Cash ISA
Best 3 year fixed rate ISAs
19 Cash ISAs fixed for 3 years, ranked by rate alone. The rate stays the same for the whole term, whatever happens to Bank Rate. Each one is checked on the provider's own site, and the highest on 6 October 2026 paid 5.15% AER.
3 year fixes at a glance
- Highest rate
- 5.15% AER
- Castle Trust Bank
- £10,000 at that rate earns
- £1,626
- Over 3 years, tax-free
- Accounts compared
- 19
- Checked on 6 October 2026
- Highest easy access rate
- 4.86% AER
- Variable, so it can change
Best 3 year fixed rate ISAs
Checked 6 October 2026. Ranked by rate. Links marked "Ad" can earn us commission, which never changes the order. How we make money
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1. Castle Trust Bank
3 year Fixed Rate e-Cash ISA
5.15%
AER fixed
- Access
- 3 years fixed
- Minimum
- £1,000
- Transfers in
- Yes
- Flexible
- No
Details and provider information
- Withdrawals
- Full-amount withdrawals before maturity (including transfer out) cost an early exit charge of 270 days' interest; ask by phone or secure message.
- How to open
- Online
- Your money is held by
- Castle Trust Capital plc
- Good to know
- Online only; needs a UK current account in your name. 14-day funding window, then no more deposits.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- Legal name
- Castle Trust Capital plc (trading as Castle Trust Bank)
- Country of incorporation
- England and Wales
- Principal place of business
- London, UK (registered office: 10 Norwich Street, London EC4A 1BD)
- Regulatory status
- Castle Trust Capital plc is authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority, under reference number 541910. Incorporated in England and Wales, company number 07454474 (FRN 541910)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence
- Complaints
- Financial Ombudsman Service
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2. West Brom Building Society
3 Year Fixed Rate ISA
5.10%
AER fixed
- Access
- Fixed to Oct 2029
- Minimum
- None
- Transfers in
- Yes
- Flexible
- No
Details and provider information
- Withdrawals
- You can withdraw or close early, but it costs 240 days' interest. Money taken out cannot be paid back in.
- How to open
- Online, Branch
- Your money is held by
- West Bromwich Building Society
- Good to know
- Matures on a set date, 31 October 2029. Interest is paid yearly, or monthly at 4.98% tax-free.
- Rate checked
- On the provider's own site on 6 October 2026. Source
- Legal name
- West Bromwich Building Society
- Country of incorporation
- United Kingdom
- Principal place of business
- West Bromwich, West Midlands, UK (head office: 2 Providence Place, West Bromwich B70 8AF)
- Regulatory status
- Authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority. Register No: 104877 (FRN 104877)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence
- Complaints
- Financial Ombudsman Service
-
3. Kent Reliance
Three Year Fixed Rate Cash ISA (Issue 6)
5.06%
AER fixed
- Access
- 3 years fixed
- Minimum
- £1,000
- Transfers in
- Yes
- Flexible
- Yes
Details and provider information
- Withdrawals
- Taking money out or transferring out costs a loss of interest (the days are in the key features shown when you apply), and you cannot add money after the first 30 days.
- How to open
- Online
- Your money is held by
- OneSavings Bank plc
- Good to know
- Fund it within 30 days of opening. Interest paid annually or monthly (4.95% gross monthly, same 5.06% AER). Balance must stay at £1,000 or more.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- More from Kent Reliance
- All Kent Reliance Cash ISAs compared
- Legal name
- OneSavings Bank plc (trading as Kent Reliance)
- Country of incorporation
- England and Wales
- Principal place of business
- Chatham, Kent, UK
- Regulatory status
- Authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority (FRN 530504)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence
- Complaints
- Financial Ombudsman Service
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4. United Trust Bank
Cash ISA 3 Year Bond
5.05%
AER fixed
- Access
- 3 years fixed
- Minimum
- £5,000
- Transfers in
- Yes
- Flexible
- No
Details and provider information
- Withdrawals
- Early withdrawal or transfer out is allowed but charged: 90 days' interest with under a year left, rising to 365 days' with 4 or more years left.
