When does the £1,000 trading allowance beat actual expenses?

Strictly whenever actual business expenses are below £1,000. Below that threshold the £1,000 flat deduction is straightforwardly better. The engine compares the two paths and picks whichever produces lower taxable profits.

Is voluntary Class 2 worth £179.40/yr?

Usually yes. Class 2 voluntary contributions cost £3.45/wk (£179.40/yr) and buy a State Pension qualifying year. The Full New State Pension is £230.25/wk (£11,973/yr) and needs 35 qualifying years. One year of voluntary Class 2 buys roughly £342 of annual State Pension at retirement — a payback period of about 6 months on first claim.

At what profit level should I incorporate?

Pure-tax break-even is usually between £30k and £50k of profit, depending on expenses and other income. The calculator bisects for the exact number. Note that Ltd Co adds ~£800–£1,500/yr of accountancy / filing overhead which a sole trader does not pay — net the tax gain against that before incorporating.

Why does the income tax figure not match HMRC's calculation if I have other income?

It does — the engine computes income tax on the total of (taxable profits + other income), then pro-rates the share attributable to the self-employment by the income ratio. HMRC does it on the same total but reports a single tax figure; this calculator shows the sole-trader share specifically so the comparison with the Ltd Co route is apples-to-apples.

Are student loan repayments included?

No. Student Loan repayments (Plan 1 / 2 / 4 / 5 / Postgraduate) are not modelled. Plan 2 at 9% above £27,295 would add roughly 9p of marginal cost to each £1 of taxable income above the threshold — add to the marginal rate shown if you have an outstanding loan.

No. Mandatory VAT registration kicks in once taxable turnover crosses £90,000 in any rolling 12-month period. Below that it is voluntary. The income-tax / NI math on this calculator is unaffected by VAT registration.

UK Tax Year 2026/27 · Self-Employed (rUK)

Sole Trader Tax

Computes income tax, Class 4 NI and optional Class 2 voluntary contributions for the 2026/27 tax year. Automates the £1,000 trading allowance vs actual expenses decision. Built-in Ltd Co incorporation break-even — at what profit level should you incorporate? — by bisection.

Inputs

Annual turnover (£)Total gross income from the self-employment activity for the 2026/27 tax year.Actual business expenses (£/yr)Wholly-and-exclusively business costs. The engine compares this against the £1,000 trading allowance and picks the better of the two.Other personal income (£/yr)PAYE salary, rental, pensions etc. Stacks below the self-employment profits in the band schedule.AgeUsed in the Ltd-Co comparison branch for Annual Allowance / taper considerations.Pay voluntary Class 2 NI (£179.40/yr)Buys a State Pension qualifying year. Strongly recommended if profits are below the Small Profits Threshold (£6,725 for 2026/27) and the NI record has gaps.Show Ltd-Co incorporation comparisonDrives the optimiser at the same turnover and expense pot (no pension), then bisects for the break-even profit level.

Net take-home — sole trader route

Net cash

£34,539

Effective rate

17.7%

Taxable profits (after expenses / allowance)	£42,500
Trading allowance applied?	No (actual expenses larger)
Income tax (sole-trader share)	£5,986
Class 4 NI	£1,796
Class 2 NI (voluntary)	£179
Marginal rate on next £1 of profit	26%

Should I incorporate?

Same turnover and expense pot, run through the Ltd Co joint optimiser (no pension contribution, cash optimum). Apples-to-apples with the sole-trader figure above.

Sole trader net cash	£34,539
Ltd Co net cash (cash optimum)	£33,896
Gap	£642 for staying sole trader
Break-even turnover (by bisection)	No sign-change in [£15k, £400k] range

Caveat: this is a pure-tax comparison. A Ltd Co adds ~£800–£1,500/yr of accountancy / filing overhead, plus the loss of the £1,000 trading allowance and public Companies House filings. Net the gap against those non-tax frictions before incorporating.

The trading-allowance choice in one paragraph

The £1,000 trading allowance under ITTOIA 2005 s.783A is a flat deduction available in lieu of claiming actual expenses. It strictly beats actual expenses whenever actual expenses are below £1,000. The engine compares the two paths and applies the lower-tax option — so if you have £300 of actual costs but enter them as £300, the calculator silently switches to the trading allowance and saves you (£1,000 − £300) × marginal rate in tax. The recommendation appears in the notes panel.

The Class 4 NI band schedule

For 2026/27: 6% on profits between the Lower Profits Limit (£12,570) and the Upper Profits Limit (£50,270), then 2% on profits above £50,270 (HMRC NIM24001). Class 2 is no longer compulsory above the Small Profits Threshold but remains payable on a voluntary basis at £3.45/wk (£179.40/yr) to maintain a State Pension qualifying year.

Why "should I incorporate?" is a bisection problem

The function f(t) = ltdCoNetCash(t) − soleTraderNetCash(t) is the gap in £/yr of net cash between operating as a Ltd Co director (running the full salary–dividend–pension optimiser) and operating as a sole trader (income tax + Class 4 NI on profits), at turnover t. At very low turnover the gap is small or negative (sole-trader simplicity dominates); at high turnover the gap is materially positive (Ltd Co dividend-band machinery dominates). The break-even is the turnover at which the gap is zero. The calculator bisects on the £15k–£400k range with 35 iterations — accurate to within roughly £100 of net cash.

For the same engine driven across 200+ profession × income × structure combinations, see the programmatic /pay pages.

What this calculator does not model

Student loan repayments (Plan 1 / 2 / 4 / 5 / Postgraduate).
The High Income Child Benefit Charge (HICBC).
VAT (mandatory above £90,000 of taxable turnover from 1 April 2024).
Scottish income-tax bands.
Capital allowances on plant / machinery / vehicles — the engine treats them as part of "actual expenses".

The full conventions / methodology / source citations for the BracketMath engines are at /about. The disclaimer for all BracketMath outputs is at /disclaimer.