Home Loan Calculator
Work back from a property price and deposit to the loan, its lifetime interest cost and what overpaying saves.
Please note: An estimate, not a lending decision. The rate you are offered depends on your deposit, credit assessment and the lender’s criteria, and legal, valuation and transfer costs sit outside this calculation.
What the Home Loan Calculator does
A home loan is the largest and longest borrowing most people take on, and the number that matters is rarely the monthly one. This calculator starts where a purchase actually starts — a property price and the deposit you have — and works forward to the loan you need, the loan-to-value that will decide the rate band you are offered, and what the borrowing costs across its whole life. Because the term is long, overpayment has an outsized effect, so it also shows how much sooner the loan clears and how much interest disappears when you pay more than the instalment.
Formula
Loan = property price − depositLTV = loan ÷ property price × 100Instalment = P × r × (1 + r)ⁿ ÷ ((1 + r)ⁿ − 1), r = annual rate ÷ 12 ÷ 100, n = tenure in monthsOverpayment is simulated month by month: each extra payment reduces principal, so all future interest on it is never charged
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Property price | selected currency | Yes | Accepts more than 0. |
| Deposit given as | one of 2 options | Yes | — |
| Deposit | selected currency or % | Yes | Accepts more than 0. |
| Annual interest rate | % | Yes | — |
| Tenure | years | Yes | Accepts 1 or more, up to 40. |
| Extra paid each month | selected currency | Optional | Regular overpayment above the instalment. Accepts 0 or more. |
| One-off lump sum | selected currency | Optional | A single extra payment, for example a bonus. Accepts 0 or more. |
| Paid in year | number | Optional | Accepts 1 or more, up to 40. Shown in no standard mode. |
| Currency | one of 10 options | Optional | — |
How to use it
- Choose Deposit given as and Currency.
- Enter Property price, Deposit, Annual interest rate and Tenure.
- Fill in the remaining inputs the form shows for your choice.
- Optionally add Extra paid each month and One-off lump sum.
- Select Calculate.
Worked example
A $300,000 property with a 20% deposit over 20 years at 6%, overpaying $200 a month.
- Price
- 300000
- Deposit
- 20
- Rate
- 6
- Tenure
- 20
- Overpay
- 200
A $240,000 loan at 80% LTV, $1,719.43 a month, $172,664.29 of interest over 20 years. Overpaying $200 clears it in 16 years 5 months and saves $35,006.35.
Frequently asked questions
What does loan-to-value change?
LTV is the loan as a percentage of the property price, and lenders band their pricing by it. Because the bands are steps rather than a slope, a deposit that takes you from just above a threshold to just below it can move you into a cheaper band — which is worth checking before rounding your deposit down. This calculator shows the LTV your deposit produces; which bands exist and what they cost differs by lender and country.
How much does overpaying actually save?
More than the overpayment itself, because every extra unit of principal repaid cancels all the future interest that principal would have accrued. On a long loan that compounding runs for decades, which is why a modest monthly overpayment can remove years. Enter one above to see the effect on your own figures.
Is a lump sum better early or late?
Early, and by a wide margin. A lump sum paid in year two avoids interest on that amount for the remaining term; the same sum paid in the final years avoids very little, because most of the interest has already been charged. Move the year field to compare.
Why does a small rate difference matter so much here?
Because the balance is large and the term is long. A quarter-point applies to hundreds of payments on a balance that stays high for years, so a difference that looks trivial monthly is substantial in total. The total interest figure above is the one to compare between offers.
How is this different from the mortgage calculator?
This one is about the loan across its whole life — what you need to borrow, what it costs in total, and what overpaying changes. The mortgage calculator answers a different question: what leaves your account each month once property tax, insurance and any service charge are added to the instalment. Use that one for budgeting, this one for the cost of the borrowing.
Method and sources
Method. The standard amortizing-loan formula for the instalment; overpayment is simulated month by month, reducing principal directly so every future interest charge on that amount is never accrued — not estimated from a lump-sum shortcut.
Assumptions
- The loan-to-value figure is simple arithmetic (loan ÷ price); it does not model any specific lender’s rate bands, which vary by lender and by LTV threshold.
- An overpayment is assumed to reduce the term rather than the instalment, and to be accepted immediately and in full.
Limitations
- Legal, valuation, survey and transfer costs — real costs of buying a home — are outside this calculation entirely.
- Some lenders cap annual overpayments or charge for them; this calculator has no way to know your specific loan’s terms.