Stocks and Shares ISA Calculator – Calculate ISA Growth & Returns

Your Stocks and Shares ISA is one of the few places where money can grow without any tax touching it. No income tax on dividends. No capital gains tax on profits. No tax on interest. This Stocks and Shares ISA Calculator shows what that tax-free growth could be worth over time. Enter a starting balance, a monthly contribution, and a growth assumption — and you’ll see the projected final value, split into what you put in and what compounding added.

What’s already in the account. Leave at 0 if you’re just starting.

How much you plan to add each month. This is your own planning assumption — not a check against your available ISA allowance. The overall annual ISA limit is £20,000 for 2026/27. There’s no separate monthly cap — the limit applies to your total deposits across the tax year.

Average yearly growth rate, net of fees. Pick a number that matches the portfolio you’re actually using.

How long you plan to keep the money invested. Most ISA providers recommend a minimum five-year horizon for stocks and shares.

Optional. If you plan to raise contributions over time — matching inflation, or ramping up as your income grows — enter the annual increase here. Leave at 0 for a flat contribution.

Final ISA Value
—
Total Contributed
—
Investment Growth
—
Growth Multiple
—
Projected ISA Value
—
Set your inputs to calculate
Detail Value

🔥 Popular Calculators

One thing to know before you trust the output. This Stocks and Shares ISA Calculator assumes contributions go in at the start of each month, that growth compounds monthly at a steady rate, and that no withdrawals happen during the projection. It uses a simplified model and doesn’t check whether your contributions fit inside your personal ISA allowance. Real markets don’t deliver smooth returns. ISA rules and limits change over time — the figures and rules referenced here (2026/27 allowances and the April 2027 cash ISA changes) were current at the time of publication, but you should always verify them against the latest GOV.UK or HMRC guidance before making any decisions.

💱 This calculator is built for UK Stocks and Shares ISAs and shows results in pounds sterling. If you’re modelling a similar tax-advantaged account in another country, the math still works — but the limits and rules won’t apply.

What Is a Stocks and Shares ISA Calculator?

A Stocks and Shares ISA Calculator tells you what your Individual Savings Account might grow into over the years you hold it. You hand it a starting balance, a monthly contribution, and a growth rate. It runs the numbers forward and slices the result in two: the money you paid in, and the growth the account produced on top.

What sets a Stocks and Shares ISA apart from most other investment accounts is the tax treatment. Dividends, interest, and capital gains earned inside an ISA are completely free of UK tax. No income tax on dividends. No capital gains tax on profits when you sell. No tax on interest. And you don’t have to report any of it on a tax return. Outside an ISA, dividends above the £500 dividend allowance may be subject to dividend income tax, investment gains may be subject to Capital Gains Tax, and interest may be subject to savings tax above the personal savings allowance. Inside an ISA, none of that applies.

How to Use This Stocks and Shares ISA Calculator

Five inputs, plus three preset buttons if you’d rather start from a common scenario.

Starting ISA Balance. What’s already in the account today. If you’ve never contributed, leave it at zero. If you’re revisiting an existing plan, enter the current market value — not the total you’ve contributed over the years. Growth and contributions both live inside the same balance.

Monthly Contribution. What you plan to add each month. This is a planning assumption you enter — the calculator doesn’t know your actual ISA allowance or whether you’ve used any of it already. The overall annual ISA limit is £20,000 for 2026/27. There’s no separate monthly cap — the limit applies to your total deposits across the tax year. Contributing a steady £1,667 a month would use up the allowance by year-end, but that’s just an arithmetic equivalent, not a rule. Check your own remaining allowance before acting on any specific figure.

Expected Annual Return. Your best guess at what the portfolio earns each year, after fund fees. A Stocks and Shares ISA can hold the same investments as a taxable account — funds, ETFs, individual shares, bonds, even some private investments. What you hold depends on your time horizon, risk tolerance, and how soon you’ll need the money. A conservative mix might target 4% to 5%. A balanced portfolio might aim for 6% to 8%. An equity-heavy one could target 9% or more, with more volatility along the way. These are projection assumptions, not guarantees, and actual returns can be higher, lower, or negative in any given year.

