How to Read Your HMRC Tax Calculation

You have filed your Self Assessment tax return. A few days later, HMRC sends you a tax calculation — the SA302. You open it expecting clarity. Instead, you are confronted with a page of figures, boxes, references to "payments on account," and a total that seems far higher than anything you were expecting. You close the document, pour a strong cup of tea, and wonder whether you should just pay it and hope for the best.

This is an extremely common experience. The SA302 tax calculation is not particularly intuitive, and HMRC's terminology can be confusing if you are not an accountant. But the document is actually quite logical once you understand what each section means and why the numbers are what they are.

In this guide, we will walk through the SA302 section by section, explain the most common points of confusion (especially the dreaded payments on account), and show you how to cross-reference the figures with your own records to make sure everything is correct.

What the SA302 Tax Calculation Shows

The SA302 is HMRC's official calculation of your tax liability for a given tax year. It takes the figures you submitted on your Self Assessment return — your income, expenses, and any reliefs or allowances — and applies the current tax rates and thresholds to calculate what you owe (or, occasionally, what HMRC owes you).

You can view your SA302 online through your HMRC personal tax account, or you can request a paper copy by calling HMRC. Your accountant or mortgage lender may also ask for a copy, as it serves as official proof of your income and tax position.

The SA302 is divided into several sections, and understanding each one is the key to understanding the whole document.

Section 1: Income

This section lists all the income you reported on your tax return, broken down by source:

• Self-employment income. Your net profit (turnover minus allowable expenses) from your sole trader business.
• Employment income. If you also have a job, your gross salary and any benefits in kind.
• Rental income. Net rental profit from any properties you let.
• Savings and investment income. Interest from bank accounts, dividends from shares, etc.
• Other income. Any income that does not fit the categories above — for example, freelance income that is not from a registered trade, or income from overseas.

Each income source shows the gross figure before any deductions. The total at the bottom of this section is your total income for the year.

What to check: Make sure every income figure matches what you reported on your tax return. If you see a figure you do not recognise, it may be because HMRC has received information from a third party (such as your employer or bank) that does not match your return. This is worth investigating promptly.

Section 2: Allowances and Deductions

This section shows the amounts that are subtracted from your total income before tax is calculated:

• Personal Allowance. The standard Personal Allowance for 2025/26 is £12,570. This is the amount of income you can earn tax-free. However, if your total income exceeds £100,000, your Personal Allowance is reduced by £1 for every £2 of income above that threshold, reaching zero at £125,140.
• Blind person's allowance. An additional allowance if you are registered blind.
• Gift Aid donations. As discussed in our guide on charitable donations, your Gift Aid donations can extend your basic rate band, reducing the amount of income taxed at higher rates.
• Pension contributions. Gross pension contributions reduce your taxable income.
• Other reliefs. This might include losses brought forward from a previous year, the Marriage Allowance transfer, or other specific reliefs.

The result after subtracting allowances and deductions from total income is your taxable income — the amount on which tax is actually charged.

What to check: Confirm that your Personal Allowance is correct. If it has been reduced (because your income exceeds £100,000), verify the reduction calculation. Also check that any pension contributions and Gift Aid donations you claimed are reflected here.

Section 3: Tax Charged

This is where the actual tax calculation happens. Your taxable income is split into bands, and each band is taxed at the appropriate rate:

| Band (2025/26) | Rate | |---|---| | £0 – £37,700 (basic rate) | 20% | | £37,701 – £125,140 (higher rate) | 40% | | Over £125,140 (additional rate) | 45% |

Note that these bands apply to taxable income (after the Personal Allowance has been deducted). So a sole trader with total income of £60,000 has taxable income of £47,430 (£60,000 minus the £12,570 Personal Allowance), of which £37,700 is taxed at 20% and £9,730 is taxed at 40%.

The tax charged section also includes:

• National Insurance contributions. Class 2 and Class 4 NICs for self-employed individuals. Class 2 is a flat weekly rate (£3.45 per week for 2025/26, if applicable). Class 4 is calculated as a percentage of your profits between the lower and upper profits limits.
• Student loan repayments. If you have an outstanding student loan, repayments are calculated as a percentage of your income above the relevant threshold.
• Tax on savings and dividends. These are taxed at different rates from earned income, and the SA302 shows them separately.

