Scroll through a fund's available share classes on a UK investment platform and it is common to see the same fund listed twice — once marked "Acc" and once marked "Inc". These stand for accumulation and income units, and the difference between them, while simple in mechanics, has real consequences for how convenient a fund is to hold and, outside a tax wrapper, how it is taxed. Choosing the right one for a given account is a small decision that is easy to get wrong by default.
The basic mechanical difference
Funds that hold dividend-paying shares or interest-paying bonds generate income from those underlying investments. What happens to that income depends on the share class chosen:
- Income (Inc) units pay the income out to the investor, typically as cash paid into their account, on a set schedule — quarterly, half-yearly or monthly, depending on the fund.
- Accumulation (Acc) units do not pay the income out. Instead, the income is automatically reinvested within the fund, increasing the value of each unit rather than paying cash to the investor.
Both share classes represent exactly the same underlying investments and the same underlying fund manager and strategy — the only difference is what happens to the income the fund generates.
Why the choice matters inside a tax wrapper
Within an ISA or a SIPP, income and gains are not subject to UK income tax or Capital Gains Tax, so the choice between Acc and Inc units is largely a matter of convenience rather than tax efficiency.
- An investor who wants their portfolio to grow automatically without manually reinvesting cash distributions may prefer accumulation units, since reinvestment happens within the fund without any action required.
- An investor drawing an income from their ISA or SIPP — for example, a retiree in drawdown — may prefer income units, since the cash is paid out directly and can be used to fund withdrawals without needing to sell fund units.
Why the choice matters more outside a tax wrapper
In a general investment account, outside an ISA or SIPP, dividend income is potentially subject to income tax, and outside the £500 annual dividend allowance for the 2025/26 tax year, dividend income is taxed at rates depending on the investor's income tax band. This applies whether the income is taken as cash (income units) or automatically reinvested (accumulation units) — reinvestment does not avoid the tax liability, since HMRC treats the reinvested income as having been received for tax purposes regardless of the share class.
The key practical difference outside a wrapper
Because accumulation units reinvest income automatically without an additional purchase transaction appearing on the account statement in the same visible way income units' payouts do, investors sometimes overlook that this reinvested income is still taxable, potentially leading to under-reporting on a Self Assessment tax return. It is important to keep records of the "notional distribution" reported by accumulation funds, since this is the taxable amount, even though no cash was received.
A further complication: base cost for Capital Gains Tax
Reinvested income within an accumulation unit increases the effective "base cost" of the holding for Capital Gains Tax purposes, since that income has already been taxed as income and should not also be taxed again as a capital gain when the units are eventually sold. Keeping accurate records of notional distributions over time is important for correctly calculating any CGT due on a future sale, since the £3,000 annual CGT exempt amount and the 18%/24% rates for basic and higher/additional rate taxpayers apply to whatever gain remains after this adjustment.
| Factor | Accumulation (Acc) units | Income (Inc) units |
|---|---|---|
| Cash paid out | No — income reinvested automatically | Yes — paid to investor on a set schedule |
| Convenience for reinvesting | High — happens automatically within the fund | Requires investor to manually reinvest cash if desired |
| Suits income drawdown | Less directly — units may need selling to generate cash | Well — cash income arrives without needing to sell units |
| Tax treatment outside a wrapper | Notional distribution still taxable as income; increases CGT base cost | Cash distribution taxable as income in the usual way |
| Tax treatment inside ISA/SIPP | No income or capital gains tax either way | No income or capital gains tax either way |
Choosing between them by account type
- Within an ISA, accumulating for growth: accumulation units are often chosen for simplicity, avoiding the need to manually reinvest small cash distributions.
- Within an ISA or SIPP, drawing an income: income units are often preferred, since the cash arrives directly and can fund withdrawals without needing to sell holdings.
- In a general investment account, accumulating for growth: either can work, but accumulation units require careful record-keeping of notional distributions for tax purposes.
