Published: 1 April 2026

How to Calculate Capital Gains on Shares: A Complete Guide for Australian Investors

Sold some shares and wondering how much tax you'll owe? Whether you've dabbled in the stock market for years or recently made your first trade, understanding how to calculate capital gains on shares is essential for every Australian investor. Unlike property, shares are easy to buy and sell with a few clicks, which means you might trigger a capital gains tax (CGT) event more often than you realise.

The good news is that calculating capital gains on shares is straightforward once you understand the basics. In this comprehensive guide, we'll walk you through everything you need to know about calculating CGT on shares for the 2025-26 financial year. From determining your cost base to claiming the valuable 50% discount, you'll learn how to accurately report your share trading activities and potentially reduce your tax bill.

Understanding Capital Gains Tax on Shares

Capital Gains Tax on shares works the same way as CGT on other investments like property. When you sell shares for more than you paid for them, the profit is considered a capital gain and must be declared in your tax return. This gain is added to your other taxable income — such as your salary, take-home pay, and investment income — and taxed at your marginal rate.

A CGT event occurs each time you sell or dispose of shares. This includes selling through a broker, transferring shares to someone else, or even receiving proceeds from a company takeover or merger. Even if you reinvest your dividends through a dividend reinvestment plan (DRP), those additional shares have a cost base that needs to be tracked for future CGT calculations. Many investors are surprised to learn that using a DRP doesn't eliminate CGT — it simply defers it until you eventually sell those shares.

It's also worth noting that not all share transactions trigger CGT. If you sell shares at a loss, that creates a capital loss which can be used to offset other capital gains. Additionally, certain shares like those held in retirement phase superannuation accounts may have different tax treatment. Understanding these nuances helps you plan your investment strategy while staying compliant with the Australian Taxation Office (ATO).

How to Calculate Your Capital Gain on Shares

The basic formula for calculating capital gains on shares is simple: subtract your cost base from your capital proceeds. Your capital proceeds are the amount you receive from selling the shares (typically the sale price minus brokerage fees). Your cost base includes the purchase price plus any associated costs like brokerage fees, stamp duty (if applicable), and certain other acquisition expenses.

Let's look at a practical example. Imagine you bought 1,000 shares in a company at $25 per share, paying $20 in brokerage. Your cost base would be $25,020 ($25,000 purchase price + $20 brokerage). Two years later, you sell those shares for $40 per share, paying another $30 in brokerage. Your capital proceeds are $39,970 ($40,000 sale price - $30 brokerage). Your gross capital gain is $14,950 ($39,970 - $25,020).

If you've held the shares for more than 12 months, you can apply the 50% CGT discount, reducing your taxable gain to $7,475. This discounted amount is then added to your other income for the year. If you're in the 30% tax bracket, for example, your CGT liability on this transaction would be approximately $2,243 — a significant saving compared to the $4,485 you'd pay without the discount.

The 50% CGT Discount for Shares

One of the most valuable concessions for Australian share investors is the 50% CGT discount for assets held longer than 12 months. This discount is available to individual taxpayers and trusts, but not to companies. To qualify, you must have owned the shares for at least 12 months before the CGT event (the sale date), and you must be an Australian resident for tax purposes.

The 12-month period is calculated from the date you acquired the shares to the date you disposed of them. For shares purchased on different dates, each parcel is treated separately. This is particularly important if you've been accumulating shares in the same company over time through multiple purchases or a dividend reinvestment plan. When you sell, you can choose which parcels to sell to optimise your tax outcome — a strategy known as "specific identification."

The CGT discount can result in substantial tax savings, especially for higher-income earners. Consider someone in the 37% tax bracket who makes a $50,000 capital gain on shares. Without the discount, they'd pay $18,500 in tax. With the 50% discount, only $25,000 is added to their taxable income, resulting in a tax bill of $9,250 — a saving of $9,250. This is why long-term investing is often more tax-effective than frequent trading, and why understanding your income tax bracket is crucial when planning share sales.

