Two versions of the same fund
Most funds come in two flavours: income (Inc) units, which pay dividends out to you as cash, and accumulation (Acc) units, which automatically reinvest those dividends back into the fund. Same fund, same holdings, same charges — the only difference is what happens to the income.
That small difference matters more than it looks.
Why accumulation units suit long-term investors
Reinvested dividends are a surprisingly large share of long-run stock market returns — over multi-decade periods, roughly half of the total return of a broad index comes from dividends being reinvested and compounding, not from prices rising.
You can reinvest income units manually, but in practice this fails in small ways that add up: cash sits idle between dividend dates, small amounts feel too trivial to reinvest, some platforms charge dealing fees on each reinvestment, and every manual step is an opportunity to not bother. Accumulation units remove all of that. The dividend never appears as temptingly spendable cash; it is already back at work the day it’s paid.
For anyone in the growth phase of their investing life — still earning, still adding money, a decade or more from spending it — accumulation units are almost always the right default.
The tax quirk to understand
Inside an ISA or pension, none of this matters for tax: dividends are tax-free either way, and Acc units are simply the convenient choice.
In an unwrapped account (a general investment account, or GIA), there is a trap worth knowing: accumulated dividends are still taxable, even though you never see the cash. HMRC treats the reinvested amount (“notional distributions” for funds, “excess reportable income” for ETFs) as income you received, and it counts against the £500 dividend allowance. You also need to track these amounts, because they increase your cost base for capital gains purposes — miss that, and you’ll eventually pay tax twice on the same money. The GIA survival guide covers the whole unwrapped tax picture.
Practical rules of thumb:
- ISA or pension → Acc units. No paperwork, maximum compounding.
- GIA with modest amounts → Acc still fine, but keep your platform’s tax reports each year.
- GIA with large amounts → consider Inc units. The visible cash makes tax reporting straightforward, and you can sweep it back in (or into your ISA) yourself.
When income units are the right choice
Accumulation is for building; income units earn their keep when you’re spending. In retirement, Inc units turn your portfolio into a natural cash flow — dividends arrive as money you can live on without selling anything, which pairs well with a drawdown strategy (see the drawdown guide). Many investors sensibly hold Acc units for decades and switch to Inc versions of the same funds as retirement approaches. Platforms treat this as a switch between unit classes; inside a wrapper it has no tax consequence.
The one-line summary
While you’re building wealth, choose “Acc” and let compounding run without friction. Once you’re living off the money, “Inc” turns the same portfolio into an income. And keep the whole thing inside an ISA or pension so the choice never creates a tax problem.
Related guides & tools
- Low-cost index fund investing — the fund to buy Acc units of in the first place
- ISA investing — the UK’s best tax shelter — the wrapper that makes the tax quirk irrelevant
- Investing outside ISAs — notional distributions, ERI and the GIA paperwork in full
- Retirement drawdown — where switching to Inc units earns its keep
Last reviewed: July 2026.