Years to Grow. How long you plan to leave the money invested. This single input changes the result the most. Double the years and you can more than double the final value, depending on the return rate. Most ISA providers recommend a minimum five-year horizon for stocks and shares, because shorter periods don’t give the market time to recover from downturns.

Annual Contribution Increase (%). Optional, and easy to overlook. If you plan to increase your contribution each year — matching inflation, or ramping up as your income grows — enter that percentage here. Leaving it at 0 keeps contributions flat, which is the default for most projections.

Hit calculate and you’ll see four numbers: the projected final value, the total money you put in, the growth the account generated, and a growth multiple (final value divided by total contributions). Below that, the table breaks down the value at intermediate milestones so you can see how the curve accelerates over time.

How Stocks and Shares ISA Growth Is Calculated

The math is compound growth applied month by month. Each month, your contribution goes in, and the whole balance grows at the monthly equivalent of the assumed annual rate.

Balancenext = (Balancecurrent + Contribution) × (1 + monthly rate)

The monthly rate comes from the annual figure using the standard compound interest formula:

Monthly Rate = (1 + Annual Rate)1/12 − 1

If you’ve entered a contribution growth rate, the monthly contribution itself rises each year before being added to the balance. Contributions and growth are tracked separately, so the final breakdown shows how much of your ending balance came from each source.

Here’s what that looks like in practice. Start with £0, contribute £500 a month for 20 years, and earn 7% annually. Your total contributions come to £120,000. With monthly compounding, the account grows to around £255,200 — meaning roughly £135,200 of that balance is investment growth, not your money.

Change one input and the picture shifts. Bump the return to 8% and the final value climbs by tens of thousands. Increase contributions 3% a year and the end result grows further. Cut the years from 20 down to 10 and the compounding effect shrinks dramatically — the earliest years do most of the heavy lifting.

The order in which contributions arrive matters too. Money put in early gets more months of compounding than money put in late, so a lump sum on day one outperforms an equal amount dribbled in over a decade. The calculator assumes contributions land at the start of each month, which is a reasonable approximation for someone contributing on a regular schedule.

ISA Contribution Allowances and Key Rules

The ISA allowance is the cap on how much you can add to your ISAs without triggering a tax charge. It resets every tax year, and understanding how it works helps you plan contributions without breaching the limit.

For the 2026/27 tax year (6 April 2026 to 5 April 2027), the overall adult ISA allowance is £20,000. You can split that £20,000 across different types of ISA — Cash ISA, Stocks and Shares ISA, Innovative Finance ISA, and Lifetime ISA — in whatever combination suits your goals. The allowance applies to total deposits across all your ISAs, not per account. If you put £15,000 into a Cash ISA, you have £5,000 left for a Stocks and Shares ISA that year.

Unused allowance doesn’t roll over. If you deposit £10,000 one year, you can’t deposit £30,000 the next to make up the difference. The allowance resets on 6 April, and the previous year’s unused portion is gone. That’s why the “use it or lose it” reminder comes up every March.

From 6 April 2027, the rules change for cash ISAs. Savers aged under 65 will only be able to deposit up to £12,000 of their £20,000 allowance into a Cash ISA, with the remaining £8,000 available for Stocks and Shares ISAs or other eligible ISAs. Those aged 65 or over are unaffected. The change only applies to new deposits from April 2027 — existing Cash ISA balances aren’t affected. You can read the full details in HMRC’s Tax-Free Savings Newsletter 19.

Junior ISAs have a separate allowance — £9,000 per child for the 2026/27 tax year. Lifetime ISAs have a lower contribution limit of £4,000 a year (which counts towards your overall £20,000), but the government adds a 25% bonus on top, up to £1,000 per year, for first-home purchases or retirement.

Generally, you must be aged 18 or over and UK resident to open an adult ISA, although certain exceptions apply to Crown servants, members of the armed forces, and their spouses or civil partners. Junior ISAs are available for children under 18. You can have multiple ISAs, subject to the current subscription rules and the overall annual allowance.

Stocks and Shares ISA vs Cash ISA

Both accounts are tax-free. What differs is what you’re holding inside them — and that difference drives the long-term outcome.

