Self-Assessment Tax Return Checklist UK: The Complete SA100 Audit Guide

Employment and Directorships (SA102 Supplementary Schedule)

Every employment held during the tax year requires separate disclosure:

• Form P60 (End of Year Certificate): Enter total taxable pay and total PAYE tax deducted from Box 1 and Box 2.
• Form P45 (Details of Employee Leaving Work): If you left an employer during the tax year, enter figures from Part 1A.
• Form P11D (Expenses and Benefits): Statutory benefits in kind under ITEPA 2003 (company cars, private medical insurance, employer-provided accommodation, beneficial loans).
• Redundancy & Termination Settlements: Ensure the £30,000 statutory exemption under Section 401 ITEPA 2003 is correctly applied; PILON (Pay in Lieu of Notice) is fully taxable.

Sole Trader and Partnership Profits (SA103 Schedule)

Self-employment income must be declared on either the SA103S (short form for turnover under £90,000) or SA103F (full form):

• Gross Business Turnover: Total invoices, merchant gateway receipts, and client fees invoiced (accruals basis) or received (cash basis). Note that the cash basis is the statutory default.
• Trading Allowance vs Actual Expenses: If your allowable expenses are under £1,000, claim the flat £1,000 statutory allowance under Section 23ZB ITTOIA 2005. You cannot claim both actual expenses and the allowance.
• Construction Industry Scheme (CIS) Deductions: Collect all monthly CIS deduction statements from principal contractors. Reconcile total gross payments, material costs, and tax withheld at 20% or 30% to ensure full tax credit offset on your final SA100 calculation.

Property and Rental Receipts (SA105 Schedule)

Residential and commercial property income must be reported under UK property rules:

• Rental Income & Tenant Fees: Total gross rents collected across all properties during the tax year.
• Property Allowance (£1,000): Can be elected instead of actual repairs, insurance, and management fees if allowable costs are below £1,000.
• Section 24 Mortgage Finance Restriction: Under Section 24 ITTOIA 2005, residential mortgage interest and finance fees are not deductible expenses against rental profit. Instead, declare finance costs in Box 44 to claim a 20% basic rate tax credit deduction.

Dividends, Company Distributions and Investment Income

Declared on the core SA100 return (Page TR3):

• Dividend Counterfoils / Vouchers: Company director distributions and equity portfolio dividends. The Dividend Nil Rate is £500; dividends above this are taxed at 10.75% (Basic), 35.75% (Higher), and 39.35% (Additional).
• Bank & Building Society Interest: Annual tax interest certificates detailing gross untaxed interest. The Personal Savings Allowance (PSA) is £1,000 for Basic Rate taxpayers, £500 for Higher Rate taxpayers, and £0 for Additional Rate taxpayers.
• Exempt Assets (Do Not Report): Income earned within ISAs (Cash or Stocks & Shares) and NS&I Premium Bonds prizes are 100% tax-free and must never be entered on your SA100 return.

Capital Gains and Digital Assets (SA108 Schedule)

Disposals of property, cryptoassets, unlisted shares, and valuable chattels:

• Annual Exempt Amount: Capital gains are tax-free up to £3,000 per individual. Net gains above £3,000 are subject to Capital Gains Tax under the Taxation of Chargeable Gains Act 1992 (TCGA 1992).
• 60-Day UK Residential Property Returns: If you sold a UK residential property that was not fully covered by Private Residence Relief (PRR), you must have submitted a 60-day digital return and paid advance CGT. Enter these figures on the SA108 to reconcile final tax.

Pension Tax Relief: Net-Pay vs Relief at Source (RAS)

The golden rule of UK pension tax reporting:

• Net-Pay Arrangements (Section 193 Finance Act 2004): Used in most traditional workplace occupational schemes. Contributions are deducted directly from your gross salary before PAYE tax is calculated. Do not enter these contributions on your SA100 return, as you have already received 100% of your tax relief through your payslip.
• Relief at Source (RAS) Schemes (SIPP & Personal Pensions): Contributions are paid from your net bank account. The scheme provider automatically claims 20% basic rate relief from HMRC (e.g. you deposit £800, and the provider adds £200 to credit £1,000 into your pension fund).

SIPP and Personal Pension Higher Rate Tax Reclaim

If you are a Higher Rate (40%) or Additional Rate (45%) taxpayer (or 42%/45%/48% in Scotland), you must declare your Relief at Source contributions on Page TR4 (Box 1) of the SA100. Enter the grossed-up contribution (£1,000 in the example above). HMRC recalculates your tax computation by expanding your Basic Rate tax band by £1,000, delivering an extra £200 (for 40% taxpayers) or £250 (for 45% taxpayers) in reduced tax or cash rebate.

Gift Aid Declarations (Finance Act 2004 s.414)

Donations made under Gift Aid allow charities to reclaim 20% basic tax relief. Higher-rate and additional-rate taxpayers can reclaim the difference on their SA100. Enter the net donations grossed up by 100/80 (e.g. an £80 donation is entered as £100 gross). This expands your basic rate band, reducing your higher-rate tax liability by 20% (£20) of the gross donation.

Marriage Allowance Transfer (ITA 2007 s.55A)

Under Section 55A of the Income Tax Act 2007, an individual earning below the £12,570 Personal Allowance can transfer 10% (£1,260) of their allowance to their civil partner or spouse, provided the recipient pays tax at the 20% Basic Rate. This saves up to £252 per tax year. Ensure this election is active or confirmed on your SA100 return.

The Three Critical Filing and Payment Deadlines