How Much Tax to Set Aside UK 2026/27 — Self Assessment Reserve

If you are self-employed, freelance, a landlord or receive other untaxed income, the amount to set aside is usually more than “this month’s tax”. A Self Assessment bill can include the balancing payment for the year just filed and a first Payment on Account towards the following year. A second Payment on Account can arrive in July, while a change in profit can create a further balancing amount later.

The practical question is how much cash should be reserved now, and when will HMRC expect it? The Tax Reserve Assistant can organise income, tax, National Insurance and payment dates into a scenario. It is an estimate. Your submitted return, HMRC statement and payment instructions control the legal amount.

What a Self Assessment reserve is for

A tax reserve is cash set aside for liabilities that are not being collected fully through PAYE or another withholding route. It is not a separate HMRC account and it does not reduce the tax owed. It is a household or business cash-management method.

Depending on your circumstances, the reserve may need to cover:

• Income Tax on self-employed, property, savings, dividend or other income;
• Class 4 National Insurance where the self-employed rules apply;
• Class 2 or other National Insurance amounts where relevant under the current rules;
• the balancing payment for the year being filed;
• the first and second Payments on Account for the next year;
• Capital Gains Tax that must be paid through the relevant route;
• student-loan repayments collected through Self Assessment; and
• VAT, PAYE or Corporation Tax in a separate business reserve.

Do not combine every tax into one unexplained percentage. A sole trader’s Self Assessment reserve is different from a limited company’s Corporation Tax reserve, an employer’s PAYE account and a VAT balance. Use separate pots or clear ledger lines.

Payments on Account create the cash-flow shock

GOV.UK says Payments on Account are advance payments towards the next tax bill, including Class 4 National Insurance where applicable. They are normally two instalments, each half of the previous year’s tax owed, due by midnight on 31 January and 31 July.

They are normally required unless the previous year’s tax owed was less than £1,000 or more than 80% of the tax was already collected outside Self Assessment, such as through a tax code or tax deducted at source. The exact calculation is shown on the Self Assessment statement.

The important distinction is between:

This is why a first Self Assessment bill can feel unexpectedly large. If there were no prior Payments on Account, the January amount may contain the full first-year calculation plus the first instalment for the next year. Build the reserve before filing, not after the statement arrives.

The annual payment timeline

The tax year and the payment year are different. For a normal online return, the filing deadline and payment deadline are not interchangeable. GOV.UK’s payment guidance currently identifies 31 January for the balancing payment and first Payment on Account, and 31 July for the second Payment on Account.

Use a calendar with four columns:

The dates do not mean that every taxpayer owes the same amount. They describe the standard payment structure. Check your HMRC statement, payment reference and any special arrangement before sending money.

How to estimate a monthly reserve

Start with expected taxable profit, not gross invoices. A simple planning model is:

1. Estimate annual turnover or other untaxed income.
2. Subtract expenses that are allowable under the relevant rules and supported by records.
3. Add or adjust for employment income, property income, dividends, savings, pension contributions and other taxable sources.
4. Estimate Income Tax and National Insurance using the correct tax year and circumstances.
5. Subtract tax already collected or paid through other routes.
6. Add any likely balancing payment and Payments on Account shown by the current statement.
7. Divide the forward reserve by the months before the next due date.

If income varies, do not wait until the end of the year. Transfer a percentage of each customer payment into the reserve, then reconcile the percentage against actual profit every quarter. A monthly reserve is a planning discipline, not a fixed legal rate.

Worked illustration: stable profit

Suppose a sole trader estimates £36,000 of annual taxable profit and has no PAYE income, no Capital Gains Tax and no previous Payments on Account. The calculator may estimate a Self Assessment liability, but the actual result depends on the tax year, expenses, pension contributions and National Insurance rules.

If the estimated liability were £6,000 for illustration, the first January bill could include:

• £6,000 for the year being filed; and
• £3,000 as the first Payment on Account for the next year.

The July payment could then be another £3,000, subject to the official statement. This does not mean the next year’s final liability is exactly £6,000. If profit rises, a balancing payment can follow; if profit falls, the final position can be lower and the taxpayer may be able to claim a refund or reduce instalments under the rules.

