How much cash should you keep? Why the £20,000 Cash ISA limit isn't a financial plan

Budget 2026 has reversed the Government's planned reduction in the Cash ISA allowance. From April 2027, eligible adults will continue to be able to subscribe up to £20,000 annually to Cash ISAs, rather than facing the proposed £12,000 restriction.

That's welcome clarity for savers. But it doesn't answer a more important question: how much accessible cash does your household actually need?

For one household, the answer might be considerably less than £20,000. For another, it could be £40,000, £80,000 or more because a house purchase, tax bill, uncertain income, major expense or period without earnings is approaching.

And there's another complication. Savings held outside an ISA aren't automatically taxed. Depending on your income and the interest earned, ordinary savings may generate interest without creating an Income Tax liability.

The 2026 Budget also confirmed higher tax rates on savings income from April 2027, making the distinction between taxable and tax-free interest more relevant.

There are really two questions: how much cash does your financial plan need, and how should that money be held? The first question should come before the second.

In November 2025, the Government announced plans to restrict annual Cash ISA subscriptions to £12,000 for most people under 65 from April 2027.

The proposals also included restrictions on transfers into Cash ISAs and measures targeting cash and cash-like investments held within other types of ISA. Draft regulations were published during 2026.

However, on 28 October 2026, the Government reversed its decision. HMRC confirmed that the £12,000 restriction and associated anti-circumvention measures will not take effect.

The Government is instead exploring a new incentive for people investing in a Stocks and Shares ISA for the first time. The details have not yet been agreed.

The distinction matters because an announced policy can be reversed before implementation. Financial plans should reflect current rules and confirmed changes, while treating uncertain future policies as scenarios rather than facts.

Interest received inside an ISA is free from Income Tax. 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 allowances apply depends on the individual's other income and tax circumstances.

This means that some households may already be receiving all their ordinary savings interest tax-free, even without using a Cash ISA.

That does not make an ISA irrelevant. It means the immediate tax benefit of holding cash inside one depends on the circumstances.

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

The important word is interest. A £1,000 Personal Savings Allowance does not mean somebody can only hold £1,000 outside an ISA. It means up to £1,000 of qualifying savings interest can fall within that allowance.

For example, £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 earning 4% generates £500 of interest.

These are illustrations, not recommended savings amounts. The real calculation must include all relevant taxable savings interest, and that interest can itself affect the taxpayer'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. This can provide a 0% tax rate on up to £5,000 of savings interest.

The full £5,000 may be available where other taxable income does not exceed the standard Personal Allowance. It then reduces by £1 for every £1 of other income above that allowance and disappears once other income reaches £17,570 under the current standard thresholds.

Unused Personal Allowance may also be available against savings interest.

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.

For some people, holding cash inside an ISA may therefore provide no immediate Income Tax saving. But future income, interest rates and tax rules could change that position.

Although Budget 2026 retained the £20,000 Cash ISA allowance, it also announced further increases to Income Tax rates on taxable savings interest from 6 April 2027.

The announced rates are 24% for basic-rate savings income, 44% for higher-rate savings income and 49% for additional-rate savings income. These compare with the current 2026/27 rates of 20%, 40% and 45%. The changes require legislation and are intended to apply across the UK.

Importantly, these rates apply to taxable savings interest, not the savings balance itself. The Personal Savings Allowance, starting rate for savings and unused Personal Allowance remain relevant.

Consider someone earning £2,000 annually in savings interest outside an ISA. Assume they are a basic-rate taxpayer and qualify for the full £1,000 Personal Savings Allowance.

That leaves £1,000 of taxable interest. At the current 20% rate, the tax would be £200. At the announced 24% rate, it would rise to £240.

That's an additional £40 annually, assuming their circumstances and interest income remain unchanged.

Someone whose interest remains entirely within their available allowances may have no savings-income tax liability at all. Interest earned within an ISA remains exempt from Income Tax.

The Budget changes the tax calculation. It does not determine how much cash your household needs.

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.

The announced increases in savings-income tax rates from April 2027 make this distinction worth understanding.

However, the existence of an ISA allowance does not mean that everyone should automatically hold £20,000 in cash or subscribe the maximum amount every year.

The purpose, accessibility and time horizon of the money remain fundamental planning considerations.

Banks and building societies generally report savings interest to HMRC. For employees and pensioners, HMRC can often collect tax due by adjusting their tax code.

People already completing Self Assessment report relevant savings interest through their tax return.

HMRC generally requires people with more than £10,000 of income from savings and investments to register for Self Assessment, although other circumstances can also create a filing requirement.

Crossing the Personal Savings Allowance does not automatically mean somebody must start completing a Self Assessment return.

