ISA Calculator UK 2025/26
Free ISA UK 2025/26 - Lifetime ISA, Cash ISA | UK Calc calculator for the UK. Get instant, accurate results with our easy-to-use online tool. Updated for...
Last updated: February 2026
UK ISA Calculator 2025/26
Calculate tax-free savings growth across Cash ISA, Stocks & Shares ISA, and Lifetime ISA
ISA Types & Allowances 2025/26
Annual ISA Allowance
£9,000 annual allowance for Junior ISAs
Types of ISA Available
| ISA Type | Best For | Key Features | Risk Level |
|---|---|---|---|
| Cash ISA | Safe savings | Fixed/variable interest, instant access options | Low |
| Stocks & Shares ISA | Long-term growth | Invest in shares, funds, bonds | Medium-High |
| Lifetime ISA | First home or retirement | 25% government bonus, max £4,000/year | Low-Medium |
| Innovative Finance ISA | P2P lending | Higher returns, peer-to-peer loans | High |
| Junior ISA | Children's savings | For under 18s, £9,000 limit | Low-Medium |
Lifetime ISA (LISA) Rules
- Age 18-39 to open, contribute until 50
- 25% government bonus (max £1,000/year)
- Max £4,000 annual contribution
- Use for first home (£450,000 max) or age 60+ retirement
- 25% penalty for other withdrawals
ISA Transfer Rules
- You can transfer ISAs between providers
- Transfers don't count toward annual allowance
- Must transfer entire current year contributions
- Can partial transfer previous years' ISAs
- Always use official transfer process, don't withdraw
Best ISA Rates (Updated Monthly)
| ISA Type | Top Rate | Provider Example | Access |
|---|---|---|---|
| Easy Access Cash ISA | 4.5% - 5.2% | Various | Instant |
| 1 Year Fixed Cash ISA | 5.0% - 5.5% | Various | Fixed 1 year |
| 2 Year Fixed Cash ISA | 4.8% - 5.3% | Various | Fixed 2 years |
| Stocks & Shares ISA | 7% - 10% avg* | Investment platforms | Variable |
Tax Benefits of ISAs
- Income tax on interest (Cash ISA)
- Dividend tax (Stocks & Shares ISA)
- Capital gains tax (Stocks & Shares ISA)
- No need to declare on tax returns
Frequently Asked Questions
How many ISAs can I open per year?
You can open one of each type of ISA per tax year, but your total contributions cannot exceed £20,000 (or £4,000 for Lifetime ISA which counts toward the £20,000).
Can I withdraw from my ISA?
Yes, from flexible ISAs you can withdraw and replace money in the same tax year. Fixed-term ISAs have penalties for early withdrawal. Lifetime ISAs have a 25% penalty except for first home or age 60+.
What happens to my ISA if I die?
Your spouse/civil partner can inherit your ISA allowance as an 'Additional Permitted Subscription' (APS), keeping the tax-free status.
Is my money protected in an ISA?
Cash ISAs are protected up to £85,000 per person per institution by the FSCS. Stocks & Shares ISAs are protected up to £85,000 for cash and £50,000 for investments.
7 Smart UK ISA Strategies (Save £2,000-£100,000+ Over 20 Years)
Always Use Your Full £20,000 ISA Allowance (Gain £100,000+ Tax-Free Over 20 Years)
How it works: £20,000 annual ISA allowance resets every 6 April. Any unused allowance is lost forever - you cannot carry it forward to future years. Over 20-30 years, unused allowances compound into massive lost tax savings.
Example: Max out Stocks & Shares ISA at £20,000/year for 20 years at 7% average return. Total contributions: £400,000. Future value: £819,309 tax-free! Same investment outside ISA (40% taxpayer): Growth taxed via dividend tax + CGT = approximately £50,000-£70,000 tax bill. Using ISA saves £50K-£70K!
Unused allowance cost: Miss £5,000 allowance this year at 7% growth over 20 years = £19,348 tax-free growth lost. Miss £10,000 = £38,697 lost. Always prioritize maxing ISA allowance before taxable savings!
Use Lifetime ISA for First Home (Get £32,000 Government Bonus + Tax-Free Growth)
How it works: Lifetime ISA (LISA): 25% government bonus on contributions up to £4,000/year (max £1,000 bonus/year). Age 18-39 to open, contribute until 50. Use for first home purchase (up to £450,000) or retirement at 60+. Bonus paid into ISA monthly.
Example: Age 25, buy first home at 33 (8 years). Contribute £4,000/year into LISA. Your contributions: £32,000. Government bonus: £8,000 (25% × £32,000). Growth at 5%/year cash LISA: £5,874. Total for first home: £45,874 vs £37,874 in regular savings = £8,000 free money!