Cash ISA works like a savings account. Your money sits in cash, and you earn interest. The interest is tax-free, which makes Cash ISAs more attractive than ordinary savings accounts if you’re a higher-rate taxpayer or have exceeded your Personal Savings Allowance. But cash returns have historically lagged inflation over long periods, which erodes purchasing power even when the nominal balance doesn’t fall.

Stocks and Shares ISA invests your money in the market — funds, ETFs, individual shares, bonds. Your balance fluctuates daily, and you can lose money. But over long periods, shares have historically delivered higher returns than cash. Data from Unbiased shows the average annual return on stocks and shares ISAs over the last 10 years was 6.79%, compared with 1.79% for lower-risk cash ISAs. Over 20 or 30 years, that gap compounds into a significant difference.

The right choice depends on your time horizon and risk tolerance. Money you’ll need within five years probably belongs in cash, where the value won’t drop. Money you’re investing for retirement or another long-term goal can typically tolerate short-term volatility in exchange for higher expected returns. Many people use both — cash for near-term goals and an emergency buffer, stocks and shares for long-term growth.

One point worth keeping in mind: cash isn’t risk-free. Inflation can reduce what your money buys. If a Cash ISA pays 4% and inflation runs at 3%, your real return is only 1%. Over decades, that gap matters as much as the visible balance.

Worked Examples You Can Relate To

Three scenarios showing different savings patterns. All assume contributions go in at the start of each month and compound at a steady annual rate, with no withdrawals.

Example 1: The Steady Saver

Start with £0, contribute £500 a month for 20 years, and earn 7% annually.

  • Total contributions: £120,000
  • Investment growth: approximately £135,200
  • Projected final value: approximately £255,200
  • Growth multiple: 2.1×

Over 20 years, more than half the final balance ends up coming from investment growth rather than your own contributions. That’s compounding doing its job — and the reason starting early matters more than starting big.

Example 2: A Shorter Horizon

Start with £0, contribute £500 a month for 10 years, and earn 7% annually.

  • Total contributions: £60,000
  • Investment growth: approximately £26,000
  • Projected final value: approximately £86,000
  • Growth multiple: 1.4×

Shortening the horizon from 20 years to 10 reduces contributions by £60,000 — but the final value drops by over £165,000. That gap is the value of time in the market, and it’s why late starts hurt even when the monthly amount stays the same.

Example 3: Rising Contributions

Start with £0, contribute £500 a month in year one and increase the contribution by 3% every year for 20 years, earning 7% annually.

  • Total contributions: approximately £161,200
  • Investment growth: approximately £159,900
  • Projected final value: approximately £321,200
  • Growth multiple: 2.0×

Raising contributions gradually with income — even by just 3% a year — turns the same 20-year plan into a much larger pile. The growth multiple stays similar, but the absolute pound amounts get far bigger.

Common Stocks and Shares ISA Mistakes to Avoid

A few missteps come up over and over. Each one costs real money, and most are easy to prevent.

Exceeding the allowance. Deposits above £20,000 in a tax year aren’t protected by the ISA wrapper and may trigger a tax charge. This usually happens when people move money between providers and lose track of their total contributions, or when they open multiple ISAs and forget the total. Track your deposits, and if you’re close to the limit, double-check before contributing.

Investing money you’ll need soon. Stocks and shares ISAs are unsuitable for short-term goals. If the market drops 20% in the year you need the money, you could be forced to sell at a loss. Most providers recommend a minimum five-year horizon, and longer is usually better. Keep short-term savings in cash.

Not using the full allowance when you can. The £20,000 allowance resets every April, and unused portions don’t roll over. If you have spare cash and a long-term goal, using more of the allowance earlier gives compounding more time to work. Even if you can’t max it out, contributing what you can still helps.

Ignoring fees. Platform charges, fund ongoing costs, and trading fees all reduce your net return. A 0.5% annual fee difference might not sound like much, but over 20 years it can cost tens of thousands of pounds. Check both the platform fee and the fund fee before choosing where to invest.

Panic-selling during downturns. Markets fall regularly. Investors who sell during a crash lock in losses that a patient investor never experiences. The ISA wrapper encourages long-term holding precisely because the tax benefits are most powerful over decades. If volatility makes you uncomfortable, a more conservative portfolio allocation is a better fix than selling.

