Calculator assumptions and methodology
How the Nest Invest AU calculators build your scenario. The assumptions in use are shown alongside your results.
Retirement income and spending
Weekly and annual spending are linked by 52 weeks, and the last field you edit takes priority. The calculator can start with a spending target based on a share of household income; your own entry replaces it. Spending in the first year of retirement is A = annual spending × (1 + inflation)^years until retirement.
Required retirement balance
For end-of-year withdrawals, required capital is A × [1 − ((1 + inflation) ÷ (1 + retirement return))^years in retirement] ÷ (retirement return − inflation). When the two rates are equal, this becomes A × years in retirement ÷ (1 + inflation). Start-of-year withdrawals multiply the result by (1 + retirement return). Retirement must last at least one year.
Assets, super and regular savings
Current funds combine both super balances, savings, shares, net investment property equity and other retirement assets. Estimated first-year employer contributions equal combined gross income × the employer super rate × (1 − contribution tax). At a 12% super rate and 15% contribution tax, $100,000 of income adds $10,200 a year. Employer contributions grow with inflation as a wage-growth assumption. Each year, contributions are added and investment returns are applied. The rates in use are listed with your results. Contribution caps, ordinary-time earnings rules, Division 293 tax and low-income tax offsets are not included.
Existing and additional savings
Your current weekly savings × 52 are added each year. Any remaining shortfall is converted into the additional annual saving needed, then divided by 52 for a weekly amount. The total weekly target includes your current savings, and the extra amount is what is needed on top of them. If no saving years remain, only the lump-sum gap is shown.
Today’s dollars and future dollars
Future-dollar mode shows the nominal balance at retirement. Today-dollar mode divides retirement-date values by (1 + inflation)^years until retirement. Each schedule balance is deflated at its own year end. Contributions required to start saving now remain current starting amounts. Percentage covered is projected capital divided by required capital, capped at 100%. A zero target has no coverage assessment.
Retirement outlook and limitations
The timeline applies the same contribution and withdrawal timing as the results. It identifies the first retirement year in which available funds cannot meet the planned withdrawal, and the schedule shows any unmet need in those years. The target-funded line starts at the capital needed at retirement. Returns are constant assumptions after investment fees and earnings tax, not forecasts. Age Pension, super access rules, minimum pension rules, insurance, asset sale costs, changing tax and market volatility are not included. Property equity is treated as available capital, which may require a sale.
Home loan repayment model
Interest is calculated daily on the loan balance less any eligible offset balance, using the annual rate ÷ 365, and is charged on each repayment date. During an interest-only period the interest-only rate applies and repayments cover interest only; the main rate applies afterwards. Principal-and-interest repayments are calculated from the same calendar dates and daily rates as the schedule, so the loan without changes is repaid by the end of the term. Monthly repayments keep the same day of the month where possible. Weekly and fortnightly repayments occur every 7 or 14 days, with a shorter final period if needed. Extra repayments do not reduce the scheduled repayment, so the loan is repaid sooner. Results can differ slightly from a simple textbook calculation and from a lender’s figures. Fees are paid separately and are not added to the loan.
Cashflow order, offsets and card expenses
By default, repayments, extra repayments and fees are paid from money outside the offset, so an opening offset balance stays in the offset. When you add income, the calculator switches to paying them from the offset account, and you can change this choice at any time. When paying from the offset, enter the take-home income deposited into it and include your living expenses, without entering loan repayments again as an expense. When paying from separate money, enter only cash left over after repayments and living costs. If the offset cannot cover a payment, the shortfall is shown as additional cash needed from elsewhere; the offset never goes below zero. Card expenses are delayed by a fixed number of days and assumed to be paid in full. Card interest, card fees and statement cycles are not modelled.
Dates, results and schedules
Monthly events keep the same day of the month where possible, falling on the last day in shorter months. Weekly and fortnightly events repeat every 7 or 14 days. Recurring cashflows can have a start date, end date or number of occurrences, and one-off cashflows occur once. Interest saved compares total loan interest, total cost saved also includes ongoing fees, and time saved compares payoff dates. First fully offset is the first date the eligible offset balance covers the loan and accrued interest; the loan is still owing and later spending can restart interest. Loan paid off is the date the debt is actually repaid. Amounts are calculated at full precision and shown to the cent. Downloaded and printed results list your inputs and the method used.