The example shows the cash-flow shape, not a personal tax answer. Do not copy the £6,000 assumption into a return or use it as a universal percentage.

Variable income and seasonal businesses

Seasonal income creates a different reserve problem. A business may receive most invoices in summer but face the January payment when winter cash flow is weak. The reserve should follow taxable profit and payment timing, not only monthly turnover.

For variable income:

• keep a separate reserve from the operating account;
• transfer money when paid, not when invoiced if cash receipts are irregular;
• update the expected annual profit every quarter;
• model a low, base and high income year;
• keep VAT outside the personal Income Tax reserve;
• include unpaid invoices only according to the relevant tax and accounting method; and
• avoid withdrawing the reserve because one month was unusually strong.

A low month does not necessarily justify reducing the reserve. The previous-year statement may still require the same Payment on Account unless a formal reduction is made.

When Payments on Account may be reduced

GOV.UK says that if you know the tax owed will be lower than last year, you can ask HMRC to reduce Payments on Account online or by post using form SA303. This can help when profit has genuinely fallen, the business stopped, employment tax now covers more income, or a one-off source of income will not recur.

The decision must be evidence-led. If the reduction is too low and the final bill is higher, GOV.UK states that interest can be charged on the difference. A reduction is not a way to postpone an amount you already know is due. Keep the forecast, profit records and reason for the request.

Use three cases before reducing:

If the reduction only works in the optimistic case, preserve the reserve instead of relying on it.

Penalties, interest and reserve protection

The reserve does not replace filing on time or paying on time. GOV.UK publishes separate Self Assessment penalties guidance. Late filing, late payment and interest are separate issues, and the amount can depend on the notice, delay, tax type and circumstances.

Protect the reserve operationally:

• use a separate savings account or ledger category;
• label each transfer with the tax year;
• keep payment confirmations and HMRC statements;
• reconcile the reserve after every return;
• check the bank payment reference before sending money; and
• retain enough cash for the next instalment after making January’s payment.

Do not treat a tax reserve as available spending money. If the account is used for business expenses, record the withdrawal and replace it immediately. A reserve that exists only in a spreadsheet does not pay an HMRC bill.

Sole trader, landlord and mixed-income differences

A sole trader’s reserve is usually driven by trading profit and other personal income. A landlord may have property income, mortgage-interest restrictions, repairs, finance costs and different record requirements. An employee with a side hustle may have PAYE collecting some tax while the self-employed income creates a Self Assessment liability and possibly Payments on Account.

Mixed income can also affect the £1,000 and 80% Payments on Account exceptions. Do not decide that no instalment is due based on self-employed profit alone. The Self Assessment statement and HMRC’s calculation use the wider tax position.

If you operate through a limited company, separate personal extraction from the company’s tax reserve. Salary, dividends, Corporation Tax, PAYE and VAT can have different deadlines and legal payers. A personal Tax Reserve Assistant result is not a Corporation Tax calculation.

Making Tax Digital and future changes

Digital reporting and payment policy can change the timing of records or tax collection. A current proposal or future reform should not be treated as an immediate change to the 2026/27 payment dates unless HMRC has published the applicable rule. Continue to follow the current return, statement and payment instructions for the tax year being filed.

Keep bookkeeping records in a form that can support the return. The reserve is only as good as the profit estimate behind it. If income, expenses or the reporting route changes, update the model rather than carrying forward last year’s percentage without review.

Practical reserve process

Frequently Asked Questions

Run the scenario in the Tax Reserve Assistant, then compare it with the Self Assessment Deadlines guide, Payments on Account guide, Side Hustle Tax guide and Sole Trader Expenses guide. Confirm the final amount through your HMRC Self Assessment statement.

Official sources

• GOV.UK — Payments on account
• GOV.UK — Pay your Self Assessment tax bill
• GOV.UK — Self Assessment deadlines
• GOV.UK — Self Assessment penalties
• GOV.UK — Rates and thresholds for employers 2026 to 2027
• GOV.UK — Check your Income Tax for the current year