- How to open
- Online
- Your money is held by
- United Trust Bank Limited
- Good to know
- Online only, for UK-resident adults. Needs a nominated UK bank account in your own name; fund within 14 days of applying.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- Legal name
- United Trust Bank Limited
- Country of incorporation
- England and Wales
- Principal place of business
- London, UK (One Ropemaker Street, London EC2Y 9AW)
- Regulatory status
- Authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority (Firm Reference Number 204463). Registered in England and Wales 549690 (FRN 204463)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence
- Complaints
- Financial Ombudsman Service
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5. Charter Savings Bank
3 Year Fixed Rate Cash ISA
5.01%
AER fixed
- Access
- 3 years fixed
- Minimum
- £5,000
- Transfers in
- Yes
- Flexible
- No
Details and provider information
- Withdrawals
- Early access costs a charge equal to 270 days' interest on the amount withdrawn.
- How to open
- Online
- Your money is held by
- Charter Court Financial Services Limited
- Rate checked
- On the provider's own site on 30 October 2026. Source
- Legal name
- Charter Court Financial Services Limited (trading as Charter Savings Bank)
- Country of incorporation
- England and Wales
- Principal place of business
- Wolverhampton, UK
- Regulatory status
- Authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority (FRN 494549)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence
- Complaints
- Financial Ombudsman Service
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6. Vida Savings
3 Year Fixed Rate ISA
4.95%
AER fixed
- Access
- 3 years fixed
- Minimum
- £1,000
- Transfers in
- Yes
- Flexible
- Yes
Details and provider information
- Withdrawals
- Withdrawals and transfers out before the end of the term cost 270 days' interest. Flexible ISA: money withdrawn can be replaced in the same tax year.
- How to open
- Online
- Your money is held by
- Vida Bank Limited
- Good to know
- Online only (website or app); needs a UK bank account in your name. Deposits accepted for the first 21 days only.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- Legal name
- Vida Bank Limited (trading as Vida Savings)
- Country of incorporation
- England and Wales
- Principal place of business
- London, UK (registered office: 1 Battle Bridge Lane, London SE1 2HP)
- Regulatory status
- Vida Bank, Vida Savings and Vida Homeloans are trading names of Vida Bank Limited, registered in England and Wales with company number 09837692. Authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and Prudential Regulation Authority, Financial Services Register Firm Reference Number 738741 (FRN 738741)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence
- Complaints
- Financial Ombudsman Service
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7. Nationwide Building Society
3 Year Fixed Rate Cash ISA
4.90%
AER fixed
- Access
- 3 years fixed
- Minimum
- None
- Transfers in
- Yes
- Flexible
- No
Details and provider information
- Withdrawals
- You can only close the whole ISA early, with a charge of 180 days' interest, and there are no part withdrawals or top-ups.
- How to open
- Branch (new customers), online or app (existing customers)
- Your money is held by
- Nationwide Building Society
- Good to know
- New customers must apply in branch. Fund it when you open it. Moves to an instant access Cash ISA at the end of the term.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- More from Nationwide
- All Nationwide Cash ISAs compared
- Legal name
- Nationwide Building Society
- Country of incorporation
- United Kingdom
- Principal place of business
- Swindon, UK
- Regulatory status
- Authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority (FRN 106078)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence, shared with Virgin Money
- Complaints
- Financial Ombudsman Service
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8. Skipton Building Society
3 Year Fixed Rate Cash ISA
4.87%
AER fixed
- Access
- 3 years fixed
- Minimum
- None
- Transfers in
- Yes
- Flexible
- No
Details and provider information
- Withdrawals
- No part withdrawals, but you can close the account and take the full balance at any time for a charge of 240 days' interest after the 14-day cancellation period.
- How to open
- Online, app, branch, phone or post
- Your money is held by
- Skipton Building Society
- Good to know
- Closes to payments in and ISA transfers on 11 November 2026. Interest annual or monthly at the same AER. Maximum balance £1 million. No joint accounts.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- More from Skipton
- All Skipton Cash ISAs compared
- Legal name
- Skipton Building Society
- Country of incorporation
- United Kingdom
- Principal place of business
- Skipton, North Yorkshire, UK
- Regulatory status
- Authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority (FRN 153706)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence
- Complaints
- Financial Ombudsman Service
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9. Santander
3 Year Fixed Rate ISA
4.85%
AER fixed
- Access
- Fixed to Nov 2029
- Minimum
- £500
- Transfers in
- Yes
- Flexible
- No
Details and provider information
- Withdrawals
- Take out all of the balance, not part, by closing the account or transferring the ISA, for a charge of 120 days' interest.
