Can I be both PAYE and Self Assessment in the same year?

Yes, and it is one of the most common SA scenarios. If you have a main PAYE job and any untaxed income on the side - freelance work, rental income, dividends above £500, foreign income, capital gains over £3,000 - you file a Self Assessment alongside being a PAYE employee. The SA return reconciles the lot: it picks up the P60 figures from your employer (already taxed at source), adds the untaxed income, calculates the marginal tax due on the top slice, and bills the difference. You do not pay tax twice on the PAYE income - the return credits the PAYE deducted against your total bill.

Do I need to file SA for £500 of side income?

Generally no. HMRC's £1,000 trading allowance means the first £1,000 of self-employment income is tax-free and requires no return at all. Same for the £1,000 property allowance on rental income. If your side income from a single category sits below £1,000 gross, you do not need to register for SA or file a return. Above £1,000 you must register by 5 October following the tax year and file by 31 January. The thresholds are gross income, not profit - £600 of dog-walking income with £400 of expenses still falls under the allowance because gross is below £1,000.

What happens if I miss the 31 January deadline?

An automatic £100 penalty is issued the day after the deadline even if you owe no tax. After 3 months HMRC adds £10 a day up to £900. After 6 months a further 5% of the tax due or £300 (whichever is greater) is added. After 12 months another 5% or £300. Late payment is charged separately: 5% of the unpaid tax at 30 days, 6 months and 12 months, plus daily interest at the Bank of England base rate plus 2.5%. If you cannot pay, contact HMRC to set up a Time to Pay arrangement - the late-filing penalty still applies but late-payment penalties pause while the agreement runs.

Why do I owe more tax via SA when I am already taxed via PAYE?

Because the SA bill is calculated at your marginal rate, not the average rate. Side income stacks on top of your PAYE salary, so a £45k PAYE employee adding £8k of freelance income pays 40% Income Tax plus 6% Class 4 NI on the slice above £50,270 - even though their PAYE was deducted at the 20% basic rate during the year. The PAYE figures from your P60 are credited against the SA total, but the top-slice marginal tax is the headline charge. This is the single biggest source of first-year SA shock: the bill is not 20% of side income, it is closer to 46% of the slice that breaches the higher-rate threshold.

Can I claim work-from-home expenses without doing full SA?

For PAYE employees with no other untaxed income, yes - HMRC's online microservice at gov.uk/tax-relief-for-employees lets you claim the flat £6/week working-from-home allowance, professional subscriptions, uniform laundering and mileage on your own car for work journeys, all without filing a full SA return. The claim adjusts your tax code so the relief comes through your monthly PAYE for the rest of the year. Full SA is only required if you want to claim actual costs above the flat-rate allowance (which needs receipts and apportionment) or if you have other untaxed income that triggers SA anyway.

How do payments on account work?

If your SA bill is over £1,000 and less than 80% of your tax was deducted at source (so this almost always applies to anyone with material side income), HMRC requires you to pre-pay next year's tax in two instalments: 50% on 31 January (alongside the balancing payment for the year just ended) and 50% on 31 July. The first SA return you file therefore often produces a January bill that is 150% of the actual tax owed - the prior year balancing payment plus the first payment on account for the next year. The second instalment lands 6 months later. The system catches a lot of first-time filers off guard; budget for it before you spend the refund-shaped figure on your initial calculation.

What is the difference between SA and Making Tax Digital (MTD ITSA)?

Self Assessment is the existing annual paper / online return that has been HMRC's framework since 1997. Making Tax Digital for Income Tax Self Assessment (MTD ITSA) replaces it for self-employed and landlord taxpayers above certain income thresholds, with a phased rollout: 6 April 2026 for combined business / property income over £50,000, 6 April 2027 for over £30,000, and a planned (but unscheduled) extension to over £20,000. MTD ITSA requires quarterly digital updates through HMRC-recognised software plus a final declaration at year end, instead of one annual SA return. PAYE-only employees with no untaxed income are not affected. See our MTD ITSA 2026 guide for the phased thresholds and software-vendor landscape.

