Mortgage Calculator
Estimate principal-and-interest repayments from property price, deposit, rate and term.
Use the Mortgage Calculator
Estimate principal-and-interest repayments from property price, deposit, rate and term.
Calculations happen locally in your browser. ToolLott does not send these inputs to a server for this tool.
This is a general financial estimate based only on the values you enter. It does not include product fees, changing rates, taxes or jurisdiction rules unless you enter them explicitly, and it should not be the sole basis for a financial decision.
How to use it
Enter the assumptions you want to test, then calculate. No live rates or jurisdiction-specific tax rules are fetched.
How the Mortgage Calculator works
The Mortgage Calculator estimates the monthly principal-and-interest repayment for a loan after subtracting the deposit from the property price.
Calculation breakdown
ToolLott will explain the current inputs and displayed result here.
Mortgage repayment formula and assumptions
ToolLott uses the standard amortising-loan payment equation. The annual percentage rate is converted to a monthly rate and the loan term is converted to a number of monthly payments.
P = Property price - DepositP is the amount borrowed before any fees not entered in the tool.
M = P x [r(1+r)^n] / [(1+r)^n - 1]r is the monthly interest rate and n is the number of monthly repayments.
| Symbol / input | Meaning | Unit |
|---|---|---|
P | Loan principal | currency |
r | Monthly interest rate (annual rate / 12) | decimal |
n | Number of monthly repayments | months |
M | Estimated monthly principal-and-interest repayment | currency/month |
Step-by-step method
- Subtract the deposit from the property price to get the loan amount.
- Convert the annual interest rate to a monthly decimal rate.
- Multiply the loan term in years by 12 to get the number of monthly payments.
- Apply the amortising-loan equation and calculate total interest from repayment x number of payments minus principal.
Worked example
A buyer is considering a AUD 650,000 property with a AUD 130,000 deposit, a 6.15% annual rate and a 30-year principal-and-interest term.
Example inputs
- Property price = AUD 650,000
- Deposit = AUD 130,000
- Annual rate = 6.15%
- Term = 30 years
Calculation / processing
Loan principal = 650,000 - 130,000 = AUD 520,000Monthly rate = 6.15% / 12 = 0.5125%Number of payments = 30 x 12 = 360Amortising-loan formula gives approximately AUD 3,167.99 per month
At the entered constant rate, 360 monthly repayments total about AUD 1,140,475, of which about AUD 620,475 is interest. Real home-loan costs can differ because rates, fees and repayment timing can change.
Assumptions
- Principal-and-interest repayments are modelled monthly.
- The entered interest rate is assumed constant for the calculation.
- No establishment fees, ongoing fees, offset-account effects, redraws or extra repayments are included unless another ToolLott tool explicitly models them.
Limitations
- This is a modelling estimate, not a loan offer or prediction of future rates.
- Lender calculation conventions and repayment frequencies can produce slightly different figures.
- Affordability also depends on income, expenses, fees, taxes, insurance and lender criteria that are outside this calculator.
Common questions
Why can a small rate change affect repayments so much?
The rate applies over many payment periods. A higher rate increases each repayment and the cumulative interest paid across the term.
Does this calculator include lender fees?
No. The flagship calculation models principal and interest from the entered loan amount, annual rate and term.
Is the result a borrowing recommendation?
No. It is a numerical repayment estimate. Borrowing suitability and approval depend on the lender and the borrower's circumstances.
Methodology sources
Related ToolLott tools
A realistic way Grace could use this tool
Grace is a first-home buyer comparing loan scenarios.
Grace is considering a AUD 650,000 property with a AUD 130,000 deposit and wants to test a 6.15% principal-and-interest loan over 30 years before making an offer.
They use the worked values shown in the tool: Currency code: AUD; Property price: 650000; Deposit: 130000; Annual interest rate (%): 6.15; Loan term (years): 30.
ToolLott returns “Estimated monthly mortgage repayment: AUD 3,167.99”. That gives Grace a concrete figure to check against the real task before they copy it into the next document or decision.
Fictional scenario using realistic example data. For Ready tools, the worked result is tied to the tested example shown in the tool. Replace the figures with your own inputs and independently verify important professional, financial, legal, health or safety decisions.
What this calculator is for
Use it to estimate principal-and-interest repayments from property price, deposit, rate and term.
It sits within ToolLott’s Personal & Business Finance collection, where you can also estimate compound and simple interest, EMI, loans, mortgages, retirement savings, salary, tax and GST/VAT.