What to check: Verify that the correct tax bands have been applied. If you made Gift Aid donations, check that your basic rate band has been extended accordingly. Also verify the National Insurance calculations — the thresholds and rates change annually, and errors here are not uncommon.

Section 4: Tax Already Paid

This is the section that causes the most confusion and the most complaints.

The "tax already paid" figure includes:

• Tax deducted at source. If you have employment income, your employer will have deducted income tax through PAYE. This amount is credited against your total tax liability.
• Tax paid on savings interest. Some savings interest has tax deducted at source (though this is less common since the introduction of the Personal Savings Allowance).
• Payments on account already made. This is the big one. If your previous year's Self Assessment showed a tax liability above £1,000 (and less than 80% of your total tax was collected at source), HMRC will have required you to make payments on account — advance payments towards the current year's tax bill, each equal to half of the previous year's liability.

The total "tax already paid" is subtracted from the total "tax charged" to arrive at the amount you still owe — the balancing payment.

Why Your Bill Seems High: Payments on Account Explained

This is the number one source of confusion and frustration for sole traders. You file your return, expecting a bill for the current year's tax, and instead you receive a bill that seems nearly double what you expected.

Here is why.

When you file your first Self Assessment return (or any return that results in a tax liability over £1,000 that was not mostly collected at source), HMRC requires you to make payments on account for the following year. These are two advance payments, each equal to 50% of the current year's liability:

• First payment on account: Due 31 January (the same day as the balancing payment for the previous year).
• Second payment on account: Due 31 July.

So on 31 January, you are potentially paying three things at once:

1. The balancing payment for the tax year just ended (the difference between what you owe and what you have already paid through previous payments on account).
2. The first payment on account for the coming year (50% of the previous year's liability).
3. Any Class 2 National Insurance that is due.

For a sole trader whose business is growing, this can result in a January bill that is significantly larger than the actual tax on the year just ended.

Example:

• 2024/25 tax liability: £4,000 (first year of Self Assessment, no payments on account made)
• On 31 January 2026, you pay:
  • £4,000 balancing payment for 2024/25
  • £2,000 first payment on account for 2025/26 (50% of £4,000)
  • Total: £6,000
• On 31 July 2026, you pay:
  • £2,000 second payment on account for 2025/26

When you file your 2025/26 return, HMRC calculates your actual liability. If it turns out to be £5,000, and you have already paid £4,000 in payments on account, your balancing payment is just £1,000. But if your income has grown and the liability is £7,000, the balancing payment is £3,000 — plus the first payment on account for 2026/27 at £3,500 (50% of £7,000).

You can see how the January bill escalates quickly for a growing business. The payments on account system essentially means you are always paying part of next year's tax alongside the balance of the current year's tax.

Can you reduce payments on account? Yes. If you know your income will be lower in the current year than it was in the previous year, you can apply to reduce your payments on account through your HMRC online account. But be cautious — if your estimate is too low and you end up owing more, HMRC will charge interest on the underpayment.

For more on managing your Self Assessment obligations, including payments on account, see our guide on how to file your Self Assessment for 2026.

Cross-Referencing with Your Records

Once you understand the structure of the SA302, you should cross-reference the key figures with your own records. This is straightforward if your bookkeeping is up to date.

Income figures. Compare the self-employment income on the SA302 with the profit figure in your accounts. They should match exactly, because the SA302 is derived from the figures you submitted.

Expenses and deductions. If the income figure is correct but the tax seems wrong, check that your allowances and deductions have been applied correctly. A missing pension contribution or Gift Aid claim can make a significant difference.

Tax already paid. If you have employment income, check that the PAYE deducted matches your P60 or final payslip. If you made payments on account, verify that the amounts credited match what you actually paid.

National Insurance. Check the Class 4 NIC calculation against the published thresholds and rates. HMRC's calculation is usually correct, but it is worth verifying, especially in years when thresholds change.

If you find a discrepancy, do not panic. It could be a simple data entry error on your return, an HMRC processing error, or information from a third party that does not match your records. You can contact HMRC to query the calculation or, if necessary, amend your return.