LISA vs Help to Buy ISA: Help to Buy ISA closed to new accounts (Dec 2019). LISA better: £4,000/year vs £2,400/year, 25% bonus on full amount vs 25% on first £12,000 only. If opened Help to Buy ISA before 2019, can transfer to LISA.
Choose Stocks & Shares ISA for Long-Term Wealth (7-10% Returns vs 4-5% Cash ISA)
How it works: Stocks & Shares ISA invests in shares, funds, ETFs, bonds. Historically: 7-10% average annual returns over 10+ years (not guaranteed, can fall short-term). Cash ISA: 4-5% fixed (2025/26 rates). Over 20-30 years, compound growth difference is massive.
Example: £20,000/year for 20 years. Cash ISA at 4.5%: total = £619,964. Stocks & Shares ISA at 7%: total = £819,309. Difference: £199,345 more! S&S ISA vs taxable investment account (40% taxpayer paying dividend tax + CGT): saves additional £50K-£70K in tax.
Risk vs reward: Cash ISA = guaranteed but low growth (inflation erosion risk). S&S ISA = volatility but higher long-term returns. Time horizon 10+ years = S&S ISA historically better. 0-5 years = Cash ISA safer. Split strategy: Cash ISA for emergency fund (6 months expenses), S&S ISA for long-term goals (retirement, 10+ years).
Transfer Old ISAs to Better Providers (Increase Returns by 1-2%/Year = £20,000+ Over 20 Years)
How it works: ISA transfers move existing ISAs between providers without losing tax-free status. Transfers do NOT count toward annual £20,000 allowance. Must use official ISA transfer process - never withdraw and redeposit (loses tax-free status). Can transfer previous years' ISAs in full or part, must transfer current year ISA in full.
Example: £50,000 in old Cash ISA at 2% interest = £1,000/year. Transfer to best Cash ISA at 5% = £2,500/year. Gain: £1,500/year extra! Over 20 years at 5%: original strategy = £132,664, transfer strategy = £165,329. Transfer gains £32,665 more!
When to transfer: Cash ISA rate below market leaders (compare MoneySavingExpert, Moneyfacts). S&S ISA platform fees high (0.5%+ annual fee vs 0.15-0.25% low-cost platforms like Vanguard, Fidelity, AJ Bell). Want different investment options (current provider limited fund selection).
Use ISA Allowance Splitting Strategy (Optimize Cash + Growth Balance)
How it works: You can open one of each ISA type per tax year and split £20,000 allowance across multiple ISAs. Example: £4,000 to LISA (get £1,000 bonus) + £10,000 to S&S ISA (long-term growth) + £6,000 to Cash ISA (emergency fund). Maximizes flexibility and tax efficiency.
Example age 28, first-time buyer target age 33: LISA: £4,000/year (£1,000 bonus, save for home deposit). S&S ISA: £10,000/year (long-term retirement 30+ years, 7% growth). Cash ISA: £6,000/year (emergency fund 6-12 months expenses, instant access). After 5 years: LISA = £27,500 (deposit ready), S&S ISA = £57,500 (growing), Cash ISA = £34,500 (accessible). Total: £119,500 all tax-free!
£4,000/year
25% bonus = £1,000
First home deposit
£10,000/year
7% growth
Retirement (30+ years)
£6,000/year
4.5% interest
Emergency fund
Bed & ISA Strategy (Move Shares from Taxable Account to ISA Tax-Free Wrapper)
How it works: "Bed & ISA" = sell shares in taxable account, immediately buy same shares inside ISA wrapper using ISA allowance. Moves existing investments into tax-free protection. Future dividends + capital gains now tax-free. May trigger CGT on sale (but use £3,000 annual CGT allowance to minimize). Offered by most investment platforms as single transaction.
Example: £40,000 shares in taxable account, bought years ago at £30,000 (£10,000 gain). Sell all, trigger £10,000 gain - £3,000 CGT allowance = £7,000 taxable gain × 20% CGT = £1,400 CGT bill. Rebuy £40,000 inside ISA wrapper using ISA allowance. Future growth now tax-free. If held 20 years outside ISA, grows to £154,892 at 7%, dividend tax + CGT on £114,892 growth (40% taxpayer) ≈ £30,000-£40,000 tax. Bed & ISA saves £30K-£40K, costs £1,400 upfront. Net saving: £28,600-£38,600!
When to use: Large taxable investment account (£50K+). Unused ISA allowance available. Portfolio grown significantly (future tax liability will be substantial). Maximize CGT annual allowance (£3,000 2025/26) to minimize upfront tax on transfer.