How do I claim a PAYE refund without filing Self Assessment?

Three routes depending on the trigger. If you left a job partway through the tax year and have not started a new one, file form P50 (Claim for repayment of tax) 4 weeks after stopping work. If you left the UK to live abroad permanently, file form P85. If you were on the wrong tax code for part of the year and still in PAYE employment, log into Personal Tax Account at gov.uk/personal-tax-account, check the current code on file, and request a refund through the online "claim a tax refund" service. PAYE refunds for incorrect codes usually arrive within 6 weeks of the request. None of these require an SA return - SA is only needed if you have untaxed income beyond the £1,000 allowances.

UK PAYE vs Self Assessment 2026/27

Most UK taxpayers pay Income Tax via PAYE - the employer deducts Income Tax and National Insurance from each payslip and remits it to HMRC before the net pay lands in your account. Roughly 12 million people on top of that also need to file a Self Assessment return because they have income that does not pass through a payroll: self-employment, property rentals, dividends, foreign income, capital gains, or earnings over £150,000 from any source. The two systems are not alternatives - they operate side by side, and most SA filers are also PAYE employees. This page explains how each system works, who must (and who can voluntarily) file an SA return, the filing and payment deadlines, the payments-on-account mechanism that ambushes first-year filers, and a worked example on the most common joint scenario: a salaried employee with a side income.

PAYE: how the deductions actually work

Pay As You Earn is the UK's withholding system for employment income. Your employer runs payroll software (or outsources it) that calculates your Income Tax and Class 1 National Insurance every time you are paid - weekly, fortnightly, four-weekly or monthly - using your tax code, which HMRC sets and updates. The employer pays the tax and NI directly to HMRC by the 22nd of the following month (19th for paper remittance) under Real Time Information (RTI), the same-day reporting framework mandatory since April 2013.

Your tax code is the operative lever. A code like 1257L tells the employer to apply £12,570 of tax-free Personal Allowance across the year (roughly £1,047.50 per month) and tax everything above that at the appropriate band rate. If your circumstances change - you start receiving rental income, you claim Marriage Allowance, you owe underpayment from a prior year, you switch jobs and end up on emergency code 1257L W1 - HMRC adjusts the code mid-year and the next payslip recalibrates the deductions. By the end of the tax year (5 April) the cumulative PAYE deductions should match the total tax due on your employment income, give or take a few pounds; if not, HMRC sends a P800 calculation showing the under or overpayment.

PAYE handles the majority of the population without anyone filing anything. If you have one job, no untaxed income, no taxable benefits in kind beyond what your employer already reports on P11D, and no claims to make beyond the standard allowances, you will never touch Self Assessment. The system reconciles itself.

Self Assessment: the annual reconciliation return

Self Assessment is the framework for declaring income that does not come through a payroll. You register with HMRC, receive a 10-digit Unique Taxpayer Reference (UTR), file an annual return covering the tax year ending 5 April, and pay any tax due by the deadlines below. The return covers everything: employment income (copied across from your P60), self-employment profits, rental income, dividends, savings interest, capital gains, pension contributions for higher-rate relief, charity donations under Gift Aid for the higher-rate top-up, foreign income, and any other taxable receipt that did not pass through PAYE.

The output of the return is a total tax liability for the year. Any tax you have already paid via PAYE (shown on your P60), CIS deductions (if you are a subcontractor in construction), or non-resident landlord scheme deductions is credited against the total. What remains is the SA balancing payment, due on 31 January following the end of the tax year. So your 2025-26 SA return (covering 6 April 2025 to 5 April 2026) must be filed and paid by 31 January 2027.

