Self Assessment · Sole tradersLive — Available now

£65 per filing on Free · included in Sole trader, from £14/mo

Self Assessment for sole traders

If you're self-employed, you file an SA103S alongside your SA100 — turnover, allowable expenses and net profit. ac-co reads your bank feed and books, fills every box, shows the maths, and files direct to HMRC once you approve it.

▸ Start your return — £29 See the Self Assessment hub

HMRC-recognised · no card to start · pay only when you file

What we fill in first

Box 9Turnover

Box 20Total allowable expenses

Box 21Net profit

WHAT WE FILL IN FOR YOU

Your SA103S, box by box.

The self-employment supplementary page most sole traders need — short form (SA103S) for turnover under the VAT threshold. Every figure below is read from your connected bank and books, not typed by hand.

SA103S · Box 9

Turnover

Your business income for the year, matched from Open Banking and your bookkeeping — before any expenses come off.

SA103S · Box 10.1

Trading income allowance

Up to £1,000 you can deduct instead of your real expenses, if that leaves you better off. We work out which one wins.

Source: Tax-free allowances on property and trading income — gov.uk

SA103S · Box 20

Total allowable expenses

Stock, mileage, use of home, professional fees and the rest — categorised from your bank feed and added up automatically.

SA103S · Box 21

Net profit

Turnover minus allowable expenses — the figure Class 4 NIC and your Income Tax computation are built on.

SA103S · Box 38

CIS deductions

Work under CIS too? The 20% or 30% your contractor already withheld is claimed back here, not left sitting with HMRC.

Source: What is the Construction Industry Scheme (CIS) — gov.uk

WHAT YOU GET

Everything this return files, keeps and tells you.

Files for you

Sent to HMRC, with a receipt you keep.

SA100 with an HMRC receipt
SA103S with turnover, expenses and net profit

Keeps for you

Every box traceable to the bank line behind it.

The bank feed and books behind every box
Your SA302 calculation

Tells you

Your figure before you file, not after.

Which is bigger — the £1,000 trading allowance or your real expenses
Your estimated Income Tax and Class 4 NIC before you file

THREE THINGS PEOPLE GET WRONG

Sole trader tax return — the small print that costs money.

Default

Cash basis is the default, not accruals

Most sole traders are automatically taxed on a cash basis — money in, money out — unless they actively elect for traditional accounting. Picking the wrong one changes when income and expenses count.

Source: Simpler income tax — cash basis — gov.uk (opens in a new tab)

50%

Payments on account catch first-timers out

Once your tax bill passes a threshold, HMRC asks for two advance payments toward next year — each 50% of this year's bill — on top of what you already owe. Budget for it before January.

Source: Understand your Self Assessment tax bill — payments on account — gov.uk (opens in a new tab)

45p

Simplified expenses beat real receipts for many

A flat mileage rate for the first 10,000 business miles can be simpler — and sometimes bigger — than totting up fuel and servicing receipts. You can't mix methods for the same vehicle in the same year.

Source: Simpler income tax — simplified expenses — gov.uk (opens in a new tab)

No sign-up — try it right here

See your Income Tax and NIC estimate — no sign-up.

Enter your turnover and expenses and the same engine that drafts your SA103S gives you a labelled estimate.

Fix the figures above to see an estimate.

Estimate only — not tax advice. Figures use published HMRC rates and thresholds for the selected tax year; your actual bill depends on your full return.

An estimate from the figures you enter — your real bill comes from your filed Self Assessment return.

PRICING

One fee per return. No subscription.

Most sole traders with one business need just one supplementary page — that's the Simple tier.

50% off until 14 January 2027

Simple

One supplementary page

£29£59/ return

One business, no other income beyond PAYE or a little interest — SA100 plus your SA103S.

Start a return

Complete

Every income type

£65£129/ return

More than one income type — self-employment plus property, dividends or capital gains — every supplementary page included.

Start a return

A sole trader return, three ways.

Row	HMRC online	An accountant	ac-co
£/return	Free	£150–£400 [Sleek — accountant fees for Self Assessment, UK, 2026-09-13]	£29–£65
Hours	~4–6 hours	~1 hour, plus waiting for an appointment	~10 minutes
Drafts from your bank feed	No	If you send them	Yes
Trading allowance vs expenses worked out for you	No	Yes	Yes

Accountant fee dated 2026-09-13 — check their own quote.

OBJECTIONS

Before you file.

Do I file SA103S or SA103F as a sole trader?

SA103S (short) covers most sole traders with turnover under the VAT registration threshold and no complications like capital allowances on cars. SA103F (full) is for larger or more complex businesses. ac-co works out which one you need from your books.

What if I only started trading partway through the year?

You still file for the whole tax year, but your turnover and expenses only cover the months you traded. The SA103S has boxes for your start date, and box 9 onward only include income from that point.

Can I claim the trading allowance and expenses together?

No — you claim either the £1,000 trading allowance (box 10.1) or your actual allowable expenses (box 20), whichever is higher. You can't deduct both. ac-co calculates both and shows you which one wins.

I'm a sole trader who also works under CIS — do I file differently?

No extra form — CIS deductions your contractor already withheld go in box 38 of the same SA103S, offsetting the tax and Class 4 NIC calculated on your profit. It's one return, not two.

How much does it cost to file as a sole trader?

From £29 a return for one supplementary page — no subscription, and you only pay when you're ready to file.