Use Spousal ISA Strategy (Equalize Wealth + Minimize Future Tax)
How it works: Each person gets separate £20,000 ISA allowance (couples = £40,000/year total). If one spouse earns more, they can gift money to other spouse to use their ISA allowance. No gift tax between spouses. Equalizes wealth, minimizes tax on non-ISA assets, protects more money in tax-free wrappers.
Example couple, combined savings £40,000/year: High earner maxes their £20,000 ISA, gifts £20,000 to spouse for their ISA. Total: £40,000/year into ISAs! Over 20 years at 7%: ISA total = £1,638,618 all tax-free. If only one ISA used (£20,000/year): ISA total = £819,309, other £400,000 in taxable accounts taxed ≈ £50K-£70K. Spousal strategy saves £50K-£70K in tax!
Additional benefit: On death, surviving spouse can inherit ISA as "Additional Permitted Subscription" (APS) on top of their own allowance, maintaining tax-free status. Equalizing ISA wealth provides more inheritance protection.
7 Costly UK ISA Mistakes (Lose £2,000-£100,000+)
Not Using Your £20,000 Annual ISA Allowance (Lose £50,000-£100,000+ Over 20 Years)
The mistake: Leaving unused ISA allowance each year. "I'll max it out next year" or "I don't have the full £20,000 so I won't bother". Unused allowance is lost forever on 6 April - cannot carry forward.
The cost: Miss £10,000 allowance each year for 20 years. If invested in S&S ISA at 7%, that's £10,000/year × 20 years = £200,000 contributions, grows to £409,654 tax-free. Instead sits in taxable account: tax bill (40% taxpayer) ≈ £30,000-£40,000. Total loss: £30K-£40K in unnecessary tax!
The fix: Use whatever ISA allowance you can afford, even £50/month (£600/year). £600/year for 30 years at 7% = £56,641 tax-free vs £46,700 taxable (20% taxpayer) = £2,000 saved. Every £ in ISA is £ protected from tax forever. Start small, increase as income grows.
Choosing Wrong ISA Type (Cash ISA vs S&S ISA = £200,000+ Difference Over 20 Years)
The mistake: Using Cash ISA for long-term goals (10+ years). "Shares are risky, I'll stick to safe Cash ISA". Inflation erodes cash value over time. 4% cash vs 7% stocks over 20+ years = massive lost growth.
The cost: £20,000/year for 20 years. Cash ISA at 4.5%: total = £619,964. Stocks & Shares ISA at 7% (historical average): total = £819,309. Difference: £199,345 lost! Cash ISA "safe" but opportunity cost is huge over decades.
The fix: Match ISA type to timeline. 0-3 years (house deposit, car, wedding) = Cash ISA (guaranteed). 5-10 years (moderate goals) = mix Cash + S&S ISA. 10+ years (retirement, long-term wealth) = Stocks & Shares ISA (time smooths volatility). Don't fear stock market for long-term - historically beats cash every 10+ year period since 1900.
Exceeding £20,000 Annual ISA Allowance (HMRC 1% Penalty + Lose Tax Benefits)
The mistake: Contributing more than £20,000 across all ISAs in one tax year (6 April - 5 April). Opening multiple Cash ISAs in same year (allowed one of each type only). Not tracking contributions across providers.
The cost: HMRC charges 1% penalty on excess ISA contributions. Excess amount loses tax-free status (taxed as normal savings). Example: contribute £25,000 (£5,000 over). Penalty: £5,000 × 1% = £50. Plus £5,000 taxed as normal savings going forward, not ISA-protected. Total cost: £50 penalty + lost tax benefits on £5,000!
The fix: Track all ISA contributions carefully (spreadsheet or ISA provider dashboard). Remember tax year = 6 April to 5 April (not calendar year!). LISA counts toward £20,000 total (max £4,000 to LISA + £16,000 to other ISAs). If exceed, notify HMRC immediately to minimize penalty - they may allow correction if caught early.
Withdrawing Instead of Transferring ISA (Lose Tax-Free Status Forever)
The mistake: Want to move ISA to better provider. Withdraw money from old ISA, deposit into new ISA. Seems logical but wrong! Withdrawing ISA and redepositing = loses tax-free wrapper. Counts toward new annual allowance.
The cost: Example: £50,000 in old ISA, built over 5 years. Withdraw and deposit into new ISA. Problem: £50,000 exceeds £20,000 annual allowance. Only £20,000 can go into new ISA this year, £30,000 loses ISA protection forever! That £30,000 now taxable. Future growth taxed at 20-45% (dividend tax + CGT). Over 20 years at 7%, that £30,000 grows to £116,184 - tax bill ≈ £15,000-£25,000. Total loss: £15K-£25K in unnecessary tax!