Who must file Self Assessment

You are required to file an SA return for 2026/27 if any of the following apply during the tax year:

Self-employment over £1,000 gross. The trading allowance covers the first £1,000 of gross self-employment income; above that you must register and file.
Property income over £1,000 gross. The property allowance is the rental equivalent of the trading allowance. Income from a single furnished room can also qualify for the £7,500 Rent a Room scheme separately.
Dividends over £500. The Dividend Allowance was cut from £2,000 (2022-23) to £1,000 (2023-24) to £500 (2024-25 onwards). Any dividend income above £500 must be declared via SA, even if you are otherwise a PAYE employee.
Total income over £150,000 from any source - PAYE, self-employment, dividends, rental - triggers automatic SA. HMRC removed the £100k threshold from April 2023.
High Income Child Benefit Charge (HICBC). If your or your partner's adjusted net income exceeds £60,000 and either of you claims Child Benefit, the higher earner owes 1% of the benefit for every £200 of income over £60,000, tapering to 100% at £80,000. HICBC is collected through SA - PAYE codes can be adjusted to spread it but the return is still required.
Foreign income. Any income from outside the UK - rental from an overseas property, foreign pension, work performed abroad - must be declared. Double-taxation relief is claimed via the SA foreign pages.
Capital gains over £3,000. The CGT annual exempt amount fell from £12,300 (2022-23) to £6,000 (2023-24) to £3,000 (2024-25 onwards). Disposals above the AEA must be reported - some via the dedicated UK Property Disposal service (residential property, within 60 days), others on the annual SA return.
Partnership profits. Each partner files their own SA covering their share of partnership profits, and the partnership itself files a separate SA800 return.
Untaxed savings interest over £10,000 (over the Personal Savings Allowance of £1,000 basic / £500 higher / £0 additional rate plus the £5,000 starting savings rate band for low earners). Below that, HMRC normally adjusts the tax code instead of requiring a return.
Trustees and executors dealing with estate or trust income.

Who can opt INTO Self Assessment voluntarily

Some PAYE-only employees benefit from filing an SA return even though HMRC does not require it. The most common reasons:

Higher-rate pension relief. Personal pension contributions get 20% basic-rate relief at source from the provider. Higher-rate (40%) and additional-rate (45%) taxpayers must claim the extra 20% or 25% via SA, unless their PAYE code is already adjusted for the relief.
Higher-rate Gift Aid relief. Same mechanism as pensions - the charity claims 25% basic-rate top-up at source; the donor reclaims the higher-rate or additional-rate difference via SA.
EIS, SEIS, VCT investment relief. Enterprise Investment Scheme (30% income tax credit, £1m annual limit), Seed EIS (50%, £200k limit) and Venture Capital Trust subscriptions (30%, £200k limit) all require an SA return to claim the income tax credit. Loss relief on a failed EIS or SEIS company also goes through SA.
Work-from-home expense claims above the flat rate. The £6/week flat rate can be claimed through the gov.uk microservice without SA. Claiming actual proportioned utility bills (which is rarely worth the bookkeeping) requires SA.
Mileage relief above the AMAP rate. If your employer pays under HMRC's Approved Mileage Allowance Payment rates (45p for the first 10,000 miles, 25p above), you can claim the difference. Up to £2,500 of unreimbursed expenses can be claimed via P87 / online service without SA; above that, SA is required.
Foreign tax credit on an asset. If you sold an overseas asset and paid foreign capital gains tax, you reclaim the UK side of the double-taxation relief via SA.

Filing and payment deadlines

The Self Assessment year ends on 5 April. Everything below relates to the return for the tax year ending on the previous 5 April - so for 2026/27 (tax year ending 5 April 2027), the deadlines fall through 2027 and 2028.