Record Keeping for Share Investors

Accurate record-keeping is absolutely essential for calculating capital gains on shares. The ATO requires you to keep records of all share transactions for at least five years after the relevant tax return is lodged. For shares you still hold, you need to keep records until you sell them and then for another five years.

For each share purchase, you should record: the date of purchase, the number of shares acquired, the purchase price per share, total cost including brokerage, and any other associated costs. For dividend reinvestment plans, you need to record the date shares were acquired, the number of shares, and the amount of dividends reinvested (this becomes your cost base for those shares). For sales, record the date of sale, number of shares sold, sale price per share, and brokerage fees paid.

Many investors use portfolio tracking software or spreadsheets to maintain these records. Your broker typically provides contract notes for each trade, which contain most of the information you need. However, if you've changed brokers over the years or if a company has undergone corporate actions like share splits, consolidations, or takeovers, your records may need additional attention. Good record-keeping not only ensures accurate CGT calculations but can also help you identify opportunities to harvest capital losses or time your sales strategically.

Handling Capital Losses on Shares

Not every share investment results in a profit. When you sell shares for less than you paid, you incur a capital loss. While nobody wants to lose money, capital losses aren't entirely without benefit — they can be used to offset capital gains, reducing your overall CGT liability.

The process works as follows: you add up all your capital gains for the year, then subtract any capital losses. If the losses exceed the gains, you have a net capital loss that can be carried forward to future years. Importantly, you cannot use capital losses to offset your regular income like salary or wages — they can only reduce capital gains. However, capital losses can be carried forward indefinitely until you have capital gains to absorb them.

When applying losses, you must offset them against gains before applying the 50% discount. For example, if you have a $20,000 capital gain (from shares held over 12 months) and a $5,000 capital loss, you subtract the loss first to get $15,000, then apply the 50% discount to arrive at a taxable gain of $7,500. You cannot apply the discount first and then subtract the loss. Some investors deliberately realise capital losses near year-end to offset gains — a strategy called "tax loss harvesting" — though you should never let tax considerations override good investment decisions.

Special Situations and Considerations

Share investments can involve complex situations that affect your CGT calculations. Corporate actions like share splits, consolidations, rights issues, and takeovers can all impact your cost base and the number of shares you hold. When these occur, the company typically provides guidance on how to adjust your records for tax purposes.

Dividend reinvestment plans require special attention. Each time you reinvest dividends, you're essentially buying new shares, and those shares have their own acquisition date and cost base. This means a single parcel of original shares can spawn numerous smaller parcels over time, each with different purchase dates and prices. When you eventually sell, you'll need to account for each parcel separately or use an averaging method if you meet certain conditions.

Your overall tax position is also affected by how capital gains interact with other elements of the tax system. Capital gains can push you into a higher income tax bracket, affect your liability for the Medicare levy, and impact HECS-HELP repayment obligations. Additionally, if you're making salary sacrifice contributions to superannuation, these can help reduce your taxable income in years when you realise significant capital gains. Understanding these interactions helps you see the complete picture of your tax obligations.

Summary and Key Takeaways

Calculating capital gains on shares doesn't have to be complicated. The key steps are: determine your cost base (purchase price plus brokerage and other costs), calculate your capital proceeds (sale price minus brokerage), subtract the cost base from the proceeds to find your gross gain, and apply the 50% discount if you've held the shares for more than 12 months. The resulting net capital gain is added to your other income and taxed at your marginal rate.

For the 2025-26 financial year, remember that the 50% CGT discount remains one of the most valuable concessions for Australian share investors. Good record-keeping is essential — maintain detailed records of every purchase, sale, and dividend reinvestment. If you have capital losses, use them strategically to offset gains. And consider how share sales fit into your overall tax position, including their impact on your take-home pay and other tax obligations.

While this guide covers the fundamentals, share investing can involve complex situations. If you're dealing with large portfolios, frequent trading, corporate actions, or inherited shares, consulting a registered tax agent or accountant is often worthwhile. The cost of professional advice is usually far less than the potential cost of errors or missed opportunities in your CGT calculations.