Spotting Errors and When to Contact HMRC

Common errors to watch for on the SA302 include:

• Missing income sources. If you have income from multiple sources, make sure all of them are reflected. Sometimes an employment source is omitted because the employer submitted their information late.
• Incorrect Personal Allowance. If your allowance has been reduced unexpectedly, check whether HMRC has information about your income that you are not aware of — perhaps from a previous year's return or an employer's report.
• Duplicate income. In rare cases, HMRC may double-count income if they receive information from both your return and a third party. This is worth checking if your total income figure seems too high.
• Missing payments on account. If you made payments on account but they are not shown as "tax already paid," contact HMRC immediately. This could mean the payments were not allocated to the correct year.
• Wrong tax rates. With devolved tax rates in Scotland and potentially different thresholds, make sure the correct rates have been applied for your circumstances.

If you spot an error, you can:

1. Call HMRC on the Self Assessment helpline (0300 200 3310) to discuss the discrepancy.
2. Amend your return if the error was on your side. You can amend a Self Assessment return within 12 months of the original filing deadline.
3. Write to HMRC if the error is on their side, explaining the discrepancy and providing supporting evidence.

You can also check your tax position at any time through the HMRC income tax checker, which shows how your bill was calculated.

How Penny's Tax Estimates Compare to the Official Calculation

One of the most valuable features of Accounted is Penny's real-time tax estimate. Throughout the year, Penny calculates your estimated income tax and National Insurance liability based on the transactions recorded in your account. This estimate updates automatically as new income and expenses come in.

When your SA302 arrives, you can compare HMRC's calculation with Penny's estimate. In most cases, they should be very close — the small differences typically arise from timing (transactions that fell into a different period) or adjustments that HMRC applies automatically (such as the Marriage Allowance or a coding notice adjustment).

If there is a significant discrepancy — say, more than a few hundred pounds — it is worth investigating. The most common reasons are:

• Income you forgot to record in Accounted. Perhaps a cash payment or a foreign income source.
• Expenses that HMRC has queried or disallowed. This would usually be accompanied by a letter from HMRC.
• Payments on account. Penny's estimate shows your tax liability for the year. The SA302 shows the liability plus payments on account for the following year. This is the most common reason the SA302 total is higher than Penny's estimate.

Having Penny's estimate as a benchmark makes it much easier to spot genuine errors on the SA302, because you have an independent calculation to compare against.

To explore Penny's tax estimation and all of Accounted's features, visit the features page.

Requesting a Copy of Your SA302

You may need a copy of your SA302 for a mortgage application, a loan, or a visa application. There are several ways to obtain one:

• Online. Log into your HMRC personal tax account and navigate to the Self Assessment section. You can view and print your tax calculation for any year that is available.
• By phone. Call the Self Assessment helpline and request a copy to be posted to your registered address.
• Through your accountant. If you have an accountant who is registered as your agent with HMRC, they can access your SA302 through their agent account.
• Through your software. If you filed your return using Accounted, you can view the calculation directly in the app. Penny stores a copy of your submitted return and the corresponding tax calculation for easy reference.

Mortgage lenders typically require SA302s for the last two or three years, along with the corresponding tax year overviews (which show that you actually paid the tax). Make sure you can access both documents before starting a mortgage application.

Making Sense of It All

The SA302 is not designed to be user-friendly. It is designed to be comprehensive and accurate, which sometimes comes at the cost of clarity. But once you understand the structure — income, allowances, tax charged, tax already paid, and the amount due — it becomes a document you can read with confidence rather than dread.

The single most important thing to understand is payments on account. They are not a penalty, they are not a mistake, and they are not HMRC being unreasonable. They are an advance payment system designed to spread your tax bill across the year. Once you expect them and plan for them, the January bill stops being a shock.

Accounted and Penny help you stay ahead of all of this. With real-time tax estimates, you know your approximate liability throughout the year. With clear transaction records, you can verify every figure on the SA302. And with Penny's reminders, you never miss a payment deadline.

Start your free trial of Accounted and take the uncertainty out of your tax calculation.

Accounted files your Self Assessment directly to HMRC, with your return pre-populated from your records. See Self Assessment filing →