5 October following the tax year end - register for SA if you are filing for the first time. Late registration is a separate penalty regime; HMRC needs time to issue the UTR before you can file.
31 October - paper SA return filing deadline. Almost no one files on paper any more, but if you do, this is the date.
30 December - online filing deadline if you want HMRC to collect tax owed under £3,000 through your PAYE code over the next tax year (coded out via a tax code adjustment). After this date you cannot opt for collection through PAYE.
31 January - online SA filing deadline AND payment deadline for the balancing payment for the prior year AND the first payment on account for the current year.
31 July - second payment on account for the current tax year.

Payments on account: why first-year SA shocks people

Payments on account are HMRC's mechanism for pulling forward next year's tax. They apply when your SA bill (after PAYE and other deductions at source) exceeds £1,000 AND less than 80% of your tax was deducted at source. For anyone with material self-employment or rental income alongside PAYE, both conditions are virtually always met.

The mechanism: HMRC estimates that next year's tax will be the same as this year's, and asks for it in two equal half-year instalments. So on 31 January you pay (a) the balancing payment for the year just ended, plus (b) 50% of the estimated tax for the year currently in progress. On 31 July you pay (c) the other 50% of the current year. Then the following 31 January you pay any balancing payment if the actual figure exceeded the estimate, plus the first payment on account for the new year. And so on.

For a first-year filer this lands as a January bill that is effectively 150% of the actual tax owed - the balancing payment for last year (100%) plus the first payment on account for next year (50%). It is mathematically fair (you eventually pay one year's tax per year) but it ambushes people who treated their initial SA calculation as the figure they owed. Budget for it. If your income is genuinely lower this year than last, you can apply to reduce payments on account using form SA303 or the equivalent online process - but if HMRC later finds your actual liability exceeded the reduced figure, interest is charged from the original due dates.

PAYE refund mechanics (without filing SA)

If you have overpaid PAYE and no SA filing requirement, three paths reclaim the money without registering for SA:

Form P50 - "Claim for repayment of tax when you have stopped working". Filed 4 weeks after stopping work, claims back the overpayment caused by the tax code spreading your Personal Allowance evenly across a year you only worked part of.
Form P85 - "Leaving the UK - getting your tax right". Filed when you leave the UK permanently or for at least a full tax year, claims back the overpaid tax on the partial-year employment income.
Personal Tax Account online refund - gov.uk/personal-tax-account. For any other PAYE reconciliation - wrong tax code part-year, untaxed allowances, marriage allowance backdated. HMRC checks the figures and issues a refund directly to your bank account, usually within 6 weeks.

None of these require an SA return. SA is only triggered when untaxed income exists beyond the £1,000 trading and property allowances, or when one of the other triggers above applies.

Joint PAYE plus SA situations

The majority of SA filers are also PAYE employees. The most common joint scenarios:

High earner with a side income. £45-90k PAYE salary, £5-20k of freelance or consulting on top. The SA bill is the marginal tax on the side income stacked above the PAYE. Higher-rate 40% Income Tax + 6% Class 4 NI typically applies to most of the side income, so the SA bill is roughly 46% of the side gross profit.
Inside-IR35 contractor with dividend income from a dormant Ltd. The umbrella pays full PAYE on the day rate; the prior Ltd holds retained profits that the contractor distributes as dividends to use the £500 allowance and basic-rate dividend band. SA reconciles both streams.
PAYE employee with a rental property. The rental income net of allowable expenses is stacked above the PAYE salary, taxed at the marginal rate. Mortgage interest is restricted to a 20% basic-rate credit since April 2020 (Section 24).
HICBC at £60-80k. The household claims Child Benefit; the higher earner is on £60-80k PAYE; the HICBC tapers from 0% to 100% over the £20,000 band. SA reconciles the charge.
PAYE employee with foreign dividend or pension income. Foreign income must be declared on SA even if foreign tax has already been deducted; the SA return applies the double-taxation treaty relief to avoid double tax.

