How much cash should you keep? What the 2027 Cash ISA changes mean for your financial plan

From April 2027, most people under 65 will be limited to £12,000 of new Cash ISA subscriptions each tax year.

It sounds like a savings decision. But it raises a much more useful financial-planning question: How much accessible cash does your life actually require?

For one household, the answer might be much less than £12,000. For another, it could be £40,000, £80,000 or considerably more because a house purchase, tax bill, uncertain income, major expense or period without earnings is approaching.

And there is another complication. Money held outside an ISA is not automatically taxed. Depending on your income and the interest earned, ordinary savings may already generate interest without creating an Income Tax bill.

So there are really two different questions: How much cash does your financial plan need? And what is the most appropriate way to hold it? The first should come before the second.

£12,000 is an ISA limit. It is not a financial plan.

For the current 2026/27 tax year, adults can subscribe up to £20,000 across their ISAs. There is currently no separate £12,000 Cash ISA sub-limit. The £20,000 can be allocated between permitted ISA types, subject to the rules applying to each type. GOV.UK confirms the current £20,000 ISA allowance.

The Government has confirmed that the position will change from 6 April 2027.

For people under 65, the annual Cash ISA subscription limit will become £12,000, while the overall annual ISA allowance will remain £20,000.

For people aged 65 and over, the Cash ISA limit will remain £20,000. Entitlement to that higher limit will apply from the beginning of the tax year in which the person turns 65, rather than from their 65th birthday. The Government's ISA reform factsheet explains the policy.

So someone under 65 will not have their overall ISA allowance cut from £20,000 to £12,000. What changes is how much of that allowance can normally be used for a Cash ISA.

The Government is introducing additional measures intended to prevent people sidestepping the lower Cash ISA limit.

Under the announced rules, people under 65 will no longer be able to transfer money from a Stocks and Shares ISA or Innovative Finance ISA into a Cash ISA. Transfers in the other direction will remain possible.

This is a change from the current position, under which GOV.UK says ISA savings can generally be transferred between ISA types, including money invested in previous tax years. Current ISA transfer rules are explained here.

The Government is also targeting cash held inside non-Cash ISAs. Cash will still be permitted temporarily inside Stocks and Shares and Innovative Finance ISAs, but a 22% charge is intended to apply to interest or alternative-finance returns paid on that cash. The ISA manager, rather than the individual saver, will pay the charge to HMRC.

Money Market Funds will initially be treated as cash-like investments. They can still form part of a non-Cash ISA portfolio, but a portfolio made up entirely of cash-like investments would not qualify under the proposed rules.

People aged 65 and over get different treatment for the Cash ISA limit and transfer restriction, but they are not exempt from all of the new rules. The charge on interest earned on cash inside non-Cash ISAs and the restriction on portfolios consisting entirely of cash-like assets are still intended to apply. See the Government's ISA reform factsheet.

This distinction matters. The Government's decision to introduce the £12,000 limit is confirmed policy, but the legislation containing the detailed implementation remains draft.

HMRC published the draft Individual Savings Account (Amendment) Regulations 2026 on 16 July 2026. The technical consultation has now closed. As at 10 August 2026, HMRC still describes these as draft regulations, while the Government says the regulations will be laid in autumn 2026 ahead of their intended introduction on 6 April 2027. The HMRC consultation and draft legislation are available here.

That means some technical detail could still change before implementation.

It is also worth being clear about what the £12,000 figure is. It is an annual subscription limit, not a cap on the total amount somebody may already have accumulated in Cash ISAs. The reform does not mean an existing £50,000 or £100,000 Cash ISA balance somehow has to be reduced to £12,000.

This is where the story becomes more interesting.

Interest received inside an ISA is tax-free. But interest received outside an ISA is not automatically taxable.

Most people have one or more allowances that can allow some savings interest to be received without paying Income Tax. HMRC identifies three possible mechanisms: unused Personal Allowance, the starting rate for savings and the Personal Savings Allowance. Exactly which apply depends on the person's other income. HMRC explains the savings-interest rules here.

For most savers, the best-known allowance is the Personal Savings Allowance.

Under the current rules, a basic-rate taxpayer can receive up to £1,000 of savings interest within the Personal Savings Allowance, a higher-rate taxpayer up to £500, and an additional-rate taxpayer receives no Personal Savings Allowance. HMRC sets out the current allowances here.

The important word is interest. The allowance does not mean a basic-rate taxpayer can only hold £1,000 outside an ISA. It means up to £1,000 of qualifying savings interest can currently fall within their Personal Savings Allowance.

Purely as an illustration, £25,000 earning 4% generates £1,000 of annual interest. £20,000 earning 5% also generates £1,000. For a higher-rate taxpayer with a £500 Personal Savings Allowance, £12,500 at 4% or £10,000 at 5% generates £500 of annual interest.

These are not recommended savings amounts. They simply illustrate the relationship between savings balances, interest rates and the tax allowance. The real calculation needs to include all relevant taxable savings interest, and the interest itself is included when determining someone's Income Tax band.

The Personal Savings Allowance is not the whole story.

