Help Centre · Self Assessment (Beta) · 2 min read

The tax calculation and the SA302 PDF

The live SA302-style calculation: the staged statement, the band-by-band breakdown, informational versus blocking warnings, and the downloadable SA302 PDF for lenders.

Tax Optimiser Updated 3 Jul 2026
Beta feature — Self Assessment tax returns are currently in beta and are switched on for one accountant firm at a time. To gain access for your firm, email support@taxoptimiser.co.uk and the team will enable it and help you get started.

Because the traditional Self Assessment channel has no HMRC calculation service, Tax Optimiser computes the full tax position itself — recalculated on every save, so the Calculation (SA302) section and the Total Tax Due card are never stale.

Reading the calculation

The Calculation section: income by type with box references, allowances, Income Tax, Class 4 NIC, student loan, tax deducted, the balancing payment and payments on account

The statement follows the same staged shape as HMRC’s SA302: income by type, deductions and the Personal Allowance (with the £100,000 taper where it applies), Income Tax, Class 4 and Class 2 National Insurance, student loan repayments, tax already deducted at source (PAYE, CIS, taxed interest), and finally the balancing payment and any payments on account for the following year with their due dates.

How the tax was worked out

Below the statement, the band breakdown shows every slice of income against the band and rate that taxed it — including the 0% slices (Personal Savings Allowance, dividend allowance, savings starting rate) and any band extension from Gift Aid or pension contributions. Scottish taxpayers see the Scottish bands on non-savings income, with savings and dividends staying on UK-wide bands, exactly as HMRC applies them.

The band breakdown: non-savings income at basic and higher rate, the Personal Savings Allowance and dividend allowance at 0%, and dividends at the higher dividend rate

Warnings: informational and blocking

The calculation flags anything it wants you to know about. Informational notes explain a treatment (for example how a state pension lump sum was taxed). Blocking warnings, shown in red, mean the return cannot be filed online through Tax Optimiser — typically because it needs a page the beta does not yet support. A blocked return fails the pre-flight checks on the Submission screen, so nothing incomplete can reach HMRC by accident.

The SA302 PDF

Download SA302 PDF produces the tax-calculation document clients are asked for by mortgage lenders: the full statement, the band breakdown and the payments on account, over the client’s name and UTR. The PDF is recalculated from the saved figures at the moment you download it, and carries a draft banner until HMRC has accepted the return. As with any software calculation, it is advisory until HMRC processes the return — HMRC’s own figure is definitive.

Next: Submitting the return to HMRC.

The short version

The tax calculation and the SA302 PDF — in brief

The calculation re-runs on every save; the statement follows HMRC's SA302 stages down to the balancing payment and payments on account.

The band breakdown shows every slice of income against its band and rate, including 0% allowance slices and Gift Aid band extensions; Scottish bands apply to non-savings income only.

Blocking warnings (red) stop online filing and fail the pre-flight checks; informational notes just explain a treatment.

Download SA302 PDF produces the lender-ready calculation document, recalculated at download time, with a draft banner until HMRC accepts the return.