Share matching
Ireland's four-week rule for shares, and what it actually does
Section 581 of the Taxes Consolidation Act 1997 contains two separate four-week rules for shares. They are routinely described as one rule, and the version that circulates most widely — that a loss is simply cancelled — is not what either of them says.
Last reviewed 10 August 20267 min readIreland
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There are two four-week rules
Both live in the same section, both use a four-week window, and they do entirely different jobs. One changes which shares are treated as sold. The other changes what a loss can be used against.
| Rule one | Rule two | |
|---|---|---|
| Trigger | You sell shares within four weeks after buying shares of the same class | You dispose of shares at a loss and reacquire the same shares within four weeks |
| Effect | The sale is matched against the recent purchase rather than the oldest holding — the reverse of the ordinary FIFO order | The loss is ring-fenced: it can only be set against a gain on a later disposal of the reacquired shares |
| Applies to | Gains and losses alike — it is a matching rule, not a relief restriction | Losses only |
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A single sequence of trades can engage both, and they interact: rule one decides what the gain or loss on the disposal actually is, and rule two then decides what can be done with it if it is a loss.
Rule one: selling within four weeks of buying
The ordinary Irish identification rule is first in, first out — the oldest shares are treated as sold first. Section 581 carves an exception out of it. Where a sale takes place within four weeks of a purchase, Revenue treats the shares sold as being those purchased in the four weeks before the sale.
Where the shares bought in that window are fewer than the number sold, the excess reverts to the ordinary FIFO order and is matched against the oldest holding as usual.
Rule one, in numbers
A holding built up over two purchases, then a partial sale eighteen days after the second.
- 10 January 2026 — bought 100 unitsat €10.00
- €1,000.00
- 2 March 2026 — bought 100 unitsat €14.00
- €1,400.00
- 20 March 2026 — sold 100 unitsat €15.00
- €1,500.00
- Matched cost under the four-week rulethe 2 March purchase
- €1,400.00
- Chargeable gain
- €100.00
Under plain FIFO the sale would have been matched against the January lot at €1,000.00, producing a €500.00 gain. The four-week rule is what makes the difference, and it applies whether the outcome is higher or lower.
Rule two: buying back within four weeks of a loss
The second rule is the anti-avoidance one, and it is the rule people mean when they say “bed and breakfasting”. Revenue states it directly: where shares are repurchased within four weeks of a sale, any loss arising on the sale will only offset a gain made on a subsequent disposal of the repurchased shares.
The loss is not deleted. It is ring-fenced — locked to the specific reacquired holding, and unavailable against anything else, in that year or any later one, until that holding is itself disposed of at a gain.
Rule two, in numbers
A holding sold at a loss and bought back thirteen days later, then sold again in September.
- 5 February 2026 — sold 200 unitscost €6,000.00, proceeds €4,000.00
- −€2,000.00
- 18 February 2026 — reacquired 200 unitswithin four weeks
- €4,200.00
- 10 September 2026 — sold those 200 unitsproceeds €6,600.00
- €2,400.00
- Ring-fenced loss now usable
- −€2,000.00
- Net gain for the year on this holding
- €400.00
Had the investor also made a €5,000.00 gain on an unrelated share in 2026, the €2,000.00 loss could not have been set against it — the ring-fence holds it to the reacquired units until they are disposed of.
The practical consequence is a timing one. The loss survives, but it becomes dependent on a future event — the disposal of the reacquired holding at a gain — rather than being available against the year's gains generally.
The misconception worth clearing up
The version of this rule that circulates most widely is that if you buy back within four weeks, “the original cost carries over and no loss can be claimed”. That is not what section 581 does, and the difference matters.
| Frequently said | What the rule actually does |
|---|---|
| The loss is disallowed | The loss is allowable. It is restricted as to what it can be set against. |
| The old cost base transfers to the new shares | The reacquired shares have their own cost — what you paid for them. The restriction attaches to the loss, not to the cost base. |
| It only catches deliberate tax planning | Both rules operate on dates alone. A rebalance, a reversed order or a change of mind engages them exactly as readily as anything else. |
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What counts as the same shares
Both rules operate on shares or securities of the same class in the same company, held in the same capacity. Some boundaries follow from that:
- Ordinary shares and a different class of share in the same company are different assets.