Someone whose other income is relatively low may also qualify for the starting rate for savings. HMRC says this can provide a 0% tax rate on up to £5,000 of savings interest.

The full £5,000 may be available where other income does not exceed the Personal Allowance. It then reduces by £1 for every £1 of other income above the Personal Allowance and disappears once other income reaches £17,570 under the current rules. HMRC explains the starting rate for savings here.

Unused Personal Allowance may also be available against savings income.

That means somebody with relatively low employment or pension income could potentially receive considerably more savings interest tax-free than the headline £1,000 Personal Savings Allowance suggests.

Again, this is an individual tax calculation, not a reason to arrange savings in a particular way. But it reinforces an important planning point: for some people, putting cash inside an ISA may provide no immediate Income Tax saving at all.

There is an equally important qualification. Even where ordinary savings interest currently fits within someone's allowances, an ISA can still have future tax value.

Interest inside an ISA does not use the Personal Savings Allowance. If savings grow, interest rates increase or someone's income moves them into a different tax position, interest that was previously tax-free outside an ISA may become taxable.

That is particularly relevant because the Government has also announced higher tax rates for savings income from 6 April 2027.

From the 2027/28 tax year, savings income above the available 0% allowances will be taxed at separate rates of 22% at the savings basic rate, 42% at the savings higher rate and 47% at the savings additional rate.

The Government says the structure of the starting rate for savings and Personal Savings Allowance will remain unchanged. The changes to savings-income tax rates will apply UK-wide. HMRC's technical note explains the new rates.

There is therefore a slightly unusual combination of changes arriving in April 2027. For most under-65s, the amount of new cash that can go into a Cash ISA will fall. At the same time, the tax rate applied to savings income that does become taxable will rise.

That makes tax efficiency worth understanding. But it still does not answer the more fundamental question: How much cash should you have in the first place?

There is another misconception worth clearing up.

Banks and building societies report savings interest to HMRC. For employees and pensioners, HMRC can normally collect tax due by adjusting the individual's tax code. People already completing Self Assessment report relevant interest through their return.

HMRC says people need to register for Self Assessment if their income from savings and investments exceeds £10,000, although other circumstances can also create a filing requirement. HMRC explains how tax on savings interest is collected.

So crossing the Personal Savings Allowance does not automatically mean somebody suddenly has to complete a tax return.

Once the tax mechanics are stripped away, the central planning issue becomes clearer. Tax allowances tell you how money is treated. They do not tell you what the money is needed for.

A first-time buyer may deliberately hold £40,000 or £60,000 in cash because most of it is intended for a house purchase. A self-employed consultant might need several months of living costs, working capital and a substantial amount reserved for tax. A family might be expecting parental leave, childcare costs or major home repairs. Someone approaching retirement might deliberately accumulate accessible money to cover the period between stopping work and receiving pension or State Pension income.

All of these people could have legitimate reasons for holding more than £12,000 in cash. Another household with secure employment, predictable outgoings and no major planned expenditure may need considerably less.

The right starting question is therefore not How much cash can I shelter inside an ISA? It is What does my cash need to do?

One useful way to think about household cash is to stop treating every savings account as one undifferentiated pot. Instead, give each part of the money a purpose.

Most household cash requirements fall broadly into four categories.

MoneyHelper suggests three to six months of essential outgoings in an instant-access savings account as a useful rule of thumb for an emergency fund. It is a starting point, not a universal formula. MoneyHelper's emergency-savings guidance is here.

A two-income household with stable employment may look at this differently from a household dependent on one income. A freelancer whose monthly income fluctuates considerably may want a larger cushion than someone receiving a highly predictable salary.

The question is not whether three months or six months is objectively correct. It is what level of disruption you want your household to be capable of absorbing.

This is where an emergency-fund rule can become misleading. Money you already expect to spend should not really be counted as emergency savings.

Suppose somebody has £15,000 earmarked as an emergency reserve, £30,000 for a house purchase and £8,000 reserved for tax. Their £53,000 cash balance does not necessarily represent an oversized emergency fund. Most of the money already has a job.

The same applies to wedding costs, education, a car replacement, moving expenses, planned travel, care costs or a period of unpaid leave.

Someone receiving a predictable salary every month faces a different cashflow problem from someone whose income varies significantly.

For a self-employed person, contractor, landlord or commission-based worker, a large balance today may have to support several weaker months later. Part of the apparent cash might also already belong to HMRC.

Our article Making Tax Digital: the cashflow wake-up call for side-income households looks at the importance of separating tax set-asides and understanding the household effect of irregular income.

A healthy bank balance can therefore be deceptive. The useful question is not simply how much money is there today. It is how much has already been committed to future obligations.

There is no universal percentage of household wealth that should be held as cash because the job cash performs changes over time.

A younger saver may need a relatively modest emergency reserve while building a much larger deposit for a first home. A family may need more resilience because fixed expenditure has grown and parental leave or childcare can temporarily change household income. Someone moving into self-employment may need more accessible money because earnings have become less predictable.

Someone approaching retirement may deliberately build cash for known expenditure or to bridge an income gap. A retiree may have predictable pension income covering ordinary expenditure but still need accessible money for larger planned costs and contingencies.