- How to open
- Online, app or branch
- Your money is held by
- Santander UK plc
- Good to know
- Fixed until 1 November 2029. Deposits close on 30 November 2026. £200 hotel voucher for a full transfer of £25,000 or more from a non-Santander ISA.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- More from Santander
- All Santander Cash ISAs compared
- Legal name
- Santander UK plc
- Country of incorporation
- England and Wales
- Principal place of business
- London, UK
- Regulatory status
- Authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority (FRN 106054)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence
- Complaints
- Financial Ombudsman Service
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10. Hampshire Trust Bank
3 Year Online ISA Fixed Saver (Issue 11)
4.83%
AER fixed
- Access
- 3 years fixed
- Minimum
- None
- Transfers in
- Yes
- Flexible
- No
Details and provider information
- Withdrawals
- You can withdraw or transfer out your full balance early for a fee of 90 days' interest for each year (or part year) remaining. No partial transfers.
- How to open
- Online
- Your money is held by
- Hampshire Trust Bank Plc
- Good to know
- Online only, for UK permanent residents aged 18 or over. Fund within 14 days of applying; start any ISA transfer within 14 days of opening.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- Legal name
- Hampshire Trust Bank Plc
- Country of incorporation
- England and Wales
- Principal place of business
- London, UK (registered office: 80 Fenchurch Street, London EC3M 4BY)
- Regulatory status
- Authorised by the Prudential Regulation Authority and regulated by the Prudential Regulation Authority and the Financial Conduct Authority (FRN 204601). Company registered in England and Wales, registration number 01311315 (FRN 204601)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence
- Complaints
- Financial Ombudsman Service
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11. Barclays
Premier Triple Access 3-Year Flexible Cash ISA (Issue 4)
4.81%
AER fixed
- Access
- 3 years fixed
- Minimum
- None
- Transfers in
- Yes
- Flexible
- Yes
Details and provider information
- Withdrawals
- Three withdrawals allowed during the term, each up to 10% of the balance at the time. Closing or transferring out early costs 270 days' interest.
- How to open
- App, online banking, branch or phone
- Your money is held by
- Barclays Bank UK PLC
- Good to know
- For Barclays Premier customers only. A transfer reward of up to £600 for moving in £10,000 or more from another provider by 25 November 2026.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- More from Barclays
- All Barclays Cash ISAs compared
- Legal name
- Barclays Bank UK PLC
- Country of incorporation
- England
- Principal place of business
- London, UK
- Regulatory status
- Authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority (FRN 759676)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence, shared with Tesco Bank
- Complaints
- Financial Ombudsman Service
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12. Hodge Bank
3 Year Fixed Rate Cash ISA
4.81%
AER fixed
- Access
- 3 years fixed
- Minimum
- £1,000
- Transfers in
- No
- Flexible
- No
Details and provider information
- Withdrawals
- Early access costs a charge equal to 270 days' interest on the amount withdrawn.
- How to open
- Online
- Your money is held by
- Julian Hodge Bank Limited
- Rate checked
- On the provider's own site on 30 October 2026. Source
- Legal name
- Julian Hodge Bank Limited (trading as Hodge Bank)
- Country of incorporation
- England and Wales
- Principal place of business
- Cardiff, UK
- Regulatory status
- Authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority (FRN 204439)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence
- Complaints
- Financial Ombudsman Service
-
13. TSB
Fixed Rate Cash ISA (3 year term)
4.75%
AER fixed
- Access
- 3 years fixed
- Minimum
- None
- Transfers in
- Yes
- Flexible
- Yes
Details and provider information
- Withdrawals
- Withdrawals are allowed after 14 days but cost 270 days' interest on the amount taken out or transferred.
- How to open
- App (existing customers), online or branch
- Your money is held by
- TSB Bank plc
- Good to know
- All deposits and transfers must arrive within 30 days of opening. Matures into a Cash ISA Saver without the bonus.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- More from TSB
- All TSB Cash ISAs compared
- Legal name
- TSB Bank plc
- Country of incorporation
- Scotland
- Principal place of business
- Edinburgh, UK
- Regulatory status
- Authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority (FRN 191240)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence
- Complaints
- Financial Ombudsman Service
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14. Zopa
Smart ISA (3 Year Fixed Term pot)
4.65%
AER fixed
- Access
- 3 years fixed
- Minimum
- None
- Transfers in
- Yes
- Flexible
- No
Details and provider information
- Withdrawals
- Early access before the term ends closes the fixed term pot and costs 270 days of interest.
