We’re told a Stocks and Shares ISA saves tax – but how much, really? For a small, low-yield portfolio, the answer can feel underwhelming.
With a high-yield holding such as Greencoat UK Wind (LSE:UKW) though, reinvested dividends and regular contributions can make the benefit compound quickly.
With a yield upwards of 9% and dividend growth averaging 5.3% annually for 13 consecutive years, it’s easy to see why. Plus, its recent half-year results reported dividend cover of 1.9x, with full-year net cash generation guided towards the top end of £350m-£410m.
Still, dividends are never guaranteed, so let’s dig a little deeper and see what the real benefits are.
Please note that tax treatment depends on the individual circumstances of each client and may be subject to change in future. The content in this article is provided for information purposes only. It is not intended to be, neither does it constitute, any form of tax advice. Readers are responsible for carrying out their own due diligence and for obtaining professional advice before making any investment decisions.
Setting the stage
Imagine an investor puts £10,000 into Greencoat UK Wind at the current price of around 117.6p per share, with a yield of roughly 9.1%. The example assumes the 10.7p dividend target holds, the share price stays flat, and you reinvest every dividend.
Outside an ISA, the dividend allowance covers the first £500 of income. Above that, dividend tax is 10.75% for basic-rate taxpayers and 35.75% for higher-rate taxpayers in 2026/27.
Reinvestment is where the ISA starts to earn its keep. Each dividend buys more shares, with those extra shares generating further dividends.
| Holding period | Portfolio value | Reinvested dividends | Tax saved: basic | Tax saved: higher |
|---|---|---|---|---|
| 5 years | £15,458 | £5,458 | £318 | £1,058 |
| 10 years | £23,896 | £13,896 | £956 | £3,180 |
| 20 years | £57,103 | £47,103 | £3,989 | £13,264 |
After 20 years, a higher-rate taxpayer could avoid roughly £13,264 of dividend tax on dividends received. Of course, this is just illustrative – in reality, the yield and price would fluctuate and results would differ.
If Greencoat UK Wind’s share price grows, the additional capital gains could matter just as much as the dividends.
Adding £100 a month
Now suppose the investor starts with £10,000 and adds £100 every month (£1,200 a year), with all dividends reinvested.
| Holding period | Total invested | Portfolio value | Investment growth | Tax saved: basic | Tax saved: higher |
|---|---|---|---|---|---|
| 5 years | £16,000 | £22,655 | £6,655 | £447 | £1,485 |
| 10 years | £22,000 | £42,217 | £20,217 | £1,636 | £5,440 |
| 20 years | £34,000 | £119,202 | £85,202 | £8,084 | £26,885 |
The contrast is striking. Over 20 years, the investor contributes an extra £24,000, while the portfolio could reach about £119,202. A higher-rate ISA holder would avoid an estimated £26,885 of dividend tax.
The biggest driver isn’t clever stock-picking. It’s time, reinvestment, and consistent monthly contributions.
My take
Yes, a Stocks and Shares ISA really can save serious money – but mainly for investors who give it time. For a basic-rate taxpayer, the dividend-tax saving is useful rather than transformative.
For a higher-rate taxpayer considering an income stock such as Greencoat UK Wind, the ISA wrapper becomes a powerful compounding tool.
The practical message is simple: invest early in the tax year, reinvest dividends automatically, and let tax-free compounding do the heavy lifting.
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Mark Hartley does not hold any positions in the companies mentioned.
