Subdividing your land doesn’t trigger capital gains tax — selling one of the new lots does. That distinction trips up almost everyone who carves off a backyard block. The vacant lot becomes a brand-new CGT asset with its share of your original cost base, and the main residence exemption that protected your home won’t protect the lot you sell separately. In 2026-27 the 50% CGT discount still applies after 12 months of ownership — but one date now dominates every subdivision decision: 1 July 2027, when the discount is legislated to disappear. This guide runs the real rules with dollar figures, the traps the accountant blogs gloss over, and the GST angle most of them ignore.
The short answer
- Subdivision itself is not a CGT event. The ATO splits your parcel into two or more separate CGT assets; nothing is taxed until you sell or transfer one of the new lots (CGT event A1).
- A separately sold lot never gets the main residence exemption. Only land sold with your dwelling is covered. Sell the backyard block on its own and it’s fully taxable, however long it was “part of your home”.
- The cost base is split on a reasonable basis. Original purchase price, stamp duty and legals — plus survey, council and subdivision costs — are apportioned across the new lots, usually by area or market value.
- CGT is timed at the contract date, not settlement. Sign before 30 June 2027 and the old 50% discount still applies (12-month hold); sign on or after 1 July 2027 and the new indexation-plus-30%-floor rules take over.
- Bought to subdivide and sell? That’s ordinary income, not a capital gain. No 50% discount, no capital losses to offset it — and GST may apply on top.
How subdivision triggers CGT
The ATO’s sequence, from its Subdividing land guidance: you subdivide (no tax event), each new lot keeps the original acquisition date — the 12-month discount clock doesn’t restart — and when you sell a lot, CGT event A1 happens. Gain equals sale price minus that lot’s apportioned cost base. Sell one lot this year, keep the other for a decade: they’re taxed completely separately.
The part people under-budget is how wide the cost base is: purchase price plus stamp duty and legals, the surveyor, council DA and application fees, civil works, connections, the valuer’s fee, and the commission and legals when you sell the lot. Every receipt you lose is profit you’re paying tax on.
“Mere realisation” vs a profit-making scheme
The ATO taxes your profit as ordinary income (not a capital gain) if both of these are true: your intention or purpose in subdividing was to make a profit, and it was made in the course of carrying on a business, a business operation or commercial transaction. That second limb catches you even if you aren’t in business — the ATO says so explicitly, including one-off transactions by individuals (TR 92/3).
Two archetypes:
The mere realiser (capital account). You bought the house to live in years ago; the kids moved out, the big block is too much garden, you carve off the back and sell it. You were realising a long-held asset, not running a development. CGT applies, the 50% discount is available after 12 months, and the main residence exemption keeps protecting the lot with the house.
The profit-maker (revenue account). You bought the block with a plan — subdivide into four, sell the lots, bank the margin — and acted like a developer: agents, marketing, maybe a previous project. That profit is ordinary income under section 6-5. No 50% discount however long you held, capital losses can’t reduce it, and it’s taxed at your marginal rates in the year you derive it.
The danger zone is the borderline: a duplex where you keep one and sell the other is often still capital if your intention for your half never changed — but multiple lots plus marketing plus development finance looks like a commercial operation, and the whole tax outcome shifts with it. If there’s doubt, get advice before you lodge the DA, not after the sale contracts are signed.
The main residence exemption trap
The costliest trap for ordinary families sits in section 118-165: the exemption does not apply to land unless the CGT event also happens in relation to the dwelling. The ATO’s line: the exemption applies only to the allotment containing the dwelling — the sale of the second allotment is subject to CGT.
The classic case: house on 1,000m² bought in 2019, lived in throughout, subdivided in 2026 into a 500m² house lot and a 500m² vacant lot, vacant lot sold. The house lot keeps its full exemption for a future sale as your home. The vacant lot gets zero exemption — not half, not pro-rata, zero — even though it was “your backyard” for seven years.
A warning about something you’ll read elsewhere: one accountant blog claims a subdivided lot can get the full exemption if sold “within two years of moving into the retained residence”. That is not how section 118-165 works — don’t plan around it.
