Capital gains tax (CGT) is one of the most significant tax obligations that property owners in Australia face — and it's also one of the most misunderstood. Many people assume CGT only applies when they sell an investment property at a profit. In reality, CGT events are triggered by a much wider range of circumstances, and the way your property was acquired, used, and valued along the way can have a major impact on how much tax you pay.
At the centre of many CGT calculations is a formal property valuation. Not a bank estimate, not an online tool, not a real estate agent's opinion — a formal, documented assessment by a registered, independent valuer. The ATO is explicit about this, and the consequences of getting it wrong can be costly.
This guide explains how CGT applies to property in NSW, when a formal valuation is required, what the ATO expects from that valuation, and how to protect your tax position with the right documentation.
How CGT Works for Property in Australia
Capital gains tax is a tax on the profit (gain) you make when you dispose of an asset. For property, disposal most commonly means a sale, but it can also include gifting the property, transferring it on relationship breakdown, or in some cases, changing how the property is used. The gain is calculated as the difference between the capital proceeds (what you received) and the cost base (what you paid for it, plus allowable costs).
CGT is not a separate tax — it is included in your assessable income for the year in which the CGT event occurred, and taxed at your marginal rate. However, if you have held the property for more than twelve months, you may be entitled to a 50% CGT discount — meaning only half the gain is included in your assessable income.
The CGT regime applies to assets acquired on or after 20 September 1985. Assets acquired before this date are referred to as pre-CGT assets and are generally exempt from CGT. However, even with pre-CGT assets, a formal valuation may be needed — because the cost base of a pre-CGT asset is its market value as at 20 September 1985, not what you originally paid for it.
Your principal place of residence (your home) is generally exempt from CGT for the period you lived in it. But if you rented the property out for a period, moved away, used it for income-producing purposes, or have multiple properties, the exemption may be partial or unavailable, and a valuation may be needed to calculate the taxable portion of any gain.
When Is a Property Valuation Required for CGT Purposes?
Pre-CGT Assets: Valuation as at 20 September 1985
If you own (or have sold) a property that was acquired before 20 September 1985, the cost base for CGT purposes is the market value of the property on that date — not the original purchase price. This is because CGT did not exist when the property was acquired, and it would be inequitable to tax gains that accrued before the tax existed.
To calculate the CGT-free component correctly, you need a formal retrospective valuation establishing what the property was worth on 20 September 1985. This is a specialised assignment requiring access to historical sales data and expertise in historical market conditions. Not all valuers undertake this type of work.
The ATO can and does challenge CGT calculations based on unsupported or poorly documented cost bases. A formal retrospective valuation, prepared by a qualified independent valuer and retained on file, is the best protection against an adverse ATO determination.
If you inherited a pre-CGT property from an estate, or if a pre-CGT property passed to you on relationship breakdown, the CGT implications require careful analysis. Your accountant should advise on the specific rules that apply to your situation.
Changing Use: Residential to Investment Property
One of the most common situations requiring a CGT valuation is converting your principal residence to a rental property — or, less commonly, moving into a property that was previously rented. When a property changes from a private residence to an income-producing asset, a CGT event may occur, and the market value at the time of the change in use becomes the new cost base (or part of it).
The ATO's six-year rule allows you to treat a property as your main residence for up to six years while renting it out, provided you don't nominate another property as your main residence during that period. However, once the property has been rented for more than six years, you will have a partial CGT liability on sale, calculated by reference to the proportion of time the property was used as a residence versus an income-producing asset.
In these situations, establishing the market value of the property at the date it first became an income-producing asset — or at the date you moved back in — is critical to calculating the taxable gain correctly. Without a formal valuation at that date, the cost base calculation is unsupported and vulnerable to ATO challenge.
Many property owners who converted their home to a rental property years ago have not obtained a valuation at the time of the change. If you are in this situation and are planning to sell, speak with your accountant urgently — it may still be possible to commission a retrospective valuation for the relevant date, though it becomes harder the further in the past the date is.
Inherited Property and Deceased Estates
When you inherit property from a deceased estate, the CGT rules that apply depend on when the deceased acquired the property and whether it was their main residence. For properties acquired after 19 September 1985, you generally inherit the property at the deceased's cost base — meaning you carry over their original purchase price as your starting point.
However, for properties that were the deceased's main residence at the date of death, and which you sell within two years of the date of death, you may be fully exempt from CGT. If you sell after two years, or if the property was not the deceased's main residence, a valuation at the date of death establishes the market value that becomes your cost base.
Understanding which rules apply requires careful analysis of the deceased's ownership history, how they used the property, and when they acquired it. Your accountant or solicitor will advise, but in most cases where property passes through an estate, a formal valuation at the date of death is required — both to calculate the estate's value for probate and to establish the cost base for the beneficiary's future CGT calculations.
Failing to obtain a date-of-death valuation at the time of estate administration creates a significant problem when the property is eventually sold. The later you commission the retrospective valuation, the harder it becomes to access reliable historical evidence.
Gifts and Non-Arm's-Length Transfers
If you give property to someone — a family member, a related entity, or a trust — without receiving full market value in return, a CGT event is triggered. The capital proceeds are deemed to be the market value of the property at the time of the gift, regardless of what (if anything) was actually received.