Your information and this estimate
Calculations run in your browser, and you do not need to submit a form to see results. Your inputs are kept in this browser tab until you press Reset or close the tab, and contact details are never stored there. Nothing is sent to Nest Invest AU unless you submit an enquiry, and your calculator scenario is included only if you choose to share it. General information only. This calculator does not consider your objectives, financial situation or needs and is not financial, credit or tax advice. Results are estimates based on the assumptions shown, not a guarantee or a lender quote. Consider obtaining advice from an appropriately licensed professional before acting.
Further reading
Property finance tools
The four property-finance tools use the dated rate set and configurable assessment assumptions shown with each result.
Borrowing capacity
Australian resident income tax is calculated separately for each applicant using the configured marginal bands. A flat Medicare levy assumption is included; low-income levy reductions, Medicare levy surcharge, tax offsets and deductions are excluded. HELP uses marginal repayment-income bands, capped at the configured share of total repayment income. Other reportable income can be entered as HELP additions. Rental and other income are taxed in full for this simplified model and then reduced by the assessment shading percentage. Available monthly income is net assessed income less the higher of declared living expenses or the illustrative household floor, special expenses, retained rent, debt repayments, credit-card limit commitments and a reserve. Borrowing capacity is the present value of available repayments at the higher of product rate plus buffer or assessment floor. An interest-only period reduces the amortising assessment term. DTI is an indicator, not an individual approval ceiling. This tool does not reproduce any lender panel or licensed household-expenditure benchmark.
Purchasing power and LMI
For each candidate price the model calculates duty, fees, cash reserved and any entered LMI quote. Funds available for the property deposit equal savings plus non-repayable gift plus a confirmed grant available at settlement, less buying costs, retained cash and upfront LMI. The base loan is price less deposit; capitalised LMI is then added once. The result must satisfy both borrowing and total loan-to-value limits. Each duty bracket and concession boundary is searched separately. LMI is a customer-entered estimate, not an insurer tariff. Grants and federal guarantee eligibility are not assessed automatically.
Transfer duty
The selected state table uses the greater of purchase price and market value. Duty may use a marginal band, a whole-value rate, or the Northern Territory quadratic formula below its upper threshold. The configured rounding unit applies before the bracket rate. A concession applies only when the visitor requests it and confirms the official eligibility conditions. The tool covers residential established and new homes, not vacant land, mixed-use property, trusts, fractional transfers or specialised off-the-plan concessions. Foreign purchaser surcharge is calculated on the entered subject share. Registration and professional fees are entered allowances. Official assessment and rounding may differ. Tasmania’s expired established-home exemption is not applied to the supplied 2026–27 rate period.
Refinance comparison
Refinance comparison uses monthly nominal interest with constant offset balances, unlike the daily-calendar cashflow model in the home loan repayment tool. Payment = principal × monthly rate ÷ (1 − (1 + monthly rate)^−months); at zero interest, payment is principal ÷ months. Monthly interest is charged on max(balance − offset, 0). Both schedules include entered monthly fees. Switching costs are either paid upfront or added once to new principal. Cashback arrives in the configured month. Cashflow benefit equals cumulative current payments and fees less new payments and fees, upfront costs, plus received cashback. Economic benefit also adds current remaining debt and subtracts new remaining debt. First break-even is the first non-negative monthly benefit and may not persist. Lifetime cost comparisons deduct switching costs once.
Rate governance and privacy
Calculator Studio stores the input defaults, supported rules, rate tables, source links and review dates. Dates outside the loaded legal-rate period produce a notice instead of using an unverified table. Every saved revision is archived. Calculations run in the browser. Inputs stay in session storage in the current tab; contact details do not. Only a submitted enquiry is stored, and sharing the calculator snapshot is optional. Shared snapshots are customer-supplied estimates and must be verified before use.