The s118-192 reset: a second trap for former rentals
Say you lived in the house, moved out in 2022 and rented it under the six-year rule, then subdivided and sold the back lot in 2026. Section 118-192 deems you to have acquired the property at its market value on the day it was first rented (first rentals after 7:30pm on 20 August 1996) — everything before that day drops out of the cost base, and the reset value is apportioned to the new lots. The six-year absence rule can’t save the back lot: it only exempts a dwelling when the whole property is disposed of together. Get a valuation at the first-rental date — without it, your cost base is guesswork. Our six-year rule guide covers the absence rule in full.
GST on subdivided lot sales
GST is the tax most small subdividers never see coming: it turns on whether you were carrying on an enterprise — not on whether the land was your home.
One-off backyard subdivision by a private owner: usually no GST. Carve off part of your long-held home block and you’re not in an enterprise — CGT is your only concern.
Subdivision as a business or commercial project: GST applies. Each lot sale is a taxable supply. You register for GST and claim credits on development costs — but the buyer of “potential residential land” may have to withhold the GST at settlement and pay it straight to the ATO.
The margin scheme is the relief valve: with a written agreement in the sale contract, GST is 1/11th of the margin (sale price minus apportioned original price) instead of 1/11th of the full price. Quick maths: block bought for $350,000, four lots, one sold for $200,000. Apportioned price: $87,500. Margin: $112,500. GST: $10,227 — versus $18,182 without the scheme, roughly $8,000 saved per lot. The agreement must be in the contract before settlement; miss that clause and there’s no fixing it afterwards.
Step by step: working out your CGT
- Confirm acquisition date and cost base. Purchase price plus stamp duty, legals and capital costs — minus anything already claimed as a deduction.
- Add the subdivision costs. Surveyor, council DA fees, civil works, connections, valuer.
- Apportion on a reasonable basis. By area for equal-value lots; by market value (registered valuer) when they differ.
- Add the sale costs of the lot you sold. Commission, advertising, conveyancing.
- Gain = sale price − apportioned cost base.
- Apply the discount if eligible. Individual or trust, held 12+ months, CGT event before 1 July 2027 → halve the gain.
- Add the net gain to taxable income. No separate CGT rate — it’s taxed at your marginal rate. Try the CGT calculator.
The 1 July 2027 line: the 50% discount survives for CGT events up to 30 June 2027 — the “event” is the contract date, not settlement. From 1 July 2027 the legislated reform replaces it with CPI indexation plus a 30% minimum tax on the real gain; pre-July 2027 gains keep the old treatment. Get a valuation dated near 1 July 2027 either way. Full detail in our CGT reform guide.
Worked example 1: the backyard subdivider
Sarah bought a house on 1,200m² in March 2019 for $800,000 plus $30,000 stamp duty and legals, and lived there throughout. In early 2026 she subdivided into two equal 600m² lots for $35,000, then sold the vacant lot in May 2026 for $650,000. Sale costs: $17,000.
| Cost base item | Amount |
|---|---|
| Original cost base apportioned (50% of $830,000) | $415,000 |
| Share of subdivision costs (50% of $35,000) | $17,500 |
| Sale costs (commission + legal) | $17,000 |
| Total cost base of the sold lot | $449,500 |
| Sale price | $650,000 |
| Capital gain | $200,500 |
| 50% CGT discount (held since 2019; contract May 2026) | ÷ 2 |
| Net gain added to income | $100,250 |
No main residence exemption on the sold lot — sold separately from the dwelling. The retained house lot keeps its full exemption.
Tax effect: on her $95,000 salary, Sarah’s taxable income jumps to $195,250. At 2026-27 rates her income tax rises from $19,020 to about $53,732 — roughly $34,700 extra, plus about $2,000 in extra Medicare levy. That “free money” from the backyard just cost nearly $37,000 in tax. Model your own salary-plus-gain in the income tax calculator.
Worked example 2: a couple splits two lots
Daniel and Aisha bought a house on 1,000m² in 2020 for $1,150,000 (joint tenants, 50/50) with $50,000 purchase costs. In 2026 they subdivide into two equal lots for $40,000 and sell the vacant lot for $720,000 (contract September 2026), with $15,000 sale costs.
Cost base of the sold lot: $600,000 + $20,000 + $15,000 = $635,000. Gain: $85,000, split $42,500 each; each applies the 50% discount → $21,250 each added to taxable income. Nuance: unused capital losses apply against a partner’s $42,500 share before the discount — the other partner can’t use them. If the couple later sells the retained house lot as their main residence, that sale is fully exempt.