- How to open
- App
- Your money is held by
- Zopa Bank Limited
- Good to know
- Open in the Zopa app via a Smart Saver account. Add money in the first 30 days; transfers in start at £500. Interest paid monthly. Moves to an Access ISA pot at the end.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- More from Zopa
- All Zopa Cash ISAs compared
- Legal name
- Zopa Bank Limited
- Country of incorporation
- England and Wales
- Principal place of business
- London, UK
- Regulatory status
- Authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority (FRN 800542)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence
- Complaints
- Financial Ombudsman Service
-
15. Monzo
Fixed Rate Cash ISA (3 years)
4.60%
AER fixed
- Access
- 3 years fixed
- Minimum
- £500
- Transfers in
- No
- Flexible
- Yes
Details and provider information
- Withdrawals
- No access during the term. You can only close the whole Pot early and give up some of the interest earned (the app shows how much).
- How to open
- App
- Your money is held by
- Monzo Bank Limited
- Good to know
- Needs a Monzo current account (free); no ISA transfers in. At maturity the money moves to an Instant Access Pot.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- More from Monzo
- All Monzo Cash ISAs compared
- Legal name
- Monzo Bank Limited
- Country of incorporation
- England and Wales
- Principal place of business
- London, UK
- Regulatory status
- Monzo Bank Limited is authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority (FRN 730427)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence
- Complaints
- Financial Ombudsman Service
-
16. M&S Bank
M&S Cash ISA Fixed Rate Savings option, 3 year
4.45%
AER fixed
- Access
- 3 years fixed
- Minimum
- £500
- Transfers in
- Yes
- Flexible
- No
Details and provider information
- Withdrawals
- No partial withdrawals. Withdrawing or transferring out the whole fixed-rate option early costs a £100 fee.
- How to open
- Online, phone or post
- Your money is held by
- HSBC UK Bank plc
- Good to know
- Limited offer, subject to availability. Open to anyone aged 18 or over.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- More from M&S Bank
- All M&S Bank Cash ISAs compared
- Legal name
- HSBC UK Bank plc (trading as M&S Bank)
- Country of incorporation
- England and Wales
- Principal place of business
- Birmingham, UK
- Regulatory status
- HSBC UK Bank plc is authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority (FRN 765112)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence, shared with HSBC UK and first direct
- Complaints
- Financial Ombudsman Service
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17. Monmouthshire Building Society
3 Year Fixed Rate Cash ISA
4.40%
AER fixed
- Access
- 3 years fixed
- Minimum
- £1,000
- Transfers in
- Yes
- Flexible
- No
Details and provider information
- Withdrawals
- No withdrawals after the 14-day cancellation period. Closing or transferring to another provider early costs 270 days' interest.
- How to open
- App, Branch
- Your money is held by
- Monmouthshire Building Society
- Good to know
- UK residents only, excluding Northern Ireland. Branch, agency or app only (no web application). Payments accepted in the first 30 days only.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- Legal name
- Monmouthshire Building Society
- Country of incorporation
- United Kingdom
- Principal place of business
- Newport, Wales, UK (Monmouthshire House, John Frost Square, Newport NP20 1PX)
- Regulatory status
- Authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority. Financial Services Register Number: 206052 (FRN 206052)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence
- Complaints
- Financial Ombudsman Service
-
18. Ford Money
Fixed Cash ISA (3 Years)
4.15%
AER fixed
- Access
- 3 years fixed
- Minimum
- £500
- Transfers in
- Yes
- Flexible
- No
Details and provider information
- Withdrawals
- Close or transfer out early for a term breakage charge of 270 days' gross interest. After early closure you can't open another cash ISA that tax year.
- How to open
- Online
- Your money is held by
- FCE Bank plc
- Good to know
- Online only; needs a Connected UK bank account. Fund within 21 days of opening; ISA transfers must complete within 21 days of applying.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- Legal name
- FCE Bank plc (trading as Ford Money)
- Country of incorporation
- England and Wales
- Principal place of business
- Essex, UK (registered address: Arterial Road, Laindon, Essex SS15 6EE)
- Regulatory status
- Ford Money is a trading style of FCE Bank plc, which is authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority under Firm Reference Number 204469. Registered in England and Wales, registration number 772784 (FRN 204469)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence
- Complaints
- Financial Ombudsman Service
-
19. Metro Bank
Fixed Rate Cash ISA (3 years)
3.65%
AER fixed
- Access
- 3 years fixed
- Minimum
- None
- Transfers in
- Yes
- Flexible
- No
Details and provider information
- Withdrawals
- No partial withdrawals; closing or transferring out early loses 180 days' interest (or all interest earned if less). Not a flexible ISA.
