What is the ISA allowance for 2025/26?

The annual ISA allowance is £20,000. You can split this between a cash ISA and stocks & shares ISA. Any growth within the ISA is completely tax-free.

Are the returns in this calculator realistic for UK investors?

The default 7% represents a typical long-term average for a diversified global equity portfolio. Cash savings typically return less (4–5%). Use the rate slider to model your specific situation.

Should I use a cash ISA or stocks & shares ISA?

For short-term goals (under 5 years), a cash ISA is safer. For long-term growth (5+ years), a stocks & shares ISA has historically delivered significantly better returns despite short-term volatility.

How often should interest compound?

More frequent compounding (monthly or daily vs yearly) gives slightly better results, but the difference is usually small. Most savings accounts compound daily, while investments like index funds compound based on market returns.

Should I account for inflation?

Yes — inflation erodes purchasing power over time. Use the Advanced Settings to add an inflation rate (2–3% is typical for the UK) to see your results in today's money. This gives a more realistic picture of future wealth.

What's the best strategy for compound growth?

Start early, contribute consistently, and let time do the work. Even small amounts grow significantly over decades. Increasing your contributions by a small percentage each year (use Advanced Settings) can dramatically boost your final balance.

UK Investing

UK Compound Interest
Calculator (2026)

See how small monthly savings can grow into life-changing money

Calculate your savings growth using UK-focused assumptions — ISA allowances, realistic returns, and monthly contributions in pounds sterling.

Free to useNo signup requiredUsed by UK investors

1Calculate

2Understand

3Take action

Starting amount

£0£20k£200k

Monthly contribution

£0£1k£5k

Expected annual return

Time horizon

yrs

Final Balance

£410,761

After 25 years

You Put In

£151,000

Your own money

Interest Earned

£259,761

Earned passively

You could reach £410,761 — investing tax-free can help you get there

Your money vs compound growth63% from interest

ContributionsCompound interest

To reach £410,761, most UK investors use a Stocks & Shares ISA to invest £500/month tax-free.

Returns depend on the underlying investments and are not guaranteed.

Your £500/month fits within the £20,000 ISA allowance

All growth inside an ISA is tax-free. Start from as little as £1.

Capital at risk when investing

Thousands of UK investors use this calculator monthly

Start investing tax-free ↓

Compare scenarios

See how different choices change your outcome

Growth Over Time

Quick Scenarios

Your Personalised Insights

Year 18: your interest overtakes your contributions. From here, compounding does the heavy lifting.
Your money earns ~£28/day in interest — that's £259,761 earned while you sleep.
Saving just £50 more per month would add £40,504 to your final balance — that's £15,000 invested for £40,504 extra.
5 more years would add £207,341 — nearly 50% more, showing how powerful time is.
Starting 5 years earlier would add £146,259 to your final balance. Every year you wait costs real money.Start investing now →
Consistency beats timing — investing £500/month for 25 years matters more than picking the perfect moment to start.
At your current plan, you reach £250k in 20 years. That's a real milestone — and it compounds from there.Start building towards it →

Next Steps

Affiliate disclosure: Some links below are affiliate links. We may earn a commission at no extra cost to you if you sign up. This does not influence which platforms are shown or how they are described.

Explore popular UK investment platforms

Many UK investors hold investments in a stocks & shares ISA for tax efficiency. Returns depend on the investments held within the ISA and are not guaranteed. Here are popular platforms available to UK investors.

FCA regulatedFree to openTax-free ISA growth

Platform	Min. invest	Fees	ISA	Best for
Trading 212	Start from £1	No commission	Yes	Beginner-friendly
Revolut	No minimum	Free plan available	Yes	All-in-one finance
Estateguru	Start from €50	No investor fees	—	Property-backed lending

Trading 212

Suited for: Beginner-friendly

Commission-free stocks & shares ISA. Clean app, no hidden charges, perfect for getting started.

