Down Payment Tool
Explore home purchase deposits as amounts or percentages, then estimate the mortgage balance, monthly repayments, upfront cash requirements and insurance. Compare your current savings with the goal, forecast a target date and review yearly amortisation.
| Year | Principal paid | Interest paid | Remaining balance |
|---|
Estimates for planning only. Mortgage insurance is illustrative and may depend on location, loan type and lender. Taxes, home insurance, maintenance and changing rates are excluded from monthly mortgage figures.
Table of Contents
Highlights
- Compare percentage-based and fixed-amount deposits with quick presets.
- Estimate monthly mortgage repayments, total interest and loan-to-value.
- Include closing costs, upfront extras and optional mortgage insurance.
- Track savings progress and forecast target-month contributions.
- Explore interactive charts, annual amortisation and CSV or JSON exports.
How Down Payment Tool Works?
The home deposit can be specified as a percentage of the purchase price or as a fixed amount. The mortgage principal is the price less the deposit, and loan-to-value (LTV) is the financed share of the property price.
Here, P is the purchase price, D is the deposit, d is the deposit percentage and L is the mortgage principal. The fixed-rate monthly principal-and-interest payment follows the standard amortising loan formula, with a separate calculation for a zero interest rate.
M is the monthly repayment, i is the entered annual mortgage interest rate in percent, and t is the loan term in years. When r is zero, M = L ÷ n. The yearly mortgage schedule adds each month's interest (outstanding balance × r) and principal paid (payment less interest); total interest is the sum of monthly interest charges.
| Output | Calculation |
|---|---|
| Total upfront cash | Deposit + purchase price × closing cost percentage ÷ 100 + other upfront costs |
| Estimated monthly mortgage insurance | If enabled and deposit is below 20%: mortgage principal × annual insurance percentage ÷ 1200; otherwise zero |
| Monthly repayment including insurance | Monthly principal-and-interest payment + estimated mortgage insurance |
| Savings still required | Greater of zero and total upfront cash less current savings |
| Funding progress | Current savings ÷ upfront cash × 100%, capped at 100% |
For the savings forecast, the current balance earns one month's assumed return before that month's savings contribution is added. This process repeats until the upfront cash goal is met, up to 1,200 months. If a target month is entered, the tool also tests whether that date is achievable and estimates the required monthly contribution using the future value of existing savings and a series of end-of-month contributions.
S is the savings balance, C is the monthly savings contribution and a is the assumed annual savings return in percent. The funding mix bar, savings progress bar, mortgage balance chart and yearly amortisation table illustrate these results. Available exports include a summary CSV, an annual amortisation CSV and detailed JSON.
Practical Use Cases
First-time homebuyers: Compare 3.5%, 5%, 10% and 20% deposits to see how much cash you need at purchase and how the mortgage size changes.
Households saving for a deposit: Enter current savings, a monthly contribution and an assumed return to estimate the remaining savings gap and the month in which the upfront cash target may be reached.
Buyers working towards a deadline: Set a target purchase month to check whether planned contributions are enough or to estimate the monthly savings required to meet that date.
Home movers and repeat buyers: Add closing costs and other upfront expenses to budget for the full cash requirement, rather than the deposit alone.
Mortgage comparison shoppers: Adjust the rate, term and deposit to examine estimated monthly repayments, LTV, lifetime interest and the mortgage balance over successive years.
Buyers considering smaller deposits: Turn on illustrative mortgage insurance to see how a deposit below 20% can affect the estimated monthly outlay.
Accuracy and Limitations
Results follow the entered figures and standard fixed-rate, monthly amortisation mathematics, with currency amounts rounded for display. The forecast assumes a constant mortgage rate, regular payments, a constant savings return and end-of-month deposits; it does not model mortgage rate changes, taxes, property insurance, maintenance, affordability tests, lender fees beyond the amounts entered, or changes in house prices. Mortgage insurance is a simple annual percentage of the original loan, charged monthly only when enabled and the deposit is below 20%; it does not automatically cease as equity increases. Savings reachability is checked for a maximum of 1,200 months. Actual lender criteria, insurance pricing and closing charges vary by location and product.