The fix: ALWAYS use official ISA transfer process. Contact new provider, request ISA transfer (not withdrawal). They handle transfer directly with old provider. Transfer does NOT count toward annual £20,000 allowance. Can transfer £500,000 ISA and still contribute new £20,000 same year. Transfer takes 15-30 days typically.
Paying High ISA Platform Fees (1% Annual Fee = £20,000-£50,000 Lost Over 20 Years)
The mistake: Using expensive ISA platform without comparing fees. "All ISA providers are the same". Platform fees range 0.15%-1%+ annually. Over decades, fee difference compounds into massive losses.
The cost: £20,000/year for 20 years, 7% gross returns. High-fee platform (1% annual fee): net return = 6%, total = £734,884. Low-fee platform (0.25% annual fee): net return = 6.75%, total = £791,780. Fee difference costs £56,896! Just 0.75% fee difference = £57K lost!
The fix: Compare ISA platform fees annually. Low-cost leaders (2025/26): Vanguard (0.15%), Fidelity (0%), AJ Bell (0.25%), Interactive Investor (flat £9.99/month, better for large portfolios £100K+). Consider fund fees too (total cost = platform fee + fund OCF). Transfer ISA to cheaper provider using official transfer process (not withdrawal). Every 0.1% saved = thousands more in pocket over 20-30 years.
Ignoring Lifetime ISA 25% Government Bonus (Lose £8,000-£32,000 Free Money)
The mistake: Eligible for Lifetime ISA (age 18-39, saving for first home or retirement) but use regular ISA instead. "LISA rules are complicated, I'll skip it". Leaving £1,000/year free government money on table.
The cost: Age 25-32 (8 years until first home purchase). Could contribute £4,000/year to LISA, get £1,000 bonus/year = £8,000 free over 8 years. Instead contribute £4,000/year to regular S&S ISA (no bonus). First home deposit: LISA = £45,874 (with bonus + growth), regular ISA = £37,874. Miss £8,000 free government money! Or contribute £4,000/year age 18-50 (32 years), total bonus = £32,000. Not using LISA = lose £32,000 free!
The fix: If age 18-39 AND (buying first home OR saving for retirement): open LISA immediately! LISA bonus is free money - too good to miss. Contribute £4,000/year (£333/month) to LISA first, then use remaining £16,000 allowance for other ISAs. Aware of 25% withdrawal penalty (only for non-home, non-retirement withdrawals) - but if committed to first home or retirement goal, penalty won't apply. Open LISA even if only contributing £50/month - 25% bonus = instant 25% return!
Not Declaring ISAs on Tax Return When Required (Penalties + HMRC Investigation)
The mistake: ISA gains are tax-free and usually don't need declaring on tax return. BUT must declare if: exceeded ISA allowance, invalid ISA (e.g. contributed while non-UK resident), HMRC specifically requests. Some think "tax-free = never declare" which can trigger penalties.
The cost: HMRC discovers unreported invalid ISA contributions or excess allowance. Late declaration penalties: £100 initial + £10/day after 3 months + up to 100% of tax owed if deliberate. Investigation costs time + stress. Interest charged on unpaid tax backdated. Example: £10,000 invalid ISA, should have paid £2,000 tax (20% growth × 40% rate), undeclared 2 years. Penalty: £100 + £2,000 tax + interest ≈ £200 = £2,300 total!
The fix: Declare ISAs on tax return if: exceeded annual allowance, contributed while non-UK tax resident, void ISA (e.g. junior ISA after age 18 before converting to adult ISA). Most valid ISAs don't need declaring. If unsure, declare anyway (penalty-free if declared voluntarily). Keep ISA contribution records for 5+ years in case HMRC queries. If discover mistake, notify HMRC immediately using "error correction" process - lower penalties than if HMRC discovers first.
Official UK ISA Resources & Support
HMRC ISA Rules & Guidance
Official ISA rules, allowances, tax benefits, eligibility. Updated for 2025/26 tax year. Essential reading before opening ISA.
View GOV.UK ISA Guide →Lifetime ISA Official Rules
LISA 25% bonus, first home purchase rules (£450K limit), retirement withdrawal (age 60+), early withdrawal 25% penalty details.
View LISA Guide →Compare Best ISA Rates
MoneySavingExpert ISA comparison tables. Best Cash ISA rates (easy access, fixed), S&S ISA platform fees. Updated weekly.