Most popular choice for UK investors starting small

No commission on stocks1M+ UK usersFree ISA included

No commissionStart from £1FCA regulatedGet started free →

All-in-one appAffiliate

Revolut

Suited for: All-in-one finance

All-in-one finance app with savings vaults, stock trading, crypto, and multi-currency accounts. Great for everyday money management.

40M+ global usersInstant account setupSavings + investing in one app

Free plan availableNo minimumFCA regulatedGet started free →

Property-backed lendingAffiliate

Estateguru

Suited for: Property-backed lending

European property-backed lending platform. Returns are not guaranteed and your capital is at risk. Past performance is not a reliable indicator of future results.

Property-secured loansAuto-invest available

P2P lending is high risk. You could lose some or all of your money. Not covered by the FSCS.

No investor feesStart from €50Licensed by Estonian Financial Supervision AuthorityGet started free →

Capital at risk. These are informational suggestions, not financial advice.

Invest from £1 tax-free

Capital at risk

Start investing →

Try These Scenarios

ISA Compound Interest Calculator — Tax-Free GrowthCalculate tax-free compound interest growth in a UK stocks & shares ISA. See how ISA investing compounds over time.Lifetime ISA (LISA) Calculator — 25% Government BonusCalculate Lifetime ISA growth including the 25% government bonus. See how LISA contributions compound for first homes or retirement.Save for a House Deposit — Compound Interest CalculatorCalculate how quickly you can save for a house deposit using compound interest. See how monthly savings grow over 3–10 years.

Explore All Scenarios

Browse pre-built calculators by category.

What If You Invest £50 Per Month?See how even £50 per month compounds into real wealth over time. Free calculator with visual charts and year-by-year breakdown.What If You Invest £100 Per Month?See how investing £100 per month grows over time with compound interest. Calculate your projected returns with our free tool.Invest £200 Per Month — Compound Growth ProjectionCalculate how £200 monthly contributions grow with compound interest over 10, 20, or 30 years. Free visual calculator.Invest £300 Per Month — How Much Will It Grow?See how £300 monthly investments compound over 10, 20, or 30 years. Visual calculator with insights and year-by-year projections.Invest £500 Per Month — Long-Term Growth CalculatorSee how £500 monthly investments compound over time. Visualise your potential returns with charts and year-by-year breakdown.Invest £750 Per Month — Wealth Projection CalculatorCalculate how £750 per month compounds over time. See projected balances, interest earned, and milestone years.Invest £1,000 Per Month — Wealth Building CalculatorCalculate how investing £1,000 per month compounds over time. See projected balances, interest earned, and growth charts.Invest £1,500 Per Month — High-Earner Growth CalculatorSee how investing £1,500 monthly builds wealth over time. Projections for 10, 20, and 30-year horizons with compound interest.Invest £2,000 Per Month — Accelerated Wealth CalculatorCalculate how £2,000 monthly investments compound into serious wealth. See projections with charts, milestones, and breakdowns.

Compound interest for UK investors

UK investors benefit from tax-efficient wrappers like the stocks & shares ISA, where all growth is completely tax-free. The annual ISA allowance for 2025/26 is £20,000 — that's up to £1,666 per month. If you maximise your ISA contributions and invest in a diversified portfolio returning 6–8% annually, compound interest can turn consistent saving into significant long-term wealth.

ISA vs general investment account

In a stocks & shares ISA, you pay no capital gains tax and no tax on dividends. In a general investment account (GIA), you'll pay CGT on gains above £3,000 and income tax on dividends above £500. For most UK investors, maximising your ISA before using a GIA makes the most sense. This calculator shows pre-tax growth, which matches ISA returns exactly.

What returns can UK investors expect?

A globally diversified index fund has historically returned around 7–10% per year before inflation. UK-focused funds may differ slightly. Cash ISAs currently offer 4–5% but historically lag equity returns over longer periods. Use the rate slider above to model different assumptions and find what works for your timeline.

UK Compound InterestCalculator (2026)