Self Assessment Tax Return Guide For A Sole Trader With Multiple Trades

Why Multiple Trades Changes Your Self Assessment Tax Return

If you run two separate businesses as a sole trader, your self assessment tax return is more complicated than the standard single-trade return. Most online guides assume you have one trade. They miss the specific box-by-box guidance you need when HMRC expects two separate SA103 self-employment pages.

This self assessment tax return guide covers exactly that scenario. Whether you are a freelance graphic designer who also runs an Etsy shop, a builder who also does property maintenance, or a consultant with a separate ecommerce business, the filing rules are the same.

You need one SA103S (short) or SA103F (full) page per trade. HMRC does not let you combine two trades into a single set of figures. Each trade has its own turnover, expenses, and profit calculation.

When Are Two Activities Separate Trades?

HMRC looks at several factors to decide whether you have one trade or two. The key test is whether the activities are genuinely separate in organisation, premises, customers, and management.

A plumber who also does general handyman work through the same website and van is probably running one trade. A plumber who also runs a separate catering business from a commercial kitchen is running two trades.

The sole trader and self employment guidance on our blog covers the distinction in more detail. If HMRC challenges your split, they will look at your accounting records, your marketing, and whether you keep separate bank accounts.

Which Self Assessment Forms You Need

For a standard self assessment tax return with multiple trades, you need:

• SA100 - the main tax return form (online or paper)
• SA103F (full) or SA103S (short) - one for each trade
• SA102 - employment pages (if you also have a job)

If you file online through HMRC's service or commercial software like Xero, FreeAgent, or QuickBooks, the system generates the correct pages automatically once you tell it you have multiple self-employment schedules.

Paper filers need to request extra SA103 pages from HMRC. The online system handles it more cleanly, which is one reason we recommend digital filing with Making Tax Digital compatible software.

Box-by-Box Guidance for Each Trade

Each SA103 page asks the same questions. You complete one for trade A, then a separate one for trade B. The boxes are identical. The figures are not.

Turnover (Box 10 to 14)

Box 10 asks for the total sales for that trade. Do not combine the two trades here. If trade A turned over £42,000 and trade B turned over £18,000, you enter £42,000 on the first SA103 and £18,000 on the second.

Box 11 covers any amounts not included in turnover that are still taxable (for example, lump sum compensation payments). This is rare for most sole traders.

Box 12 asks for adjustments to turnover. Common examples include VAT adjustments if you are VAT registered and using the flat rate scheme, or amounts received that relate to a different accounting period.

Box 13 is the net turnover after adjustments. Box 14 asks for the total of any amounts you received that are not part of your normal trade income but are still taxable. This might include a one-off grant or insurance payout.

Expenses (Box 15 to 30)

This is where multiple trades create the most confusion. You cannot lump all expenses together. Each trade has its own cost base.

Box 15 to 30 covers the standard expense categories: cost of sales, construction industry subcontractor costs (if applicable), wages and salaries, rent and rates, repairs, premises costs, motor expenses, travel and subsistence, advertising and marketing, telephone and internet, office costs, professional fees, bad debts, accountancy costs, financial charges, and other allowable expenses.

The critical point is allocation. If you have a single mobile phone contract used for both trades, you must apportion the cost between them on a reasonable basis. We typically see 50:50 splits, but you can use any fair method. Document your reasoning in your records.

If you have a van used for trade A only, the full motor expenses go on trade A's page. If you share a home office between both trades, apportion the household expenses (heat, light, broadband, council tax) between the two SA103 pages.

Box 31 is the total expenses for that trade. Box 32 is the net profit or loss (turnover minus expenses).

Capital Allowances (Box 33 to 41)

Capital allowances are claimed per trade. If you buy a laptop for trade A only, the Annual Investment Allowance (AIA) claim goes on trade A's page. If you buy equipment used across both trades, apportion the cost.

Each trade has its own AIA entitlement. The £1,000,000 annual limit applies per business, not per person. So trade A can claim up to £1M and trade B can claim up to £1M, provided each trade genuinely uses the assets.

Box 36 asks for the total AIA claimed. Box 37 covers other capital allowances (writing down allowances, first year allowances). Box 41 gives the total capital allowances for that trade.

Adjustments and Total Profit (Box 42 to 46)

Box 42 asks for any adjustments to arrive at the adjusted profit for the year. Common adjustments include disallowable expenses (client entertaining, depreciation, fines) that you added back in your accounts.

Box 43 is the adjusted profit after capital allowances. Box 44 is the loss brought forward from earlier years (only if this specific trade had an unrelieved loss). Box 45 is the total profit or loss for this trade.

Box 46 asks for the total of any overlap relief. This applies if you changed your accounting date in the past. Most sole traders leave this blank.

Combining the Results on Your SA100

Once each SA103 page shows its individual profit or loss, you transfer the totals to the main SA100 form. Box 5 on the SA100 asks for the total profit from all self-employment trades. You add trade A's profit and trade B's profit together.

