The short answer
Australia does not use joint tax filing — you and your spouse each lodge your own return and pay tax at your own marginal rate, no matter what your partner earns. The tax return still asks for spouse details because a handful of specific items are tested on combined family income, not your income alone: the Medicare Levy Surcharge (MLS), the private health insurance rebate, the tax offset for super contributions to a low-income spouse, and — through Services Australia rather than the ATO (ATO guidelines) — Family Tax Benefit and Child Care Subsidy reconciliation. A de facto partner, married or not, same-sex or opposite-sex, is treated exactly the same as a legally married spouse for every one of these tests. Get the spouse section wrong and the consequence isn't a joint tax bill; it's a recalculated surcharge, rebate, or family-payment debt landing on one or both of you later.
Why the tax return asks for spouse details, even without joint filing
The "Spouse details – married or de facto" section exists purely to calculate family-income-tested items. None of them change your tax bracket. Here's what each one actually does with the number.
Medicare Levy Surcharge (MLS)
The MLS is an extra 1%–1.5% levy on your income if you don't hold private hospital cover and your income is above the threshold — and that threshold roughly doubles once you have a spouse. Figures below are the FY2025–26 thresholds (1 July 2025 – 30 June 2026); the ATO indexes most of them most years, so check the current-year table if you're reading this later.
| Income tier | Singles threshold | Family/couple threshold | Surcharge rate (no hospital cover) |
|---|---|---|---|
| Base tier | $101,000 or less | $202,000 or less | 0% |
| Tier 1 | $101,001–$118,000 | $202,001–$236,000 | 1% |
| Tier 2 | $118,001–$158,000 | $236,001–$316,000 | 1.25% |
| Tier 3 | $158,001 or more | $316,001 or more | 1.5% |
*Family thresholds increase by a further $1,500 for each dependent child after the first.*
The mechanism matters here: MLS is assessed on combined income, so a spouse's income can push a couple over a threshold that neither individual would cross alone — or, just as often, a lower-earning spouse keeps the household under a threshold that would otherwise apply if MLS were worked out on the higher earner's income by itself. Example: one partner earns $115,000 (above the $101,000 single base tier) and the other earns $30,000. Assessed as a family, combined income is $145,000 — still under the $202,000 family base tier, so no MLS applies, provided the couple has appropriate hospital cover or knowingly accepts the surcharge outcome. Without declaring the spouse, the return has no way to apply the correct — and higher — family threshold.
Private health insurance rebate
The government rebate on private health premiums uses the same income tiers as the table above, but works in the opposite direction: the rebate percentage steps down as income rises, based on the age of the oldest person covered by the policy. A couple's rebate is calculated on their combined income against the family thresholds, not on each partner's income against the singles thresholds — which is exactly why a family/couple policy and a singles policy at a similar premium can carry different rebate percentages for otherwise comparable households.
Tax offset for super contributions to your spouse
If you contribute to your spouse's superannuation and their assessable income (plus reportable fringe benefits and reportable super contributions) is $37,000 or less, you may be able to claim a tax offset of up to $540 — 18% of contributions up to $3,000. The offset phases out as their income rises and cuts out completely at $40,000. The ATO can only check your eligibility for this offset if the spouse details section has their income entered.
Medicare levy reduction for low-income families
Below a separate, lower family income threshold, the base 2% Medicare levy itself can be reduced or exempted for couples and families — a different test to MLS, and one that also depends on declaring a spouse and any dependent children.
Family Tax Benefit and Child Care Subsidy — a Services Australia process
This one sits outside the tax return's spouse section, but the logic carries straight over: if you receive Family Tax Benefit or Child Care Subsidy, Services Australia can only balance your payments for the year once both partners' income is confirmed — either through a lodged tax return or a formal non-lodgment advice. It's a separate process from the ATO return, but it depends on the same underlying fact: what your spouse earned that year.
What doesn't change because you have a spouse
- Your tax bracket and rate — Australia has no joint filing; each return is assessed individually against the Revised Stage 3 rates (16%, 30%, 37%, 45% above the $18,200 tax-free threshold).
- HECS/HELP compulsory repayment — calculated on your own repayment income only, never combined with a spouse's.
- The base Medicare levy rate (2%) — only the surcharge and the low-income reduction are family-tested; the standard levy itself is worked out on your individual income.