Worked example 3: the developer who loses the discount
Sam buys a vacant 2,000m² block in January 2026 for $350,000 to subdivide into four lots and sell. Subdivision and holding costs: $150,000. He sells all four at $200,000 each — $800,000 total.
The plan from day one was subdivision for profit in a commercial-style operation, so the $300,000 profit is ordinary income, not a capital gain. No 50% discount — the full $300,000 is assessable at marginal rates, and no capital losses can offset it. As a discounted capital gain, only $150,000 would have been taxable.
GST bites too if Sam is registered as an enterprise: with the margin scheme in the contracts, GST per lot is ($200,000 − $87,500) ÷ 11 = $10,227 (~$40,909 total) versus $18,182 per lot without it. One contract clause saves over $30,000 — and the buyers withhold the GST at settlement for the ATO.
Common mistakes
1. Assuming the backyard lot is exempt because the home is. The exemption covers the dwelling and land sold with it — never a separately titled lot.
2. Timing the gain to settlement. CGT event A1 is the contract date. A 28 June 2027 contract with August settlement keeps the old discount rules; a 3 July 2027 contract doesn’t.
3. Leaving subdivision costs out of the cost base. Survey, DA fees, civil works, connections, valuer — all shrink the gain.
4. Splitting 50/50 by area when the lots differ in value. “Reasonable basis” is the test — a valuer’s report at subdivision date is cheap insurance.
5. Claiming the 50% discount on a development profit. Recharacterised as a profit-making scheme, the discount vanishes — and capital losses can’t touch the profit.
6. Forgetting GST entirely. Private one-off? Fine. Enterprise-like? GST, margin scheme and buyer withholding apply — budget for them first.
7. No valuation at the key dates. Subdivision date, first-rental date, 1 July 2027. Retrospective valuations are harder and dearer.
Tips before you subdivide
- Get tax advice before the DA, not after the sale. Capital vs revenue turns on your intention and conduct.
- Commission a registered valuation at subdivision. It locks in an apportionment the ATO will accept.
- Keep every invoice. Council, surveyor, solicitor, works, connections, agent — if it’s in the cost base, you need proof.
- Mind the contract date around 30 June 2027. Days can decide whether the 50% discount applies to a six-figure gain. Our property CGT guide covers the discount rules.
- Put the margin-scheme clause in the contract. If GST applies, the written buyer agreement must predate settlement.
- Plan the retained lot too. Today’s cost-base split sets up the gain on the lot you keep. See our main residence exemption guide.
FAQ
Does subdividing my land trigger CGT by itself?
No. One asset becomes two or more, each keeping the original acquisition date. CGT bites when you sell or transfer a new lot (CGT event A1).
Is the subdivided backyard covered by my main residence exemption?
No, if sold separately from your home: s118-165 limits the exemption to land sold with the dwelling, so the vacant lot’s gain is fully taxable.
Can I get the 50% CGT discount on a subdivided lot?
Yes — individual or trust, 12+ months held, capital account, CGT event before 1 July 2027. Profit-making schemes taxed as ordinary income get no discount.
Do I pay GST when I sell a subdivided lot?
It turns on the enterprise test, not the land. A one-off subdivision of your long-held home block is usually not an enterprise — no GST. A commercial project is — GST applies, the margin scheme can cut it to 1/11th of the margin, and the buyer may withhold GST at settlement.
How do I split the cost base between the new lots?
On any “reasonable basis”: by area for equal-value lots, by market value (registered valuer) when they differ — folding in purchase costs, stamp duty, subdivision costs and sale costs.
What if I bought the land before 20 September 1985 (pre-CGT)?
The lots inherit pre-CGT status, so gains are generally exempt today. Caveats: big improvements can be separate post-CGT assets, and the 2027 reform brings post-2027 growth on pre-CGT assets into the CGT net — get a valuation near 1 July 2027.
The bottom line
Subdivision rewards the prepared and punishes the casual. The families who come unstuck assumed the backyard lot was exempt, left subdivision costs out of the cost base, or signed the sale contract without knowing which side of 1 July 2027 they were on. Get classification right, get a valuer’s apportionment, keep every invoice, and check GST before the DA goes in.
Checked against the ATO’s Subdividing land guidance and the CGT guide’s real estate section, plus the Treasury Laws Amendment (Tax Reform No. 1) Act 2026. Anything beyond a simple backyard carve-off deserves a registered tax agent before you sell.