If trade A made £24,000 and trade B made £6,000, you enter £30,000 in box 5. If one trade made a loss, you net it off. Trade A profit of £24,000 and trade B loss of £3,000 gives £21,000.

This combined figure then flows into your total income calculation alongside any employment income, dividends, property income, or other taxable receipts.

Class 4 National Insurance With Multiple Trades

Class 4 NIC is calculated on your combined self-employment profits. HMRC adds trade A and trade B profits together, then applies the Class 4 thresholds to the total.

For 2025/26, Class 4 NIC is 9% on profits between £12,570 and £50,270, and 2% on profits above £50,270. If trade A made £30,000 and trade B made £25,000, your combined £55,000 triggers Class 4 on the first £37,700 (from £12,571 to £50,270) at 9%, and the remaining £4,730 at 2%.

Class 2 NIC was abolished from April 2024 for most sole traders. You no longer need to pay a flat weekly amount. However, you may still need to pay voluntary Class 2 or Class 3 contributions to protect your state pension entitlement if your combined profits are low.

Common Mistakes With Multiple Trades

The most frequent error we see is combining expenses from both trades onto one SA103 page. This creates a mismatch with HMRC's records and can trigger an enquiry. HMRC cross-references the turnover and expenses on each page. If your trade A shows £20,000 turnover and £18,000 of expenses, but the expense categories clearly relate to a different type of business, HMRC will ask questions.

Another common mistake is forgetting to apportion shared costs. If you use the same vehicle for both trades, you must split the mileage and fuel costs between the two SA103 pages. Keep a mileage log showing which journeys relate to which trade.

A third issue is claiming the £1,000 trading allowance against one trade while using actual expenses for the other. The trading allowance is per person, not per trade. You can only claim it once across all your self-employment income. If you claim it, you cannot claim actual expenses for any trade. For most people with two trades, actual expenses produce a better result.

Our bookkeeping and compliance resources cover how to organise your records to avoid these issues.

Losses Across Multiple Trades

If one trade makes a loss and the other makes a profit, you can offset the loss against the profit in the same tax year. This reduces your total self-employment income and your tax bill.

For example, trade A makes £30,000 profit. Trade B makes a £8,000 loss. Your combined self-employment income is £22,000. You pay tax and NIC on £22,000, not £30,000.

If both trades make losses, you cannot offset those losses against employment income or other income in the same year (unless you meet the conditions for sideways loss relief, which is restricted). You carry the losses forward to set against future profits from the same trade.

Each trade's loss is tracked separately. Trade A's loss can only be set against future trade A profits, not trade B profits. Keep a loss memorandum for each trade in your records.

Making Tax Digital for Income Tax Self Assessment (MTD for ITSA)

From April 2026, sole traders with combined self-employment income over £50,000 must use MTD-compatible software to file quarterly updates and an end-of-year declaration. This applies to your combined turnover from all trades.

If trade A turns over £35,000 and trade B turns over £20,000, your combined £55,000 puts you inside MTD for ITSA from April 2026. If your combined turnover is between £30,000 and £50,000, you are inside from April 2027. Below £20,000, you can stay on the current annual return system for now.

MTD for ITSA requires digital record-keeping for each trade separately. You need to maintain digital records of income and expenses for trade A and trade B, then submit quarterly updates for the combined figures. Most accounting software handles this automatically once you set up separate nominal codes for each trade.

We cover this in more detail on our VAT and Making Tax Digital blog.

Practical Steps for Filing

Start by gathering your records for each trade separately. If you use accounting software, set up separate bank accounts or separate nominal codes for each trade. This makes the year-end split much cleaner.

Complete the first SA103 page for trade A using only trade A's turnover and expenses. Then complete the second SA103 page for trade B. Check that no expense is double-counted and that shared costs are apportioned fairly.

Transfer the net profit or loss from each SA103 to the SA100 main return. Add them together to get your total self-employment income. Then complete the rest of the SA100 as normal, including any other income sources.

If you are unsure about the split, ask HMRC or speak to an accountant. A badly prepared return with multiple trades is a common trigger for an HMRC enquiry. Getting it right the first time saves time and stress.

Our team at Holloway Davies are ICAEW qualified and handle multiple-trade returns regularly. You can contact us for advice specific to your situation.

Filing Deadlines and Penalties

The filing deadlines are the same regardless of how many trades you have. For the 2024/25 tax year (ending 5 April 2025), the online filing deadline is 31 January 2026. Paper returns must be filed by 31 October 2025.

Late filing penalties start at £100 if your return is up to 3 months late. After 3 months, daily penalties of £10 per day apply (up to 90 days). After 6 months, a further £300 or 5% of the tax due (whichever is higher). After 12 months, another £300 or 5%.

If you owe tax, the payment deadline is also 31 January 2026. Late payment interest is charged at the Bank of England base rate plus 2.5%.

If your combined self-employment income is over £1,000, you must file a return even if you have no tax to pay. The filing requirement is based on gross income, not profit.

This self assessment tax return guide should give you a clear path through the process. If your situation is complex, or if you are unsure about any of the allocations between trades, professional advice is money well spent.