Best Investment Platforms for Interest on Cash UK (2026)

What do I need to know about Compound Interest?

What is compound interest and how does it work?

Compound interest means earning interest on both your initial investment and previous returns. Over time, this snowball effect accelerates growth. For UK investors, compounding applies to savings accounts, ISAs, pensions, and reinvested dividends, making time in the market more important than short-term gains.

Why is compound interest powerful for UK investors?

Compound interest builds wealth because growth accelerates the longer money stays invested. Even modest returns multiply significantly over decades. UK investors benefit most when they reinvest dividends and interest automatically, letting the compounding process magnify gains without needing to add large additional contributions.

How is compound interest different from simple interest?

Simple interest is calculated only on the initial amount, while compound interest applies to both the principal and accumulated returns. Over time, compounding delivers far larger growth. For UK savers and investors, this difference determines whether money simply keeps pace with inflation or outpaces it.

Compound Interest over Time

Compounding: Cash vs S&P 500 vs Inflation (1975–2025)

Assumes £10,000 starting balance and constant annual rates: Cash 2.5%, UK inflation 3%, S&P 500 total return 10% adjusted for inflation.

The chart compares £10,000 invested since 1975. Cash ISAs compounded at 2.5% but failed to keep pace with 3% inflation. The inflation-adjusted S&P 500 compounded at about 6.8% annually, showing significant real growth. It highlights why long-term equity exposure outperforms cash savings.

Compound Interest Calculator

Best Compound Interest Investments in the UK

What are my options as a UK investor?

UK investors can choose between fixed-rate savings products, such as Cash ISAs, or market-based investments like index funds, ETFs, REITs, and pensions. Fixed products provide certainty but weaker long-term growth. Market exposure typically outpaces inflation, delivering stronger compounded returns across decades.

Fixed Rate vs Market Investments

Fixed-rate accounts offer guaranteed but limited growth, often below inflation. Market investments carry risk but provide higher returns over time. Choosing between them depends on risk tolerance and goals. Long-term investors seeking real wealth growth usually benefit most from diversified, low-cost, market-based strategies.

Interest vs Inflation: Does Cash Keep Pace?

Cash accounts rarely beat inflation in the UK. Even at 3% annual interest, long-term inflation erodes purchasing power. By contrast, equity investments historically average higher returns, allowing compounding to build real wealth. For long-term growth, markets outperform cash, though savings remain useful for safety.

Which accounts support compound interest in the UK?

Accounts supporting compounding include Cash ISAs, Stocks & Shares ISAs, workplace pensions, and SIPPs. These accounts often allow reinvestment of interest or dividends. Tax efficiency further enhances compounding, particularly in ISAs and pensions, where gains are shielded from income and capital gains taxes.

How do Cash ISAs work for compounding?

Cash ISAs earn interest on deposits, with returns reinvested automatically. Compounding occurs annually or monthly, depending on the provider. While secure and tax-free, long-term returns usually lag inflation, limiting their effectiveness as a wealth-building vehicle compared to equity-based investments.

How often is interest compounded in an ISA?

Most UK banks compound ISA interest annually, though some accounts calculate monthly. The frequency matters less than the rate itself. Even with monthly compounding, low returns mean Cash ISAs often fail to protect long-term purchasing power against inflationary pressures.

Investment Types for Compound Growth

Are Stocks & Shares ISAs good for compound interest?

Yes. Stocks & Shares ISAs allow reinvestment of dividends and gains into funds, ETFs, or shares. Compounding works powerfully over decades, particularly with index funds. Returns are tax-free, making ISAs one of the most efficient long-term compounding vehicles for UK investors.

Can dividends be reinvested to create compounding?

Yes. Reinvesting dividends means each payout buys more shares, which then produce further dividends. Over time, this snowball effect significantly increases growth. Most UK platforms allow dividend reinvestment plans (DRIPs), which automate the process inside Stocks & Shares ISAs.

Why index funds are powerful for long-term growth

Index funds track markets cheaply, spreading risk across hundreds of companies. By reinvesting dividends, investors benefit from market-wide compounding at minimal cost. In a Stocks & Shares ISA, this approach grows wealth tax-free, historically outperforming inflation and fixed-rate accounts over decades.

Are REITs a good compound interest investment?

REITs pay dividends from property income, which can be reinvested. They offer diversification into real estate and regular income streams. However, they carry market risk, are sensitive to interest rates, and may be more volatile than other compounding investment choices.

Do REITs pay dividends that can be reinvested?

Yes. REITs must distribute most income as dividends. Investors can reinvest these payouts, creating compounding growth over time. Many UK platforms support automatic reinvestment through dividend plans, helping build exposure to property markets without directly owning physical assets.

What are the risks of compounding through property funds?

REITs can be volatile during downturns, as property values and rental income fluctuate. Rising interest rates may reduce profitability. While dividends support compounding, risks make REITs better suited as part of a diversified portfolio, not as a sole compounding vehicle.

Can ETFs provide compound interest returns?