Who counts as a spouse for tax purposes, de facto included
The ATO's definition is broader than a marriage certificate. Your spouse includes someone who:
- you are legally married to, or
- you are in a relationship with that is registered under state or territory law, or
- you lived with on a genuine domestic basis in a relationship as a couple — a de facto relationship, regardless of registration.
This applies equally to same-sex and opposite-sex couples: since 1 July 2009, de facto same-sex couples have been treated identically to married couples across every income test and offset. There is no single fixed minimum duration that makes a relationship "count" for tax purposes — the ATO looks at the whole picture, weighing things like shared finances, a common residence, how the relationship is viewed socially, and whether you support each other, rather than ticking off a set number of months. Temporarily living apart — for work, study, illness, or travel — doesn't end the relationship for tax purposes; you still declare each other as spouses. A permanent separation does end it, from the date you actually started living separately and apart, even if a divorce or formal property settlement is finalised later.
A few situations worth flagging directly:
- Your spouse lives overseas or isn't an Australian tax resident. You still need to include their income (converted to AUD) in your own spouse-details section, because it's your family-income test being calculated, not theirs. Their own filing obligations are separate and don't remove your obligation to report their income for your MLS, rebate, and offset eligibility.
- Your relationship started or ended partway through the year. The return asks for the exact date range you had a spouse, and family-income tests are applied pro-rata for the period that applies.
- You genuinely don't know your spouse's exact income. A reasonable, good-faith estimate is accepted — built from their income statement, PAYG payment summary, prior-year notice of assessment, or trust distribution statement if relevant.
What happens if you don't declare a spouse, or get the details wrong
| Situation | Likely consequence |
|---|---|
| You don't declare a spouse the ATO's data matching later identifies (shared address, joint account, matched records) | MLS and/or private health rebate recalculated for the relevant year, creating a tax debt plus the general interest charge on the shortfall |
| You made a reasonable, good-faith estimate of your spouse's income that turns out to be wrong | Generally no penalty for the estimate itself; you may need to lodge an amendment once the correct figure is known |
| You record "no spouse" while in a genuine de facto relationship | Treated as a false or misleading statement — the ATO's test is the facts of the relationship, not what you label it |
| Either partner doesn't lodge a return (or a non-lodgment advice) within the required period, and you receive Family Tax Benefit or Child Care Subsidy | Services Australia can raise a debt for the full amount paid that year, not just the difference |
Records to keep
- Your spouse's income statement, PAYG payment summary, or notice of assessment for the relevant financial year
- Evidence of the date your relationship began or ended, if it changed during the year (lease agreements, joint bank account opening dates, correspondence)
- Evidence of a separation date, if applicable — separate addresses, bank statements, or a formal separation record
- Receipts or fund statements for any spouse super contributions you made
- Your private health insurer's tax statement showing family/couple cover and the exact days held
Quick checklist
- Confirm your relationship status (married, de facto, or separated) as at 30 June, and note any date changes during the year
- Get your spouse's taxable income figure — or a documented, reasonable estimate — before you lodge
- Check whether your combined family income crosses the $202,000 MLS base threshold (plus $1,500 per dependent child after the first)
- Confirm your private health cover is correctly recorded as a family/couple policy on both returns, if applicable
- If your spouse's income is $37,000 or less, check whether a spouse super contribution before 30 June could apply
- If you receive Family Tax Benefit or Child Care Subsidy, make sure both partners lodge — or formally advise Centrelink of income — so payments can be balanced
Working out whether combined income tips a couple into the Medicare Levy Surcharge, a lower private health rebate tier, or an unbalanced family payment is exactly the kind of calculation that goes sideways when two incomes, a mid-year relationship change, or an estimate are involved. A TPB-registered tax agent can check the spouse-details section against your actual family income and lodge the FY2025–26 return for you, with access to the later 15 May 2027 lodgment deadline (instead of 31 October 2026) if you need extra time to track down the figures.
Need Help With Your Tax Return?
Complex situation? a registered tax agent (see the directory) Our partner agents review every detail for accuracy and compliance.
*Disclaimer: This is general information only and does not constitute personal tax advice. Consult a registered tax agent for advice tailored to your specific situation. Always verify against the latest ATO guidelines at ato.gov.au.*
*Disclaimer: general information only — not personal tax advice. Confirm your specific spouse-related thresholds and offset eligibility with a Registered Tax Agent.*