Best 18 month fixed rate ISAs
2 Cash ISAs fixed for 18 months, 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 30 October 2026 paid 4.70% AER.
18 month fixes at a glance
- Highest rate
- 4.70% AER
- TSB
- £10,000 at that rate earns
- £713
- Over 18 months, tax-free
- Accounts compared
- 2
- Checked on 30 October 2026
- Highest easy access rate
- 4.86% AER
- Variable, so it can change
Best 18 month fixed rate ISAs
Checked 30 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. TSB
Fixed Rate Cash ISA (18 month term)
4.70%
AER fixed
- Access
- 18 months fixed
- Minimum
- None
- Transfers in
- Yes
- Flexible
- Yes
Details and provider information
- Withdrawals
- Withdrawals are allowed after 14 days but cost 135 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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2. The Cambridge Building Society
18 Month Fixed Rate ISA (Issue 22)
4.60%
AER fixed
- Access
- 18 months fixed
- Minimum
- £500
- Transfers in
- Yes
- Flexible
- No
Details and provider information
- Withdrawals
- Withdrawals are allowed at any time but cost 150 days' interest on the amount withdrawn. Not a flexible ISA.
- How to open
- Branch, Phone, Post
- Your money is held by
- The Cambridge Building Society
- Good to know
- Not available online: open in branch, by phone or by post. Transfers in and payments are accepted only within 30 days of opening.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- Legal name
- The Cambridge Building Society
- Country of incorporation
- United Kingdom
- Principal place of business
- Cambridge, UK (registered office: 51 Newmarket Road, Cambridge CB5 8EG)
- Regulatory status
- Authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and Prudential Regulation Authority (Registration Number 157223) (FRN 157223)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence
- Complaints
- Financial Ombudsman Service
Calculate your returns
For the fixed term.
Interest earned
Balance at the end
Open the full calculator
Fixed rate ISAs for 13 to 21 months
Checked 30 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. Skipton Building Society
19 Month Fixed Rate Cash ISA
4.81%
AER fixed
- Access
- 19 months 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 90 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 2 December 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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2. Yorkshire Building Society
Fixed Rate Cash eISA until 30 November 2027
4.55%
AER fixed
- Access
- Fixed to Nov 2027
- Minimum
- £100
- Transfers in
- Yes
- Flexible
- No
Details and provider information
- Withdrawals
- No withdrawals before the end date, and closing early costs 90 days' interest apart from exceptions such as critical illness, death or redundancy.
- How to open
- Online or app
- Your money is held by
- Yorkshire Building Society
- Good to know
- Fixed until 30 November 2027. Limited offer that can come off sale without notice. After it closes to new customers you have at least 30 days to add money.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- More from Yorkshire Building Society
- All Yorkshire Building Society Cash ISAs compared
- Legal name
- Yorkshire Building Society
- Country of incorporation
- United Kingdom
- Principal place of business
- Bradford, UK
- Regulatory status
- Authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority (FRN 106085)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence, shared with Chelsea Building Society and Norwich & Peterborough Building Society
- Complaints
- Financial Ombudsman Service
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3. Marsden Building Society
Fixed Rate Cash ISA (Issue 337)
4.40%
AER fixed
- Access
- Fixed to Jun 2028
- Minimum
- £5,000
- Transfers in
- Yes
- Flexible
- No
Details and provider information
- Withdrawals
- No partial withdrawals before maturity. Closing or transferring out early costs 210 days' interest.
- How to open
- Branch
- Your money is held by
- Marsden Building Society
- Good to know
- Branch only, at one of Marsden's Lancashire branches. Matures on 30 June 2028. ISA transfers in only at opening.
- Rate checked
- On the provider's own site on 30 October 2026. Source
- Legal name
- Marsden Building Society
- Country of incorporation
- United Kingdom
- Principal place of business
- Nelson, Lancashire, UK (principal office: 6-20 Russell Street, Nelson, Lancashire BB9 7NJ)
- Regulatory status
- Authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority. Registered in the Financial Services Register under no: 206050 (FRN 206050)
- Deposit protection
- FSCS, up to £120,000 per person per banking licence
- Complaints
- Financial Ombudsman Service
Calculate your returns
For the fixed term.
Interest earned
Balance at the end
Open the full calculator
How an 18 month 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 18 months. 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.
An 18 month 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 30 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 2 fixes for 18 months in our table, both state a single charge in days of interest: 135 days on one and 150 on the other. 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?
An 18 month fix opened in November 2026 runs to about May 2028. 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 18 month fixed rate ISA?
Ranked by rate alone, the highest 18 month fixed rate Cash ISA in our tables on 30 October 2026 paid 4.70% AER, from TSB. 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 an 18 month fixed rate ISA?
At 4.70% AER, £10,000 left in for the full 18 months earns about £713 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 an 18 month fixed rate ISA early?
Usually, but at a cost, and some accounts only let you close the whole account. Of the 2 fixes for 18 months in our table, both state a single charge in days of interest: 135 days on one and 150 on the other. Each account's rule is in its details on this page.
Can I add money to an 18 month 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 an 18 month 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.