A student started mining Bitcoin in high school, purely for fun, squeezing in a session here and there whenever gaming wasn’t taking up his time. He never chased profit with it. Across the years, the most his little stash of buys, sells, and trades was ever worth probably averaged out at around $250, and he never bothered saving any of it properly. By 2018, the novelty had worn off. It felt more like gambling than anything he actually enjoyed, so he withdrew whatever small amounts each exchange would let him cash out, skipping the rest because the withdrawal fees would have eaten more than the balance was worth.
Then, a few years later, Elon Musk’s on-again-off-again crypto antics reminded him he still had some coins floating around somewhere. When he went looking, he found close to $1,000 in Bitcoin, scattered across a handful of wallets he’d forgotten existed. He withdrew it all in 2024. Not long after, a letter from the Australian Taxation Office turned up, titled “Did you dispose of your crypto assets?” The ATO said it had received information that he’d sold crypto, and that he needed to pay capital gains tax on it. He had until December to report it voluntarily, or risk a penalty if an audit later found he hadn’t.
He’d never had anywhere near $1,000 in crypto before. He never treated it as an investment. He mined it, mostly forgot about it, and cashed it out on a whim. Was this really something the ATO cared about? And could it possibly count as a personal use asset, the one exemption he’d heard might let small amounts like his slip through tax-free?
Is Forgotten Crypto Still Taxable When You Finally Sell It?
Yes. When you sell, swap, spend or convert crypto to cash, the transaction can trigger a CGT event. In this case, the Bitcoin was mined years earlier and eventually converted to cash in 2024, so the disposal needs to be considered for tax purposes.
The tax treatment of the original mining depends on whether it was a business or a hobby. Someone mining at a commercial scale and carrying on a business generally has to treat mined coins as ordinary income when received, with that value becoming the cost base for a later disposal.
How the original mining gets taxed depends entirely on whether it was run as a business or done casually. Someone mining at a genuine business or professional level has to treat the coins as ordinary income at market value the moment they’re received, and that value becomes the cost base for whatever happens next. “If you’re mining at a genuine business or professional level, that income is treated as business income,” says Ankush Kumar, Crypto Tax and Accounting Analyst at KoinX.
Casual, hobby-level mining works differently: nothing gets taxed at the point of receipt. Instead, the coins are treated as capital assets with a cost base that’s often low or nil, so when they’re eventually sold, most of the proceeds can end up counted as a capital gain. That’s the trap specific to hobby mining: the tax bill doesn’t show up when the coins are mined, it shows up all at once at the point of sale, often larger than expected precisely because there’s little or no cost base to subtract.
Is This Actually a Personal Use Asset?
Crypto may qualify where it was acquired specifically to buy something for personal use or consumption and was used that way within a relatively short period. Simply holding crypto and later selling it does not generally meet that test.
That distinction matters here because the Bitcoin was mined, held for years and eventually converted to cash. It was never acquired and used to purchase a personal item. There is also a specific restriction for mined crypto: the personal use asset exemption does not apply to gains from the disposal of mined coins.
So even though the amount was small and the Bitcoin was held casually, the personal use asset exemption does not remove the tax consequence of the eventual disposal.
Decoding the Numbers
The Reddit post didn’t include exact figures for each wallet, so here’s a worked example built the same way, with every number checked.
Someone mined small, irregular amounts of Bitcoin on a home computer between 2013 and 2016, purely as a hobby, never running it as a business and never claiming any deductions. By 2024, the fragments sitting across three old wallets add up to $980 when finally converted to cash. Because this was hobby mining, the coins weren’t counted as income when they were mined, and no costs were ever deducted against them, so the entire $980 counts as capital proceeds with next to nothing to subtract as a cost base. That makes the capital gain effectively the full $980.
Because every fragment had been sitting untouched for well over 12 months, most of it for closer to a decade, the 50% discount applies to the whole amount. Taxable capital gain: $980 × 50% = $490, added to assessable income for the 2024-25 financial year.
Look at where the actual number lands. Once the 50% discount is applied, this is a small addition to someone’s tax bill, not a life-changing one. The real risk was never the size of the gain. It was the possibility of not reporting it at all.