- Two different companies are two different assets, however closely their prices move together.
- Two different funds tracking the same index are different assets — though funds raise a separate question, below.
- “In the same capacity” matters: a holding you own personally and one you hold as a trustee are not the same person for these purposes.
Where a specific fact pattern sits close to one of these lines, it is the sort of question worth putting to Revenue or a qualified professional rather than resolving from a general guide.
Counting the four weeks
Four weeks is twenty-eight days. It is not “a month”, and the difference is real in a thirty-one-day month: a repurchase on day thirty is outside the window; one on day twenty-eight is not.
| Sold at a loss | Reacquired | Days | Inside the window |
|---|---|---|---|
| 1 February | 25 February | 24 | Yes |
| 1 February | 1 March | 28 | Yes |
| 1 February | 5 March | 32 | No |
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Illustrative day counts. Where a date falls near the boundary, the exact reckoning of the period is a point to confirm rather than estimate.
Trade dates are what count, and they are what your broker's contract note records. Settlement dates are not the relevant dates for identifying a disposal.
Funds and ETFs
Section 581 sits inside the Capital Gains Tax code, and it operates on allowable losses. Irish and EU-domiciled funds are not in that code: they fall under the investment undertaking and offshore fund regimes — 41% to 2025, 38% from 2026 — where a loss on disposal is not an allowable capital loss in the first place, and cannot be set against gains elsewhere at all.
Where there is no allowable loss, the loss restriction in rule two has nothing to bite on. That does not make the fund position more favourable — the loss was already unusable, for a different and broader reason. The ETF tax guide sets out how that regime treats losses.
Why the rule exists
Both parts of section 581 are anti-avoidance provisions, aimed at disposals and reacquisitions arranged over a short interval to manufacture a tax result while leaving the underlying economic position unchanged. Revenue describes the section as designed to limit the manipulation of capital losses by disposals and reacquisitions of shares or securities within a short time.
That framing explains why the rules are automatic and unelectable. They are drafted to apply on dates rather than on intention, which means they catch trades made for entirely ordinary reasons — rebalancing, reversing a mistake, or simply changing your mind — exactly as readily as anything else.
Where this shows up in a calculation
A FIFO engine that ignores section 581 will produce the wrong matched cost for any disposal made within four weeks of a purchase, and will treat a ring-fenced loss as freely available. Both errors move the final figure. If your own working shows a disposal close behind a purchase of the same holding, that is the point at which the general FIFO rule stops being the whole answer.
Sources
- Revenue — Selling or disposing of shares (FIFO, four-week rule, four-week repurchase restriction)
- Revenue — Tax and Duty Manual Part 19-04-03, disposals of marketable shares and securities (section 581 TCA 1997)
- Revenue — Tax and Duty Manual Part 19-02-05, allowable losses (section 546 TCA 1997)
- Revenue — If you make a loss
- Revenue — Notes for Guidance, Taxes Consolidation Act 1997 Part 19
This is general information, not tax advice.
This guide explains Irish tax rules in general terms. It is not tax, financial, accounting or legal advice, and it does not take account of your individual circumstances. Vantanomic is not a tax adviser, accountant or financial adviser, and is not authorised or regulated by the Central Bank of Ireland.
Tax rules change and reliefs depend on your own situation. While we take care to keep this page accurate and up to date, we do not warrant that it is, and you should satisfy yourself as to its correctness before acting on it. Check your position with Revenue (revenue.ie) or a qualified professional. To the extent permitted by law, we accept no liability for any loss arising from reliance on this page.
Last reviewed: 10 August 2026.