Penalty regime

Late filing. £100 fixed penalty the day after the deadline, regardless of tax owed. £10 a day from 3 months late, capped at £900. £300 or 5% of tax due (whichever is greater) at 6 months. Another £300 or 5% at 12 months.
Late payment. 5% of the unpaid tax at 30 days, 6 months and 12 months. Daily interest at Bank of England base rate plus 2.5% (the current effective late-payment interest rate is published quarterly at gov.uk).
Inaccuracy. 0-30% of the lost tax for careless errors, 20-70% for deliberate, 30-100% for deliberate and concealed. Voluntary disclosure significantly reduces the penalty.
Failure to notify chargeability. Separate penalty for not registering for SA when required - up to 100% of the unpaid tax in serious cases.

Worked example: £45,000 PAYE + £8,000 freelance (2026/27)

Take a typical joint scenario: a permanent employee earning £45,000 PAYE plus £8,000 of freelance design work on the side. The PAYE side is handled by the employer automatically; Income Tax and Class 1 NI are deducted from each payslip and arrive at HMRC under RTI. By the end of the year the P60 shows what was deducted - roughly the expected basic-rate tax on the £45k.

The £8,000 freelance income is the SA-triggering bit. It is stacked on top of the £45,000 PAYE income for marginal-rate purposes. The Personal Allowance and basic-rate band are already used up by the PAYE income, so most of the £8k breaches the higher-rate threshold of £50,270. Income Tax on that slice is 40%; Class 4 NI is 6% on profits between £12,570 and £50,270, then 2% above. Computed by the same engine that drives the self-employed calculator:

Component	Amount
PAYE salary (handled by employer)	£45,000
Freelance gross profit (SA-reportable)	£8,000
Combined income for marginal-rate purposes	£53,000
Income Tax on side income (marginal slice)	£2,146
Class 4 NI on side income (marginal slice)	£371
SA balancing payment due (31 January)	£2,517
Effective rate on freelance income	31.5%

The headline figure is the effective rate: 31.5% of the £8,000 side income disappears to HMRC because it stacks above the higher-rate threshold. The employee did not pay 20% on the side income (their average rate). They paid the marginal rate, which is much higher. On top of that, if the SA bill exceeds £1,000, the same £8k worth of marginal tax becomes a payment-on-account driver: 50% pre-paid in the following January, 50% in July. The first January SA payment under this scenario can run to £3,775 - the £2,517 balancing payment plus the £1,258 first payment on account.

Do you need to file SA? Decision tree

Was your total income over £150,000? If yes, you must file SA. If no, continue.
Did you have self-employment or freelance income over £1,000 gross? If yes, file SA. If no, continue.
Did you receive rental income over £1,000 gross? If yes, file SA. If no, continue.
Did you receive dividends over £500? If yes, file SA. If no, continue.
Did you or your partner claim Child Benefit with either income over £60,000? If yes, the higher earner files SA for HICBC. If no, continue.
Did you have foreign income, capital gains over £3,000, or partnership profits? If yes, file SA. If no, continue.
Did you want to claim higher-rate relief on pension contributions, Gift Aid, or EIS / SEIS / VCT investments? If yes, voluntary SA is the path. If no - you are PAYE-only and do not need to file.

