FTSE 100 ISA Returns: What £20,000 Grew to Over Five Years

A £20,000 investment in a FTSE 100 ISA returns scenario, using a broad-market index fund held inside a Stocks and Shares ISA from 28 August 2021 to 28 August 2026, would have compounded to £36,264, according to total return data covering both capital gains and reinvested dividends.

The FTSE 100’s points total moved from 7,148 to 10,808 over the period, a price gain of just over 50%. Add in dividends, which the index distributes at a yield currently sitting at 3.05% as at 28 August 2026 per FTSE Russell data, and the total return over the five years reaches 81.32%, equivalent to 12.6% annualised. The average yearly gain on the initial stake came in at over £3,000.

For context, a Cash ISA over the same period would likely have returned somewhere in the 3% to 4% range annually. The difference in outcomes, after five years, is substantial.

Why FTSE 100 ISA Returns Were Unusually Strong in This Period

The five years from 2021 to 2026 represent something of a hot streak. The long-run picture is more measured. According to IG International’s analysis of FTSE 100 data from 2003 to 2023, the index delivered a total return of 241% over twenty years, equivalent to 6.3% annualised including dividends. Strip out average inflation of 2.8% over that period and the real annualised return falls to 3.5%.

That longer arc matters for anyone extrapolating from recent performance. The 81.32% five-year total return sits well above the historical average, and projecting that same trajectory forward is a stretch. Even the S&P 500 has not sustained above 11% annualised over multiple decades.

Income, however, remains a structural support. AJ Bell’s dividend dashboard forecasts FTSE 100 total dividend payments for 2026 at a forward yield of 3.3%, and with share buybacks included, the index is expected to return £117.4bn in total cash to investors during 2026, equivalent to 4.4% of the index’s £2.7tn market capitalisation. Roughly half of the index’s long-term total return has historically been composed of dividends, per LSEG’s FTSE Russell methodology, which measures the total return index by reinvesting income on the dividend ex-date.

Aviva: A Standout Contributor to FTSE 100 Gains

Among individual constituents, Aviva (LSE: AV.) has been one of the more consequential contributors to FTSE 100 outperformance in this period. The share price rose 79% over the five years, while the dividend yield over the last twelve months stood at 5.53%.

The company’s 2025 Results Announcement, published 5 March 2026, reported full-year operating profit of £2,203m, up 25% from £1,767m in 2024. Operating earnings per share reached 56.0p, up 17% from 48.0p, and the IFRS return on equity came in at 17.5%, a rise of 1.8 percentage points from 15.7% in 2024.

Part of that uplift traces directly to the acquisition of Direct Line Group plc, completed on 1 July 2025. The 2025 results include six months of Direct Line’s contribution, giving the headline operating profit figure a structural boost that will not recur on a like-for-like basis in 2026.

Total dividends for 2025 came to 39.3 pence per share, up from 35.7 pence in 2024. The final dividend for 2025 was 26.2 pence per share, compared with 23.8 pence the prior year. Management has guided for mid single-digit growth in the cash cost of the dividend going forward, and the Aviva dividends page confirms a 14.0 pence interim dividend for the 2026 financial year, with a payment date of 15 October 2026.

On the analyst side, Morgan Stanley moved Aviva to Equal Weight from Overweight, setting a price target of 670 GBp, while Deutsche Bank maintained a Buy rating, per market commentary aggregated by Yahoo Finance. The Equal Weight move from Morgan Stanley reflects a view that near-term upside has been largely captured, even as the underlying operational momentum remains intact.

Aviva’s guidance for its UK general insurance business includes a combined operating ratio below 94% for full-year 2026, subject to normal weather conditions, which would indicate continued underwriting discipline after the Direct Line integration. The next test is whether the enlarged group can sustain that operational ratio through 2026 and into 2027 as one-off acquisition synergies are absorbed into the run rate.

For an ISA investor who held through the last five years, the tax-free compounding has done most of the work. The question for the next five is whether the FTSE 100’s income engine, rather than capital appreciation, carries the heavier load — and whether Aviva’s post-acquisition earnings cadence justifies the current valuation.