The distinction between having a tax liability and needing to submit a tax return is important, particularly for households with several income sources.

Tax allowances tell you how money is treated. They do not tell you what that 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 money 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 these households could have legitimate reasons for holding more than £20,000 in cash. Another household with secure employment, predictable expenditure and no major planned commitments may need considerably less.

The right starting question is not how much cash can be sheltered inside an ISA. It is what the cash needs 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 into four broad categories. Separating them makes it easier to understand how much money is genuinely available and how much is already committed.

MoneyHelper suggests three to six months of essential outgoings in an instant-access savings account as a useful emergency-fund rule of thumb.

It is a starting point, not a universal formula.

A two-income household with stable employment may look at this differently from a household dependent on one income.

A freelancer whose income fluctuates considerably may need to test a larger reserve than someone receiving a highly predictable salary.

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

Money you already expect to spend should not 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, vehicle replacement, moving expenses, planned travel, care costs or a period of unpaid leave.

Separating planned expenditure from emergency reserves helps avoid counting the same money twice.

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 be needed for future tax payments.

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.

Our article on Making Tax Digital and cashflow explores why irregular income, tax set-asides and the timing of payments matter for household financial planning.

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 why Planiva's whole-life planning approach focuses on financial decisions throughout adult life, not only 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 at 67. Money reserved to meet spending during those four years is bridge funding. It is planned expenditure.

That is different from an emergency reserve, or money set aside for a replacement car, home improvements or major travel during the early years of retirement.

Likewise, somebody taking tax-free pension cash should understand what that money is intended to achieve rather than withdrawing it simply because it has become available.

Our articles on bridging the gap before State Pension and thinking about tax-free pension cash explore these decisions in greater detail.

The important distinction is purpose, timing and the consequences for the wider retirement plan.

Cash is often described as safe because its nominal value does not normally fluctuate like market investments.

But several different risks need to be distinguished.

Cash can provide valuable short-term certainty and accessibility while still losing purchasing power over longer periods because of inflation.

Other assets may behave differently, but their values can fluctuate and create problems if they must be sold at an inconvenient time.

This is not an argument for one type of asset over another. The planning question comes first: when is the money needed, and how certain must its value and availability be?

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 the money is actually 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 placed inside an ISA.

The Government's decision to retain the £20,000 Cash ISA limit removes much of the uncertainty created by the earlier proposals. But tax rules can still change, and household circumstances may change too.

Someone whose savings interest falls within their tax-free allowances today could face a different position if interest rates, savings balances or other income change.

The useful starting point is to identify how much is needed for normal spending, emergency resilience, tax, planned expenditure and possible changes in income.

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, essential and discretionary expenditure, known major costs and future 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 its commitments are being met.

A financial plan becomes more useful when it can be tested against different outcomes rather than relying on a single optimistic projection.

Planiva's Cash Flow Planner is designed to help households explore these questions.

It can model cashflow over one to five years, including recurring income and expenditure, one-off events and different timing assumptions.

Scenarios can be compared to see where cash may come under pressure and how changing circumstances affect projected balances.

Planiva's Plan vs Actual feature can also compare a saved cashflow plan with real month-end balances, helping users understand whether their assumptions still reflect 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.

Budget 2026 has preserved the £20,000 annual Cash ISA limit while announcing higher tax rates on taxable savings interest from April 2027.

Both developments matter. But neither tells you how much cash your household needs.

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 useful starting point is to understand those requirements.

Once you understand the purpose and timing of your cash requirements, you can explore how different tax treatments and financial assumptions affect your plan.

£20,000 is an ISA allowance. It isn't a financial plan.

Planiva provides financial planning information and scenario modelling for educational and decision-support purposes.

It does not provide regulated financial advice, personalised tax or legal advice, or recommendations about savings accounts, investments, funds or ISA providers.

Tax treatment depends on individual circumstances and may change. Significant financial decisions may warrant advice from an appropriately qualified professional.

HMRC: Tax-free savings newsletter 24, October 2026 — https://www.gov.uk/government/publications/tax-free-savings-newsletter-24/tax-free-savings-newsletter-24-october-2026

HMRC: Budget 2026 Overview of Tax Legislation and Rates — https://www.gov.uk/government/publications/budget-2026-overview-of-tax-legislation-and-rates-ootlar/budget-2026-overview-of-tax-legislation-and-rates-ootlar

GOV.UK: Individual Savings Accounts — https://www.gov.uk/individual-savings-accounts

GOV.UK: Tax on savings interest — https://www.gov.uk/apply-tax-free-interest-on-savings

MoneyHelper: How much to save for an emergency — https://www.moneyhelper.org.uk/en/savings/how-to-save/emergency-savings-how-much-is-enough