Australia methodology

How each Australian estimate is sourced and calculated.

This page brings together the formulas, official sources, assumptions and review dates used by the Australian calculators.

Calculation basis

Calculator methods and sources

Income Tax, LITO, Medicare, MLS and HELP

Resident income tax is the sum of each progressive FY 2026–27 band. LITO then reduces income tax but cannot create a refund. HELP uses repayment income and the 2026–27 marginal system; the result is capped at the outstanding debt entered.

Medicare status: the calculator uses the A$28,011 threshold and A$35,013 phase-in endpoint in the official 2026 PAYG withholding schedule. It applies 10% of income above the lower threshold during phase-in, capped at the ordinary 2% levy. The page labels this as a PAYG Schedule-derived estimate and is scheduled for review when the FY 2026–27 annual assessment threshold is published.

MLS models a full-year single person with full-year approved-hospital-cover selection. The rate tier uses taxable income plus surcharge-base and tier-only additions; the selected rate is applied to taxable income plus surcharge-base additions. Family or partial-year cases can be checked with the ATO assessment guidance.

Mortgage and offset

The default 6.15% rate is the RBA average for new owner-occupier principal-and-interest housing loans in May 2026. The contractual repayment uses M = P × r(1+r)ⁿ ÷ ((1+r)ⁿ − 1). Each simulated month charges interest on max(loan balance − offset balance, 0), then applies the contractual payment and any extra payment. The offset balance itself does not repay principal. This is a monthly approximation; lenders commonly calculate interest daily.

Superannuation

The default 6.1% return follows ASIC Moneysmart's Balanced investment-option default current at June 2026. The projection starts with 12% SG on the entered FY 2026–27 qualifying earnings up to the A$270,830 maximum contribution base. Employer and salary-sacrifice contributions are reduced by 15% contributions tax. Return means after investment tax, before the fees and insurance entered, so fees are deducted once.

The current A$32,500 concessional cap, A$130,000 ordinary non-concessional cap, A$2.1 million transfer balance cap and maximum contribution base are projected forward using the disclosed salary-growth or inflation assumption; actual statutory indexation may differ. After-tax contributions use the modelled ordinary cap and pause for a model year when its opening balance reaches the modelled transfer balance cap. Dollar administration fees and insurance increase with inflation. The result represents an accumulation-account scenario; ATO and fund guidance supplies personalised cap, defined-benefit and retirement treatment.

Car loan and balloon

The default 10.42% rate is the RBA F8 May 2026 average for new fixed-rate personal fixed-term loans, used as an editable planning reference. A balloon is discounted back over the loan term and the remaining principal is amortised into equal monthly repayments. The establishment fee is added to principal. The monthly account fee is added to cash flow. Weekly and fortnightly figures are monthly budget equivalents; the lender schedule supplies contractual dates.

GST and compound interest

GST-exclusive arithmetic uses gross = net × 1.10. For a GST-inclusive amount, GST = gross ÷ 11. ATO guidance determines the GST classification of the supply.

The default compound-interest rate is the RBA F4.1 average paid on new household term deposits in May 2026: 4.6%. Compound interest uses monthly compounding and month-end contributions. Weekly, fortnightly and yearly contribution inputs are converted to annual amounts using 52, 26 and 1 payments, then divided into 12 monthly-equivalent deposits. The result is a monthly budgeting scenario.

Editable inputs

Reference interest rates, offset balances, extra repayments, salary growth, investment return, fees, insurance, inflation and contribution amounts can be replaced with the figures for the scenario being compared. Statutory settings remain tied to FY 2026–27.

Review dates

• ATO or legislation changes FY 2026–27 resident rates, LITO, HELP/STSL or Medicare thresholds.
• Super Guarantee, qualifying-earnings rules, concessional/non-concessional caps, transfer balance cap or maximum contribution base changes.
• The statutory GST rate changes.
• A formula defect or conflicting benchmark is reported.

Last verified: 18 July 2026. See the contact page to report a discrepancy.

Using the estimates

Use each result as a planning scenario, then confirm the relevant amount with an ATO assessment, fund statement, lender schedule or transaction record.