This is exactly why Planiva's whole-life planning approach focuses on practical decisions throughout adult life rather than treating financial planning as something that starts at retirement.

Retirement is a good example of why one cash balance can conceal several different purposes.

Imagine somebody stops work at 63 but their State Pension begins later. Money deliberately reserved to meet spending during that gap is bridge funding. It is planned. That is different from the emergency reserve they may still need if something unexpected happens.

It may also be different from money put aside for a new car, home improvements or major travel during the early years of retirement.

Likewise, somebody taking tax-free pension cash should ideally understand what that money is intended to achieve rather than withdrawing it simply because it has become available. That is the principle behind our article How to think about tax-free pension cash.

Again, the important distinction is purpose.

Cash is often described as safe. That is understandable because its nominal value does not normally fluctuate like market investments. But it helps to separate several different ideas.

Liquidity is whether money can readily be converted into something you can spend.

Accessibility is whether there are practical restrictions on getting at it when needed.

Security is about how predictable the amount available will be.

Inflation risk is the possibility that the same number of pounds buys less in future.

Investment risk can include the possibility that an asset falls in value, particularly at the point when the money is required.

Time horizon is how long you realistically have before the money needs to perform its job.

These risks are different. Cash can provide valuable short-term certainty and accessibility while still losing purchasing power over long periods. Assets whose prices move can behave differently, but may create a problem if they must be sold at an inconvenient time.

There is no need for this article to turn that into a recommendation for one over the other. The planning question comes first: When is the money needed, and how certain must its value and availability be at that point?

This may be the most useful question of all. Sometimes a cash balance grows deliberately. Sometimes it just grows.

Salary accumulates. A bonus arrives. A property is sold. A pension lump sum is taken. Spending is lower than expected. An inheritance arrives.

Years later, there can be a substantial amount of cash without a clear answer to: What is this money for?

That does not automatically mean it should be invested. It does not automatically mean it should remain as cash. And it does not automatically mean it needs to be squeezed into an ISA.

It means it needs a purpose. How much is required for normal spending? How much provides genuine resilience? What bills and major expenditure are approaching? How much is reserved for tax? Could income disappear or reduce? What major life changes are planned? How much money has no likely use for many years?

Those questions turn a bank balance into a financial plan.

The amount of cash a household needs becomes easier to understand when it is placed on a timeline.

Start with today's balances. Add recurring income. Add essential and discretionary spending. Add known major costs. Set aside liabilities such as tax. Identify the emergency reserve you want to protect. Then test what happens when reality moves away from the expected path.

The number that matters is not simply today's cash balance. It is the lowest point the household might reasonably reach while those commitments are being met.

Planiva's Cash Flow Planner is designed for exactly this type of question.

It can model household cashflow over one to five years, including recurring income and expenditure, one-off events and different timing assumptions. Scenarios can then be compared to see where cash may come under pressure.

That makes it possible to compare questions such as six months of emergency cash versus nine months, a house purchase next year versus the year after, normal income versus six months of reduced earnings, retiring now versus working another year, or a major purchase today versus delaying it.

Planiva's Plan vs actual feature can then compare the saved cashflow plan with real month-end balances, helping show whether the assumptions are still connected to reality.

The aim is not to produce a permanent magic cash number. It is to understand what your money needs to do, when it needs to do it and how robust the plan remains if circumstances change.

The Cash ISA reforms matter.

From 6 April 2027, most people under 65 will be limited to £12,000 a year of new Cash ISA subscriptions within an unchanged £20,000 overall ISA allowance. The Government is also changing transfer rules and introducing restrictions around cash and cash-like holdings inside non-Cash ISAs. The detailed regulations remain draft as at 10 August 2026.

At the same time, savings held outside an ISA are not automatically taxed. Basic-rate taxpayers currently have a £1,000 Personal Savings Allowance, higher-rate taxpayers £500, and people with sufficiently low other income may also benefit from the starting rate for savings and unused Personal Allowance. From April 2027, savings income that does become taxable will face rates of 22%, 42% and 47%, while those savings allowances are intended to remain unchanged.

All of that affects how cash is taxed. None of it tells you how much cash your life requires.

Start there instead. Some cash keeps everyday life moving. Some provides emergency resilience. Some is already committed to future expenditure. Some bridges a temporary period of lower income. And some may simply have accumulated without a defined purpose.

The Cash ISA rules can help determine how some of that money is held. They should not determine the amount.

£12,000 is an ISA limit. It isn't a financial plan.

Planiva provides planning and scenario modelling for information and decision support. It does not provide regulated financial, investment, tax or legal advice, recommend investments or funds, or recommend ISA providers.

Tax treatment depends on individual circumstances and can change. Investment and ISA decisions can also have long-term consequences. Consider regulated financial or professional tax advice where appropriate.

GOV.UK: Individual Savings Accounts

GOV.UK: Current ISA transfer rules

HMRC: ISA reform 2027 anti-circumvention rules

HMRC: Draft Individual Savings Account (Amendment) Regulations 2026

HMRC: Tax on savings interest

HMRC: Changes to tax rates for savings income from April 2027

MoneyHelper: How much to save for an emergency