Useful next calculations
When to use this calculator
- Before comparing mortgage products, brokers or repayment types.
- When you want to test how a different deposit, rate or term changes the payment.
- When you need a quick estimate before using a formal illustration or agreement in principle.
- When you are stress-testing your budget against a higher rate.
A worked example
These are the example figures the calculator opens with.
| Input | Value |
|---|---|
| Remaining Balance ($) | $180,000 |
| Interest Rate (%) | 5.5% |
| Remaining Term (Years) | 20 years |
| Monthly Overpayment ($) | $200 |
For those figures the calculator returns:
- Current payment: $1,238.20
- Payment with monthly overpayment: $1,438.20
- Payoff term: 15.00 years 7.00 months
- Months saved: 53.00
- Interest saved: $29,062.14
Method & assumptions
This calculator compares a baseline repayment projection with a plan that adds the monthly and one-off overpayments you enter. It keeps the calculated contractual repayment constant and applies the one-off amount before the monthly projection; the payoff term and interest saving are therefore estimates rather than instructions to your lender. A lender may instead reduce your required payment, credit an overpayment at a different point, or apply product-specific rules.
The projection assumes a constant interest rate and does not model early repayment charges, rate changes, payment holidays, offsets or fees. Check your lender's overpayment allowance, any early repayment charge and how it will apply a lump sum before paying.
Common mistakes
- Mixing up loan amount and property value, which distorts affordability and LTV.
- Using a headline rate but forgetting fees, insurance or repayment type.
- Testing only one term length instead of comparing payment and total cost together.
- Treating the result as a lender decision rather than a planning estimate.
What to do next
- Run a second scenario with a cautious assumption so you can see the downside clearly.
- Compare the result with the related calculators below before making a decision.
- Check current local rules, eligibility and provider terms before applying or committing money.
- Keep a record of the assumptions so you can update the estimate when a quote, bill or pay figure changes.