- How to open
- Branch (Metro Bank store)
- Your money is held by
- Metro Bank PLC
- Good to know
- Opened in a Metro Bank store only. Start any ISA transfer within 7 days of opening and complete it within 30 days.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- More from Metro Bank
- All Metro Bank Cash ISAs compared
- Legal name
- Metro Bank PLC
- Country of incorporation
- England and Wales
- Principal place of business
- London, UK
- Regulatory status
- Authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority (FRN 488982)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence
- Complaints
- Financial Ombudsman Service
Calculate your returns
For the fixed term.
For how long
Interest earned
Balance at the end
Open the full calculator
How a 3 year fixed rate ISA works
You pay in a lump sum, or a few payments within a short window after opening, and the provider fixes the rate for 3 years. The rate does not move if Bank Rate changes during the term. Interest is tax-free, like any Cash ISA, and the AER shows what a year's interest is worth if it stays in the account.
A 3 year fix or another term?
Here is what £10,000 would earn at the highest rate in our tables for each common term, if you leave the money and its interest in for the whole term. A longer fix earns more in total, but ties the money up for longer.
| Fixed for | Highest rate | £10,000 earns |
|---|---|---|
| 1 year | 5.00% | £500 |
| 18 months | 4.70% | £713 |
| 2 years | 5.10% | £1,046 |
| 3 years | 5.15% | £1,626 |
| 4 years | 4.70% | £2,017 |
| 5 years | 5.25% | £2,915 |
For comparison, the highest easy access rate in our tables was 4.86% AER on 6 October 2026. That rate is variable, so it can fall or rise during a year; a fixed rate cannot. See the easy access Cash ISAs.
What if you need the money early?
Most fixes let you leave early for a charge, usually a number of days' interest on the amount you take out or on the whole balance. Some only let you close the whole account. Of the 19 fixes for 3 years in our table, 15 state a single charge in days of interest. It runs from 90 to 270 days, and 270 days is the most common. If you have not yet earned enough interest to cover the charge, some providers take the rest from your savings. Open the details on any account above to see its rule. To see what a charge would cost on your own savings, use our fixed rate ISA penalty calculator.
Does the Cash ISA limit affect a fix past 6 April 2027?
A 3 year fix opened in November 2026 runs to about November 2029. The Cash ISA limit for new money stays £20,000 a year: the cut to £12,000 planned from 6 April 2027 was cancelled in the Budget on 28 October 2026. See the Cash ISA limit guide and why the April 2027 deadline matters less.
When the term ends
Providers usually write before the fix ends. If you do nothing, many move the money into an easy access or maturity account at a lower variable rate. You can choose a new fix with the same provider, or move the money to another provider's Cash ISA by transfer, which keeps it tax-free. See how ISA transfers work.
Questions people ask
What is the best 3 year fixed rate ISA?
Ranked by rate alone, the highest 3 year fixed rate Cash ISA in our tables on 6 October 2026 paid 5.15% AER, from Castle Trust Bank. Rates change often, so check the table on this page, and check the account's conditions before you apply.
How much does £10,000 earn in a 3 year fixed rate ISA?
At 5.15% AER, £10,000 left in for the full 3 years earns about £1,626 in tax-free interest, assuming the interest stays in the account. Try your own amount in the Cash ISA interest calculator.
Can I take money out of a 3 year fixed rate ISA early?
Usually, but at a cost, and some accounts only let you close the whole account. Of the 19 fixes for 3 years in our table, 15 state a single charge in days of interest. It runs from 90 to 270 days, and 270 days is the most common. Each account's rule is in its details on this page.
Can I add money to a 3 year fixed rate ISA later?
Usually only during a short window after you open it. Many fixes accept payments for a set number of days, after which no more money can go in. The details for each account on this page show its window.
Is my money protected in a 3 year fixed rate ISA?
Deposits with an authorised UK bank, building society or credit union are protected by the Financial Services Compensation Scheme up to £120,000 per person, per banking licence. A few brands share one licence, which the details for each account show.