See the real cost of your mortgage.
Calculate repayments, stress-test a higher rate, see what extra payments could save, or work out what it may take to clear your mortgage earlier.
Build your mortgage scenario
Principal-and-interest mortgage modelling with flexible repayment scenarios.
CalcNest AI Analysis
Ask about your mortgage, test another scenario, or understand what is driving the result.
What does a mortgage calculator tell you?
A mortgage calculator turns a loan amount, interest rate and term into an estimated principal-and-interest repayment. CalcNest goes further by showing the lifetime interest cost, amortisation path and how changing the rate, making extra repayments or choosing an earlier payoff target can affect the loan.
Your regular repayment
Estimate the principal-and-interest payment required to repay the mortgage over the selected term at the entered rate.
Your lifetime interest
See how much interest could be paid if the rate remained unchanged and the mortgage followed the calculated repayment schedule.
The effect of paying extra
Compare the standard schedule with additional repayments to estimate the interest and time that could be saved.
How mortgage repayments are calculated
For a standard principal-and-interest mortgage, each repayment covers the interest charged for that period and pays down part of the principal. The payment is set so the balance reaches zero at the end of the chosen term, assuming the rate stays unchanged.
P is the mortgage principal, r is the interest rate per repayment period, n is the total number of repayments and M is the regular repayment.
Worked example
Suppose you borrow 500,000 for 30 years at 6% a year with monthly principal-and-interest repayments.
Why can mortgage interest become so large?
Interest is charged on the outstanding balance. Early in a long mortgage the balance is still high, so a larger share of each repayment goes toward interest. As principal falls, the interest charge falls too and more of the payment can reduce the balance.
The balance is high, so interest makes up a larger part of the repayment.
The balance has fallen and the principal portion becomes increasingly important.
Less interest is charged because much less principal remains outstanding.
Rate and term can change the result dramatically
Using the same 500,000 mortgage, changing only the interest rate or term can materially change both the regular repayment and lifetime interest. This is why a useful mortgage plan should test more than one scenario.
| Scenario | Approx. monthly repayment | Approx. lifetime interest | What changes? |
|---|---|---|---|
| 5% for 30 years | 2,684 | 466,000 | Lower rate |
| 6% for 30 years | 2,998 | 579,000 | Baseline |
| 7% for 30 years | 3,327 | 698,000 | Higher rate |
| 6% for 20 years | 3,582 | 360,000 | Shorter term |
How extra mortgage repayments can save interest
An additional repayment reduces principal sooner. That can reduce future interest because subsequent interest is calculated on a smaller balance. The effect compounds across the remaining mortgage term.
Regular extra repayments
A consistent amount on top of the required repayment can shorten the payoff period and reduce total interest.
Lump-sum payments
A bonus, refund or other lump sum applied to principal can reduce the balance immediately, subject to your mortgage terms.
Earlier payoff target
CalcNest can work backwards from a shorter term to estimate the extra regular payment required to reach it.
Your mortgage repayment may not be your total housing cost
CalcNest's global mortgage engine focuses on principal and interest. Depending on the country, property and loan, your actual housing costs may also include taxes, insurance, mortgage insurance, strata or association charges, lender fees and purchase or closing costs.
Property costs
Taxes, insurance, maintenance and building or association charges can sit outside the principal-and-interest calculation.
Loan costs
Application, valuation, account, mortgage-insurance or other lender charges vary by product and market.
Changing rates
A variable or adjustable rate can change future repayments. Use the Rate Stress Test to explore alternatives rather than assuming today's rate lasts forever.
Offset accounts, redraw and repayment frequency
Offset and redraw
Some mortgage products let cash held in an offset account reduce the balance used to calculate interest, while redraw facilities may let borrowers access eligible extra repayments later. Availability, fees and access rules vary between lenders and countries, so CalcNest does not treat either feature as universal.
Weekly, fortnightly or monthly?
Changing repayment frequency does not automatically guarantee a saving. The outcome depends on how the lender calculates the required payment. For example, paying half a monthly repayment every two weeks creates 26 half-payments in a year — equivalent to 13 monthly payments — which is different from simply recalculating the same annual repayment across 26 periods.
Buying property across borders?
If a property purchase involves moving a deposit, sale proceeds or another large amount between currencies, the exchange rate and transfer fee can affect how much reaches the destination. Wise supports international large-amount transfers, including transfers connected with property purchases.
Affiliate disclosure: CalcNest may earn a commission if you use an eligible Wise link, at no extra cost to you. Always compare the rate, fee and suitability for your transfer.
Related CalcNest tools
A mortgage is only one part of a wider financial plan. These tools can help you explore the surrounding decisions.
Mortgage calculator FAQs
How accurate is a mortgage calculator?
What is principal and interest on a mortgage?
Why is so much of a mortgage payment interest at the beginning?
Can total mortgage interest be more than the amount borrowed?
Does paying extra on a mortgage save interest?
Is a shorter mortgage term always better?
What does LTV mean?
What happens to my mortgage payment if interest rates rise?
Does this mortgage calculator include taxes, insurance and fees?
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