Frequently asked questions

Can I be both PAYE and Self Assessment in the same year?: Yes, and it is one of the most common SA scenarios. If you have a main PAYE job and any untaxed income on the side - freelance work, rental income, dividends above £500, foreign income, capital gains over £3,000 - you file a Self Assessment alongside being a PAYE employee. The SA return reconciles the lot: it picks up the P60 figures from your employer (already taxed at source), adds the untaxed income, calculates the marginal tax due on the top slice, and bills the difference. You do not pay tax twice on the PAYE income - the return credits the PAYE deducted against your total bill.
Do I need to file SA for £500 of side income?: Generally no. HMRC's £1,000 trading allowance means the first £1,000 of self-employment income is tax-free and requires no return at all. Same for the £1,000 property allowance on rental income. If your side income from a single category sits below £1,000 gross, you do not need to register for SA or file a return. Above £1,000 you must register by 5 October following the tax year and file by 31 January. The thresholds are gross income, not profit - £600 of dog-walking income with £400 of expenses still falls under the allowance because gross is below £1,000.
What happens if I miss the 31 January deadline?: An automatic £100 penalty is issued the day after the deadline even if you owe no tax. After 3 months HMRC adds £10 a day up to £900. After 6 months a further 5% of the tax due or £300 (whichever is greater) is added. After 12 months another 5% or £300. Late payment is charged separately: 5% of the unpaid tax at 30 days, 6 months and 12 months, plus daily interest at the Bank of England base rate plus 2.5%. If you cannot pay, contact HMRC to set up a Time to Pay arrangement - the late-filing penalty still applies but late-payment penalties pause while the agreement runs.
Why do I owe more tax via SA when I am already taxed via PAYE?: Because the SA bill is calculated at your marginal rate, not the average rate. Side income stacks on top of your PAYE salary, so a £45k PAYE employee adding £8k of freelance income pays 40% Income Tax plus 6% Class 4 NI on the slice above £50,270 - even though their PAYE was deducted at the 20% basic rate during the year. The PAYE figures from your P60 are credited against the SA total, but the top-slice marginal tax is the headline charge. This is the single biggest source of first-year SA shock: the bill is not 20% of side income, it is closer to 46% of the slice that breaches the higher-rate threshold.
Can I claim work-from-home expenses without doing full SA?: For PAYE employees with no other untaxed income, yes - HMRC's online microservice at gov.uk/tax-relief-for-employees lets you claim the flat £6/week working-from-home allowance, professional subscriptions, uniform laundering and mileage on your own car for work journeys, all without filing a full SA return. The claim adjusts your tax code so the relief comes through your monthly PAYE for the rest of the year. Full SA is only required if you want to claim actual costs above the flat-rate allowance (which needs receipts and apportionment) or if you have other untaxed income that triggers SA anyway.
How do payments on account work?: If your SA bill is over £1,000 and less than 80% of your tax was deducted at source (so this almost always applies to anyone with material side income), HMRC requires you to pre-pay next year's tax in two instalments: 50% on 31 January (alongside the balancing payment for the year just ended) and 50% on 31 July. The first SA return you file therefore often produces a January bill that is 150% of the actual tax owed - the prior year balancing payment plus the first payment on account for the next year. The second instalment lands 6 months later. The system catches a lot of first-time filers off guard; budget for it before you spend the refund-shaped figure on your initial calculation.
What is the difference between SA and Making Tax Digital (MTD ITSA)?: Self Assessment is the existing annual paper / online return that has been HMRC's framework since 1997. Making Tax Digital for Income Tax Self Assessment (MTD ITSA) replaces it for self-employed and landlord taxpayers above certain income thresholds, with a phased rollout: 6 April 2026 for combined business / property income over £50,000, 6 April 2027 for over £30,000, and a planned (but unscheduled) extension to over £20,000. MTD ITSA requires quarterly digital updates through HMRC-recognised software plus a final declaration at year end, instead of one annual SA return. PAYE-only employees with no untaxed income are not affected. See our MTD ITSA 2026 guide for the phased thresholds and software-vendor landscape.
How do I claim a PAYE refund without filing Self Assessment?: Three routes depending on the trigger. If you left a job partway through the tax year and have not started a new one, file form P50 (Claim for repayment of tax) 4 weeks after stopping work. If you left the UK to live abroad permanently, file form P85. If you were on the wrong tax code for part of the year and still in PAYE employment, log into Personal Tax Account at gov.uk/personal-tax-account, check the current code on file, and request a refund through the online "claim a tax refund" service. PAYE refunds for incorrect codes usually arrive within 6 weeks of the request. None of these require an SA return - SA is only needed if you have untaxed income beyond the £1,000 allowances.