Yes. Dividend-paying ETFs reinvest or distribute income. By reinvesting, compounding accelerates growth. ETFs track global or UK indices, offering broad diversification at low cost. Over decades, ETF compounding typically outpaces inflation, especially when held tax-efficiently in an ISA or pension.

How do dividend-paying ETFs enable compounding?

Dividend-paying ETFs distribute earnings from their underlying holdings. Reinvested dividends buy more ETF units, which generate further income. Over time, this cycle compounds returns, amplifying wealth growth compared to simply holding the ETF without reinvestment.

Are global ETFs better than UK-only options for compounding?

Global ETFs spread risk across markets and sectors, often delivering stronger compounding by capturing worldwide growth. UK-only ETFs may limit exposure to higher-growth regions. For most investors, global diversification improves long-term compounding while reducing reliance on a single market's performance.

Can bonds and gilts provide compound interest?

Yes, though growth is modest. Bonds and gilts pay interest, which can be reinvested to generate compounding. Returns are typically lower than equities but provide stability. They are often used as part of diversified portfolios to balance risk and support steadier growth.

What about corporate bonds with reinvested coupons?

Corporate bonds often offer higher yields than government gilts. Reinvesting coupon payments allows compounding over time. However, credit risk and defaults are considerations. Corporate bonds can add diversification and enhance compounding when balanced with equities in a long-term portfolio.

Are pension accounts (SIPPs, workplace pensions) compound interest investments?

Yes. Pensions benefit from long-term compounding of contributions, investment growth, and reinvested dividends. Tax relief and employer contributions accelerate growth further. SIPPs and workplace pensions are among the most effective ways for UK investors to harness compounding over decades.

How does compounding work inside a pension account?

Pension contributions are invested in funds that generate returns. Reinvested dividends and capital growth compound over time. Tax relief boosts contributions upfront, making pensions especially powerful for long-term compounding, provided investors remain invested consistently.

What role does employer contribution play in compounding?

Employer contributions significantly increase pension growth. Combined with tax relief, they create a compounding effect on both contributions and returns. Over decades, this triple boost makes pensions one of the strongest wealth-building vehicles for UK investors.

Strategies to Maximise Compound Interest

How long should you invest for to benefit from compounding?

The longer you stay invested, the more powerful compounding becomes. Over 20–30 years, even modest annual returns multiply significantly. Short-term investments rarely capture the full benefits, making long-term consistency essential for maximising compounded growth.

How much difference does starting early make?

Starting early drastically improves results. A small monthly investment begun in your twenties compounds into far greater wealth than larger contributions begun later. Time is the most critical factor, outweighing short-term market fluctuations or small changes in contributions.

Should you reinvest dividends and interest automatically?

Yes. Reinvesting dividends and interest ensures compounding occurs seamlessly. Automatic reinvestment eliminates missed opportunities and accelerates long-term growth. UK investors should opt for dividend reinvestment plans in ISAs and pensions to maximise efficiency and consistency.

How do fees and taxes affect compound returns?

High fees erode compounding by reducing the base on which returns grow. Taxes on gains or dividends further weaken growth. Using tax-efficient accounts such as ISAs and pensions, combined with low-cost funds, preserves more of the compounding effect over time.

Risks of Compound Interest Investments

Are all compound interest investments safe?

No. Cash ISAs are safe but deliver low returns. Market investments carry risk, including volatility and capital loss. Diversification, time in the market, and using tax-efficient accounts reduce risk, but investors must balance safety with the need to outpace inflation.

Can inflation reduce the effect of compounding?

Yes. Inflation erodes purchasing power, reducing the real value of compounded returns. Cash investments rarely keep pace, making equities and diversified funds more effective long-term. Beating inflation is crucial for compound interest to build real wealth.

What are the risks of compounding in stock-based investments?

Market downturns can reduce portfolio value, slowing compounding. Dividends may be cut, and short-term losses occur. However, over long horizons, diversified stock investments historically recover and deliver compounding that outpaces inflation, provided investors stay disciplined and invested.

Final Thoughts

Compound interest is most powerful when combined with time, reinvestment, and tax efficiency. While cash savings provide security, they rarely beat inflation. For long-term UK investors, Stocks & Shares ISAs with index funds, pensions, and ETFs offer the strongest compounded growth, building wealth steadily across decades.

1. Stocks & Shares ISAs with Global Index Funds – Tax-free growth, dividend reinvestment, and diversification make this the most effective compounding vehicle.
2. Workplace Pensions and SIPPs – Employer contributions plus tax relief amplify compounding for retirement savings.
3. Dividend-Paying ETFs – Low-cost global exposure with automatic reinvestment supports long-term compounding.
4. REITs in an ISA – Regular property income reinvested can compound steadily, though more volatile.
5. Government and Corporate Bonds – Lower growth but stability, useful alongside equities to balance compounding strategies.

FAQs

References

1. GOV.UK – Individual Savings Accounts (ISAs)
2. MoneyHelper – Compound Interest Explained
3. Bank of England – How Interest Rates Affect You
4. Vanguard UK – Investing for the Long Term
5. Hargreaves Lansdown – What is a SIPP?