Compare ISA Rates →S&S ISA Platform Comparison
Compare Stocks & Shares ISA platforms. Fees (0.15%-1%+), fund selection, ease of use. Monevator annual platform comparison.
Compare Platforms →FSCS ISA Protection
Financial Services Compensation Scheme. ISA protection limits: £85,000 cash per institution, £85,000 + £50,000 investments. What's covered.
Check FSCS Protection →HMRC ISA Helpline
ISA queries: allowances, eligibility, transfers, void ISAs. Phone: 0300 200 3300. Mon-Fri 8am-6pm. Online query form available.
Contact HMRC ISA Team →📚 Read Our Comprehensive Guide
Learn more tips, tricks, and detailed explanations to get the most out of this calculator.
Read the Guide →Related UK Financial Calculators
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Calculate monthly payments, affordability. Use Lifetime ISA for first home deposit (get 25% bonus up to £450K property).
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Written by UK Tax & ISA Specialists
Our team of chartered accountants and financial advisors provide expert UK ISA guidance based on current HMRC rules (2025/26 tax year). All calculations independently verified for accuracy. We prioritize evidence-based ISA strategies using official government data, helping UK taxpayers maximize tax-free savings and minimize tax liabilities through proper ISA planning.
Last updated: 14 February 2026 | Verified against GOV.UK ISA rules and HMRC guidance
Expert Reviewed — This calculator is reviewed by our team of financial experts and updated regularly with the latest UK tax rates and regulations. Last verified: February 2026.
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Official Sources
How to Use This ISA Calculator
- Enter your initial lump sum — If you have a lump sum to deposit into your ISA, enter the amount. Leave as £0 if you plan to contribute monthly only.
- Set your monthly contribution amount — Enter how much you plan to add each month. Regular contributions benefit from pound-cost averaging and steady compound growth.
- Choose your expected annual growth rate — Select a realistic rate based on your ISA type: Cash ISAs typically offer 3–5%, while Stocks & Shares ISAs have historically averaged 5–8% over the long term.
- Set your investment period in years — Choose how long you plan to hold your ISA. Longer time horizons allow compound interest to work harder for your money.
- View your projected ISA value with tax-free growth — The calculator shows your estimated ISA balance, total contributions, and interest earned. It also compares your tax-free ISA returns against a taxable savings account so you can see exactly how much you save by using your ISA allowance.
Worked Examples: ISA Growth Projections
Example 1: Cash ISA — Lump Sum Deposit
Scenario: You deposit a £20,000 lump sum into a Cash ISA earning 4.5% interest for 5 years.
Projected value: £24,931 — all interest earned is completely tax-free.
A basic rate taxpayer (20%) would pay approximately £985 in tax on the same interest in a regular savings account outside an ISA.
Example 2: Stocks & Shares ISA — Monthly Contributions
Scenario: You invest £500 per month into a Stocks & Shares ISA with 7% annual growth for 10 years.
Total contributions: £60,000 | Projected value: £86,500
Your tax-free gains of £26,500 would otherwise be subject to Capital Gains Tax or dividend tax in a standard investment account.
Example 3: Lifetime ISA — With Government Bonus
Scenario: Aged 18–39, you contribute the maximum £4,000 per year to a Lifetime ISA at 6% growth for 10 years. The government adds a 25% bonus (£1,000/year).
Your contributions: £40,000 | Government bonus: £10,000 | Projected value: ~£72,400
The LISA bonus and all growth are tax-free when used for your first home (up to £450,000) or retirement after age 60.
Example 4: Maximum ISA Allowance — Long-Term Wealth
Scenario: You invest the full £20,000 ISA allowance each year at 6% annual growth for 20 years.
Total contributions: £400,000 | Projected value: £735,000+
All capital gains and dividends are entirely tax-free. At higher-rate tax, this could save you over £60,000 in CGT and dividend tax compared to a general investment account.
Sources & Methodology
Official Sources
2025/26 ISA Allowances
- Annual ISA allowance: £20,000
- Lifetime ISA (LISA): £4,000 (counts towards the £20,000 total)
- Junior ISA (JISA): £9,000
Compound Interest Formula
This calculator uses the standard compound interest formula with regular contributions:
FV = PV(1 + r)n + PMT × [(1 + r)n − 1] / r
Where: FV = Future Value, PV = Present Value (lump sum), r = periodic interest rate, n = number of periods, PMT = regular contribution amount.
Disclaimer: Projected returns are estimates based on the growth rate you enter and are not guaranteed. Past performance does not guarantee future results. Investment values can go down as well as up, and you may get back less than you invest. Tax treatment depends on individual circumstances and may change in future. This calculator is for illustrative purposes only and does not constitute financial advice.