Open almost any UK fund on Hargreaves Lansdown, AJ Bell, or Vanguard and you will be offered the same fund twice, with two near-identical names. One ends in "Acc" and one ends in "Inc". Most people pick whichever sits at the top of the list, or whichever the platform pre-selects, and never think about it again. For an investor holding inside an ISA that shrug is mostly harmless. Outside an ISA, in a general investment account, picking on autopilot can hand you a tax problem that quietly grows every year you ignore it.
The two share classes hold exactly the same underlying investments, charge the same ongoing fee, and track the same performance. The only difference is what happens to the income — the dividends from shares or the coupons from bonds — that the fund generates along the way. That single difference is small in a tax wrapper and surprisingly large outside one.
What the two actually do
An income unit (Inc) pays the income out to you. Every quarter, or twice a year depending on the fund, the dividends collected from the holdings are distributed as cash, either landing in your account to spend or sitting there waiting for you to do something with it. The price of the unit reflects only the capital value of the investments, because the income has been handed over.
An accumulation unit (Acc) keeps the income inside the fund and reinvests it automatically. You receive nothing in cash; instead, the value of each unit rises to reflect the income that has been rolled back in. Over years, this is the quiet engine of compounding — your reinvested dividends start earning returns of their own — and you never have to lift a finger or pay a dealing charge to make it happen.
Performance over the long run ends up very similar between the two, assuming the income from the Inc version is reinvested. The difference is purely mechanical: one does the reinvesting for you, the other leaves it in your hands.
Which one suits which goal
The honest rule of thumb is straightforward. If you are building wealth and do not need the cash now, choose accumulation. It compounds automatically, it saves you the hassle and the dealing cost of manually reinvesting every distribution, and it is the cleaner choice for a long-term Stocks and Shares ISA where tax does not complicate things.
If you are drawing an income — you are retired, or you want the dividends to live on — income units make life simpler. The cash arrives in your account ready to use, and you can see exactly what your portfolio is paying you without having to sell units to free up money. For a retiree running a dividend portfolio, watching real cash land each quarter is psychologically and practically easier than selling slices of an accumulating fund.
There is a middle case worth naming. Some investors in the building phase deliberately choose income units inside an ISA so they can pool the dividends and direct them toward whichever holding is cheapest or most underweight, rather than mechanically topping up the fund that paid them. That is a perfectly valid active habit — it just takes discipline, because uninvested cash sitting in your account is a quiet drag on returns.
The tax trap nobody mentions
Here is where the choice stops being cosmetic. Inside an ISA or a SIPP, none of this matters for tax — your gains and income are sheltered either way, so you can pick on convenience alone. The problem lives in a general investment account, where you are exposed to dividend tax and capital gains tax.
The thing that catches people out: with accumulation units, the reinvested income is still taxable as income, even though you never received a penny of cash. HMRC treats those rolled-up distributions exactly as if they had been paid to you and you had chosen to reinvest. The fund reports them as "notional distributions", and they count against your annual dividend allowance — which for the 2026/27 year has been ground down to just £500, a fraction of the £2,000 it was a few years ago. So you can owe dividend tax on money you cannot see, did not spend, and might not even realise exists.
It gets fiddlier at sale. When you eventually sell accumulation units in a GIA, those reinvested distributions form part of your cost base — what HMRC calls "equalisation" and "accumulated income". If you forget to add them, you overstate your gain and overpay capital gains tax, especially relevant now that the annual CGT exemption has fallen to £3,000. Working out the correct figure means keeping every year's distribution statements, because the platform will not always do the sum for you.
Income units sidestep most of this mess. The distribution is paid in cash, it is obvious, it is reported clearly, and your capital gains calculation is cleaner because there are no notional amounts buried inside the unit price. For that reason alone, plenty of seasoned investors deliberately hold income units in their GIA and accumulation units in their ISA — the wrapper decides, not habit.
What to do this week
Log into your platform and look at what you actually hold. If everything is sitting in an ISA, you can relax — accumulation is usually the sensible default and there is nothing to fix. If you hold funds in a general account, check whether they are Acc or Inc, and ask yourself whether you have been declaring those notional distributions. If you have a few years of accumulation units in a GIA and have never thought about the reinvested income, it is worth a conversation with an accountant before it compounds into a real liability.
Switching between the two share classes within the same fund is usually treated as a "conversion" rather than a sale on most UK platforms, which means it does not trigger a capital gains event — a useful detail if you decide you are in the wrong class. Check that your provider handles it as a conversion before you act, because not all do, and the last thing you want is to crystallise a gain solving a tax problem. The choice between two letters on a fund name is one of the smallest decisions on your platform. In a taxable account, it is also one of the few that can come back to bite you years later.
ETFs, dividend dates, and the details that trip people up
The Acc-versus-Inc split is not limited to old-style funds. Exchange-traded funds carry the same distinction — a global tracker like the ones from Vanguard, iShares, or HSBC will often have both a distributing and an accumulating version, sometimes marked "Dist" and "Acc" instead. The mechanics are identical, and so is the GIA tax trap: an accumulating ETF held outside a wrapper still generates taxable income you never see in cash, and for offshore-domiciled ETFs there is an extra layer to check, because a fund without UK "reporting status" can have its gains taxed as income rather than at the kinder capital gains rates. Sticking to reporting funds matters more than most beginners realise.
There is also a timing quirk worth understanding. Funds have an "ex-dividend" date, and if you buy income units shortly before it, part of what you pay is effectively the income about to be paid out — you get the distribution back almost immediately, but it can muddy your sense of performance in the first few weeks. Accumulation units sidestep that confusion because nothing is paid out. None of this should drive your decision on its own, but it explains why a newly bought income fund sometimes seems to "drop" right after a distribution: the price simply reflects the cash that just left.
Step back from the detail and the principle is simple. Decide what you want the income to do — compound quietly or arrive as spendable cash — and then let the tax wrapper, not habit or the platform's default sort order, pick the share class. Accumulation in the ISA, income in the taxable account, and a clear record of every distribution if you do end up holding Acc units in a GIA. Do that once, and the smallest decision on your platform stops being the one that surprises you at tax time.