Forgetting about non-resident rules. If you leave the UK, your existing ISA continues to grow tax-free within the UK, but you can’t open a new ISA or contribute to an existing one while you’re a non-resident (with some exceptions for Crown servants and their spouses). You may also owe tax to your new country of residence on income earned inside the ISA. Worth checking with an accountant if you’re moving abroad.

If this Stocks and Shares ISA Calculator was useful, these related tools might round out your financial planning.

Additional Financial Resources

For the official ISA rules, current allowances, and details of the upcoming cash ISA changes, GOV.UK’s Individual Savings Accounts page is the authoritative source.

For plain-English guidance on choosing between Cash ISAs and Stocks and Shares ISAs, and how the tax wrapper works in practice, the MoneyHelper guide to ISAs from the Money and Pensions Service is a useful, non-commercial overview.

Frequently Asked Questions About Stocks and Shares ISAs

It’s a projection tool that estimates how much a Stocks and Shares ISA could be worth after a chosen number of years. You enter a starting balance, monthly contributions, a growth assumption, and a time horizon — and it shows the final value along with how much came from contributions versus investment growth.
The overall adult ISA allowance is £20,000 for the 2026/27 tax year. You can split that across Cash ISAs, Stocks and Shares ISAs, Innovative Finance ISAs, and Lifetime ISAs in any combination. Junior ISAs have a separate £9,000 allowance. From April 2027, savers under 65 will only be able to put £12,000 of their allowance into a Cash ISA, with the remaining £8,000 available for Stocks and Shares ISAs. Check GOV.UK for the current figures before contributing.
It depends on what’s inside the account and your time horizon. A conservative, bond-heavy mix might target 4% to 5% a year. A balanced portfolio of stocks and bonds might aim for 6% to 8%. An equity-heavy portfolio could target 9% or more, with more volatility. Whatever rate you use, treat it as an assumption, not a promise. Real returns vary year to year, sometimes sharply.
Yes. Dividends, interest, and capital gains earned inside a Stocks and Shares ISA are exempt from UK Income Tax and Capital Gains Tax. You don’t need to report them on a tax return. There’s one exception — hold US-listed dividend-paying shares inside an ISA and the US withholds 15% of the dividend at source, which you can’t reclaim. For that reason, some investors hold US dividend payers in a pension instead, where the withholding is exempt under the UK-US tax treaty.
Yes. There are no restrictions on when or why you can withdraw from a Stocks and Shares ISA, and you won’t owe tax on the withdrawal. If your ISA is a flexible ISA, money you withdraw can be replaced within the same tax year without counting towards your £20,000 allowance. Not all providers offer flexible ISAs, so check before opening. Withdrawals from a non-flexible ISA permanently reduce your allowance for that year.
It depends on your time horizon. Money you’ll need within five years usually belongs in a Cash ISA, where the value won’t drop. Money you’re investing for retirement or another long-term goal can typically tolerate short-term volatility in exchange for higher expected returns. Historically, stocks and shares have delivered significantly higher returns than cash over long periods. Many people use both.
Up to £20,000 per tax year across all your ISAs combined. The allowance resets on 6 April each year, and unused portions don’t roll over. You can split it however you like between Cash, Stocks and Shares, Innovative Finance, and Lifetime ISAs.
No. Selling investments inside a Stocks and Shares ISA doesn’t trigger capital gains tax, and you don’t need to declare anything to HMRC. This is one of the key advantages over a taxable investment account, where profits above the annual capital gains allowance are taxed at 18% (basic rate) or 24% (higher rate) for most assets.

⚠️ Disclaimer: The results from this Stocks and Shares ISA Calculator are hypothetical projections based on user-supplied assumptions and are for educational and informational purposes only. They should not be treated as financial, investment, or tax advice. The calculator assumes contributions are added at the start of each month, compounds growth at a steady rate, and does not model withdrawals, changes to ISA rules, or taxes in jurisdictions outside the UK. It uses a simplified model and does not verify contributions against your personal ISA allowance. Real investment returns vary and may be negative. The value of investments can go down as well as up, and you may get back less than you put in. Tax rules can change. Please consult a qualified financial advisor or check GOV.UK for guidance specific to your situation.