. Not available for construction purposes.
Well Home Loans Balanced Fixed Home Loan
1.99%
2.17%
$250
$0 p.a.
90%
$554.81
A low fixed mortgage with an optional 100% offset account. Not available for construction purposes.
HSBC Home Value Loan
2.64%
2.65%
$0
$0 p.a.
90%
$604.76
A competitive value home loan with no ongoing fee.
Macquarie Bank Basic Home Loan
2.64%
2.64%
$0
$0 p.a.
80%
$604.76
Pay no application and ongoing fees and take advantage of split and redraw options.
UBank UHomeLoan Fixed
2.29%
2.72%
$0
$0 p.a.
80%
$577.55
Investors can enjoy flexible repayments and an easy application process with this pioneering online lender.
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Westpac Flexi First Option Home Loan - Basic Variable Rate (Owner Occupier, P&I)

Up to $3,000 refinance cashback. A flexible and competitive variable rate loan. Eligible borrowers refinancing $250,000 or more can get $2,000 cashback per property plus a bonus $1,000 for their first application. Other conditions apply.

Logo for St.George Basic Home Loan - LVR 60% to 80% (Owner Occupier, P&I)
St.George Basic Home Loan - LVR 60% to 80% (Owner Occupier, P&I)

Up to $4,000 refinance cashback. With this competitive variable rate loan from St.George, refinancers borrowing $250,000+ can get up $4,000 cashback and borrow up to 90% of the property's value. (Terms, conditions & exclusions apply).

Logo for Athena Liberate Home Loan - 70% to 80% LVR Owner Occupier, P&I
Athena Liberate Home Loan - 70% to 80% LVR Owner Occupier, P&I

A competitive variable rate mortgage for owner occupiers $0 application and $0 ongoing fees. This interest rate falls over time as you pay off the loan.

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Suncorp Back to Basics Home Loan - Better Together Special Offer $150k+ LVR ≤ 80% (Owner Occupier, P&I)

Get a competitive variable interest rate with no application fee or ongoing fees.

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