The Two Ways Mining Ends Up Taxed
Situation | How the ATO taxes it | When it’s counted | What it means for the disposal |
Casual, hobby-level mining | Not counted as income when received | No tax event at the time of mining | Almost the entire sale amount later counts as a capital gain, since there’s little to no cost base |
Business-level mining | Counted as ordinary income at market value | The day the coins are mined | That value becomes the cost base for any later sale |
Selling or converting mined crypto to cash | Capital gains tax | The day of the sale | Gain = proceeds minus cost base (often close to nil for hobby miners) |
Holding crypto for more than 12 months before selling | 50% discount applies to the gain | Only at the point of sale | Halves the taxable portion |
Using crypto to directly buy something personal, under $10,000, soon after acquiring it | May qualify as a personal use asset | Rarely applies to mined crypto | Gain may be disregarded, but this exemption doesn’t apply to mining disposals at all
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How the ATO Spots the 2024 Cash-Out
The ATO’s data-matching program pulls information directly from Australian-licensed exchanges, and it can trace wallet addresses and bank accounts back to real people, going back as far as 2014. For someone who mined coins years ago and left them scattered across old wallets, the ATO almost certainly couldn’t see any of that activity while the coins sat untouched. What it could see was the moment those old, disconnected wallets got consolidated and converted to cash on an Australian exchange in 2024. That single event, the cash-out, is what an exchange reports directly, and it’s very likely what triggered the letter.
Kumar sees this pattern constantly in how tax authorities actually build their picture of someone’s crypto activity. “Tax authorities generally only find out about crypto activity because centralised exchanges report it,” he says. “Decentralised exchanges don’t report anything to any tax authority, anywhere. So the moment you trade or cash out on a centralised exchange, that exchange is reporting your transaction data to the tax authority in whatever country you’re in. If what you’ve declared as income or gains doesn’t match what the exchange reported, that mismatch is usually what triggers a notice.” That’s the exact shape of this case: years of quiet mining that never crossed any exchange’s radar, followed by one visible cash-out that did.
How KoinX Helps Untangle Old, Scattered Wallets
This is precisely the kind of situation KoinX is built to sort out, old crypto spread across wallets and exchanges someone barely remembers using, with no clean record of what came from mining, what came from a trade, and what it was all worth at the time. Here’s what that actually looks like.
- Connect every wallet and exchange, even the ones you’ve forgotten about: You start with a free account, then link each wallet or exchange the coins might be sitting in or might have passed through. KoinX supports hundreds of exchanges and wallets directly, and file uploads cover the rest.
- Let KoinX pull in and reconstruct the full history. Once everything is connected, KoinX rebuilds the timeline automatically, matching up mining rewards, transfers between wallets, and the eventual sale, rather than leaving you to piece together years of scattered activity by hand.
- Generate the report. For the worked example above, that would mean a report showing the $980 disposal, the 50% discount correctly applied, and a $490 taxable capital gain flagged for 2024-25, all backed by the actual transaction history rather than a rough guess. That’s the report you can hand to a tax agent or use to respond to a letter like this one directly.
Responding to the Letter
Kumar is direct about this part. “Responding to a notice is mandatory in every case,” he says. “If a tax authority sends you a message saying there’s a mismatch between what you’ve declared and what they can see, whether that’s from a centralised exchange or anywhere else, you have to respond to it. Say someone cashes out five thousand dollars on a centralised exchange. The tax authority doesn’t automatically know why. It could be salary, it could be consultancy income, it could be a straightforward trade. You have to tell your side of the story.” In this case, that means confirming the coins came from years of casual mining, working out the actual capital gain, and reporting it before the December deadline in the letter.
That deadline matters more than it might seem. The ATO’s own guidance on voluntary corrections explains that a base penalty is generally reduced by 80% if you disclose a shortfall before the ATO formally notifies you it’s examining your affairs, or reduced to nil entirely if the shortfall is under $1,000, according to the ATO’s page on penalties for voluntary corrections. A letter like this one, offering a chance to report before December, sits squarely inside that window. Responding to it properly isn’t just the compliant thing to do. It’s the version of this that costs the least.
What Happens If You Miss the December Deadline?
Missing the deadline doesn’t automatically mean a heavy penalty, but it can mean losing the more favourable treatment available through voluntary disclosure.
If the ATO later finds an undeclared gain, the consequences can include:
- Penalties: The base penalty can be 25% of the tax shortfall for failing to take reasonable care, 50% for recklessness, or 75% for intentional disregard of the rules.
- Interest: Any unpaid tax can also attract interest until it is paid.
- Voluntary disclosure: Disclosing a shortfall before the ATO formally notifies you that it is examining your affairs can reduce the base penalty by 80%. Where the shortfall is below $1,000, the penalty may be reduced to nil under the ATO’s voluntary correction rules.
- Penalty units: Separate federal-law penalties are calculated using penalty units, which are currently $364 as of July 2026.
The key takeaway is that responding to the ATO before the matter escalates can put the taxpayer in a more favourable position than waiting for an audit to uncover the undeclared amount.
The Redditor who posted his ATO letter will likely end up owing a modest amount once the numbers are worked through properly, nowhere near enough to justify the anxiety the letter clearly caused him. What actually mattered was never the size of the balance. It was that a decade-old hobby, forgotten and rediscovered by accident, still counted as an asset the moment he decided to cash it in.