This means that gifting a property to a family member at no cost or at a reduced price does not avoid CGT — it crystallises it, with the gain calculated on the full market value at the date of the gift. A formal valuation at the date of the transfer establishes the proceeds figure for CGT purposes and provides the documentation needed to support the tax return.
Transfers on family law settlement — where property passes between spouses as part of a property settlement — are generally CGT-exempt, provided the transfer occurs in compliance with a court order or formal financial agreement. However, the rules are complex, and professional advice is essential before assuming an exemption applies.
For any non-arm's-length transaction involving property, a formal valuation at the time of the transfer is essential documentation. The ATO can and does review these transactions, and an unsupported market value claim is a significant audit risk.
What the ATO Expects from a CGT Valuation
The ATO's guidance on CGT valuations is clear: valuations must be undertaken by a suitably qualified independent professional. The valuation must be based on objective, verifiable evidence — not an automated estimate, an agent's appraisal, or the taxpayer's own opinion. And it must be documented in a way that allows the ATO to assess the methodology and evidence if the return is reviewed.
For CGT valuations, the ATO expects the report to state the property address and description; the relevant valuation date (which may be a retrospective date); the methodology used; the comparable sales evidence relied upon; and the assessed market value. The report must be signed by the registered valuer and include their licence number and qualifications.
The ATO may substitute their own valuation if they consider the taxpayer's valuation to be unsupported or inaccurate. In that case, the taxpayer has the burden of proving that their valuation is correct — and a formal, well-documented report from a qualified valuer is the most effective tool for doing so.
Retaining the valuation report on file — even if the ATO does not request it at the time of lodgement — is essential. CGT returns can be reviewed for up to four years after lodgement (longer in cases of fraud or evasion). The valuation report is the audit trail that protects the taxpayer if a review occurs years later.
The Cost of Getting It Wrong
Submitting a CGT calculation based on an unsupported valuation — or worse, no valuation at all — creates serious tax and financial risks. If the ATO substitutes a lower cost base, the taxable gain increases, and the taxpayer may owe additional tax plus interest and potentially penalties.
Even if the ATO does not challenge the return initially, a later review can result in an amended assessment and significant catch-up tax liability. The interest component alone on underpaid tax can be substantial if the CGT event occurred years before the review.
By contrast, the cost of a formal CGT valuation at the time of the event is modest relative to the amounts at stake. A residential valuation in metropolitan Sydney is a one-off professional fee. The tax saving from a correctly documented cost base — or the protection against an incorrect ATO determination — routinely exceeds the valuation fee many times over.
CGT is an area where the investment in professional advice — accountant, valuer, and solicitor where needed — pays dividends. Trying to manage a complex CGT situation without proper documentation is a false economy.
Frequently Asked Questions
Do I need a valuation every time I sell a property?
Not necessarily. If the property was your main residence for the entire period you owned it and you are claiming the full main residence exemption, no CGT applies and no valuation is needed. If the property has always been an investment and you have clear records of your original purchase price and eligible cost base additions, you may not need a formal valuation — though your accountant should confirm this. Valuations are specifically required when establishing a market value cost base at a particular date, such as when a property changes use, is inherited, or was acquired before September 1985.
What if I didn't get a valuation at the time of the CGT event?
You may still be able to commission a retrospective valuation for the relevant past date. The further in the past the date is, the more difficult and expensive the retrospective valuation becomes, as historical evidence becomes scarcer. However, a well-documented retrospective valuation from a qualified valuer is far better than no valuation at all. If you are in this situation, speak with your accountant as a first step — they will advise whether a retrospective valuation is needed and what documentation you should gather.
Can I use an online estimate or a real estate agent's appraisal for CGT purposes?
No. The ATO requires that valuations for CGT purposes be prepared by a suitably qualified independent professional. An automated online estimate or a real estate agent's appraisal does not meet this standard. Using an unsupported figure as a cost base in a CGT calculation creates an audit risk, and if the ATO challenges it, the burden of proof is on the taxpayer to establish the correct value with proper evidence.
Does the 50% CGT discount apply to all property?
The 50% CGT discount applies to property held by Australian resident individuals and trusts for more than twelve months. It does not apply to companies. For SMSFs, a one-third discount applies (reducing the effective rate to two-thirds of the gain) for assets held more than twelve months. The discount applies to the net capital gain after applying any capital losses. Your accountant will calculate the correct discount and advise on any special rules that apply to your situation.
What records do I need to keep for CGT purposes?
You should keep records of the original purchase price and all purchase costs (stamp duty, legal fees, agent's fees); any capital improvements made during ownership (receipts and invoices); the valuation report if a market value cost base was established at any point; records of any periods of private use versus income-producing use; and sale records including the contract of sale. The ATO can require records going back many years for CGT purposes, so secure, long-term storage of these documents is important.
Is there CGT on the sale of my main residence?
In most cases, no — the main residence exemption removes CGT on the sale of your home, provided you lived in it for the entire ownership period, it was never used to produce income, and it is on land of 2 hectares or less. However, the exemption is partial if you rented the property out at any point, used part of it for business purposes, or have multiple properties. If your situation is anything other than straightforward, your accountant should assess your CGT position before you sell.