- In a general investment account, wanting income: income units are typically more straightforward, since the cash distribution is clearly visible and easier to track for tax purposes than a notional distribution.
How Acc and Inc units affect unit price directly
It is worth understanding a mechanical detail that sometimes confuses investors comparing the two share classes: because accumulation units reinvest income directly into the fund, their unit price rises over time by more than an equivalent income unit's price would, all else being equal, since accumulation units are effectively continuously buying more of the fund with the retained income. Income units' unit price, by contrast, typically shows a small, regular drop immediately after each distribution is paid out, reflecting the cash that has just left the fund. This means comparing the historical unit price growth of Acc and Inc share classes of the same fund directly, without accounting for the income paid out by the Inc units along the way, is not a fair like-for-like comparison of total return — the Inc units' total return needs to include the cash distributions received, not just the unit price change, to be properly comparable.
Historic versus notional distributions on a factsheet
Fund factsheets and platform statements for accumulation units typically report a "notional distribution" figure, sometimes called an "equalisation" amount in the first period after a fund purchase, reflecting the income that has been reinvested on the investor's behalf during the period. Understanding this figure, and where to find it — usually in the annual or half-yearly consolidated tax voucher or platform tax statement for investments held outside an ISA or SIPP — is important for accurately completing a Self Assessment tax return where required, since HMRC expects this notional income to be reported even though no cash was physically received by the investor.
Switching between share classes
Many platforms allow switching between the Acc and Inc share classes of the same fund. Within an ISA or SIPP, this switch typically has no tax consequence. Outside a wrapper, switching share classes can, depending on the platform's mechanics, be treated as a disposal for Capital Gains Tax purposes, so it is worth checking this before switching an existing taxable holding.
A worked example
Suppose a hypothetical investor holds £25,000 in the accumulation units of a UK equity income fund within a general investment account, and the fund reports a notional distribution of £750 for the year. Even though no cash was paid to the investor, this £750 is treated as dividend income for tax purposes. After the £500 annual dividend allowance, £250 would be subject to income tax at the investor's applicable dividend tax rate. The investor should also note the £750 as an addition to the base cost of their holding, so that if they later sell the units, this amount is not taxed again as part of any capital gain.
A note on availability
Not every fund offers both an accumulation and an income share class — some smaller or more specialist funds may only offer one or the other, particularly funds not primarily marketed around income generation. Where only an accumulation share class is available and an investor specifically wants a cash income, they may need to either choose a different fund offering both share classes, or manually sell a small number of units periodically to generate cash — though this manual approach converts what would otherwise be income into a disposal for Capital Gains Tax purposes outside a wrapper, adding a further layer of complexity worth avoiding where a suitable income share class is available instead.
A summary decision guide
Faced with the choice on a platform's fund purchase screen, a useful shorthand is to ask two questions: first, is this holding inside a tax-free wrapper or a taxable account, and second, do I want the income paid out as cash or reinvested automatically? Inside a wrapper, the second question is really the only one that matters, since tax treatment is unaffected either way. Outside a wrapper, both questions matter — the tax treatment applies regardless of the answer to the second question, but the practical record-keeping burden differs noticeably between the two share classes, with income units generally being the simpler of the two to track correctly for tax purposes over time.
Key takeaways
- Accumulation (Acc) units reinvest income automatically within the fund; income (Inc) units pay it out as cash.
- Inside an ISA or SIPP, the choice is mainly about convenience, since neither income nor gains are taxed either way.
- Outside a wrapper, reinvested income in accumulation units is still taxable, even though no cash is received — this is easy to overlook.
- Reinvested income in accumulation units increases the CGT base cost of the holding, which matters for calculating any future gain correctly.
- Income units are often more straightforward for retirees or others drawing a regular income from their portfolio.
- Always check current HMRC and FCA figures and allowances, as these change from tax year to tax year.