Corrections
Corrections to the calculation
A correction is added here whenever a fix to the calculation could change a figure somebody has already put on a return. Each one says what was wrong, who could be affected, which figure could be wrong and in which direction, the largest effect seen on invented test cases, and what in your own working tells you whether it reached you.
Nothing here is a message about your tax. These are facts about the software. HMRC explains how a person changes a Self Assessment return they have already sent, and by when, at gov.uk/self-assessment-tax-returns/corrections — in outline, a return can be changed within 12 months of the filing deadline for that year, and after that by writing to HMRC. That is a government service and the description of it is HMRC's, not ours.
Every figure this app produces carries the exact version of the calculation that made it, in the working in your pack. The machine-readable copy of this page carries the same versions, so the app will in time be able to make the comparison for you.
The blind person's allowance for 2026-27 was carried forward from 2025-26 instead of taking the published figure
- Who this could affect
- A blind taxpayer, on a 2026-27 calculation. Nothing in the app asks whether a person claims this allowance and nothing sets it, so no figure the app has produced has used it.
- Which figure
- The blind person's allowance, and so income tax on the main return (SA100). A figure that can go on a return.
- Which way it was wrong
- Too high. The allowance was £3,130 where £3,250 is published for 2026-27, so £120 less was set against income.
- The largest effect on invented test cases
- £120 of allowance, which is £54 of tax at the additional rate.
- What tells you whether it reached you
- A 2026-27 pack that shows a blind person's allowance of £3,130. No pack the app has produced shows one at all.
- Fixed in
c036e15c2232— The blind person's allowance was never frozen, so it cannot be copied forward
Income tax was rounded once on the total rather than on each band as it was charged
- Who this could affect
- Everyone. It bites where income has pence in it and crosses a band, and hardest where there is a savings or dividend slice.
- Which figure
- Income tax on the main return (SA100), and everything worked out from it — the balance owed, and the total tax and National Insurance the pension figures are built on. A figure that can go on a return.
- Which way it was wrong
- Too high by one penny. HMRC's own calculation specification truncates each band as it is charged, which can only ever go one way.
- The largest effect on invented test cases
- One penny. It moved eleven of the twenty-five pinned test cases; the largest figure it moved was £70,094.51, where £70,094.50 is due.
- What tells you whether it reached you
- Add up the band rows printed in the working. If they do not add to the total printed under them, the pack was produced before this was fixed and the total is a penny high.
- Fixed in
72057a4f76a5— One rounding, where HMRC puts it: on each band, not on the total
A day's trades in a foreign currency were converted to sterling one fill at a time
- Who this could affect
- Anyone who sold or bought shares in a currency other than sterling — in practice a US broker — on a day the order was filled in more than one piece.
- Which figure
- The proceeds and the gain on the capital gains pages (SA108). A figure that can go on a return.
- Which way it was wrong
- Either way, by a rounding of up to one penny for each extra fill on the day.
- The largest effect on invented test cases
- Up to one penny for each fill after the first. On an invented case a day split into ten fills gave proceeds of £1,026.53 where £1,026.54 is right. Where the pence straddle a pound it can move a whole-pound box by £1.
- What tells you whether it reached you
- Each part of a disposal now carries the amount in the currency it was traded in as well as in sterling. A pack without those per-part currency amounts was produced before this was fixed, and only a day with more than one fill was affected.
- Fixed in
9a6d80a45858— One transaction, one consideration, one conversion
National Insurance for 2023-24 was charged at one of the year's two rates for the whole year
- Who this could affect
- Anyone whose National Insurance was worked out on a whole-year basis for 2023-24 — which is how the pension figures price a change to salary sacrifice. Categories C, J and Z were not affected.
- Which figure
- The employee National Insurance figure in the working and in the pension figures. Class 1 National Insurance is not a box on a Self Assessment return, so this is not by itself a figure that was filed. A figure in the working, not a box on a return.
- Which way it was wrong
- Too low. The main rate was 12% to 5 January 2024 and 10% from 6 January 2024; the blended annual rate is 11.5%.
- The largest effect on invented test cases
- £565.50 at any income at or above £50,270, and proportionally less below it. £3,770.00 was shown where £4,335.50 is due.
- What tells you whether it reached you
- Only a 2023-24 year, and only where National Insurance was taken for the year as a whole rather than pay period by pay period.
- Fixed in
0ad98ab8f5f7— A year that changed its NI rate in January did not charge either rate for all of it
The High Income Child Benefit Charge was worked out as a percentage of the child benefit with its pence still on
- Who this could affect
- Anyone receiving child benefit whose income put them in the band where the charge is tapered rather than at the full amount. The weekly rates of child benefit always have pence in them, so it applied to everyone in that band.
- Which figure
- The High Income Child Benefit Charge on the main return (SA100). A figure that can go on a return.
- Which way it was wrong
- Too high. Section 681C(3) of the Income Tax (Earnings and Pensions) Act 2003 rounds down three times; the app rounded down twice.
- The largest effect on invented test cases
- £1. On an invented case with adjusted net income of £75,200 in 2024-25 and child benefit of £1,772.84, the charge came out at £1,347 where £1,346 is due.
- What tells you whether it reached you
- The working now shows the whole-pound child benefit total the percentage was taken of. A pack that shows a charge but no such total was produced before this was fixed.
- Fixed in
9ee7ccc25dc7— The child benefit charge is a percentage of whole pounds, not of the pence
The movement in the exchange rate between a sale and the conversion to sterling was described as a gain or loss on the dollars
- Who this could affect
- Anyone who sold shares in dollars and held the dollars in the brokerage account before converting them to sterling.
- Which figure
- Chargeable gains on the capital gains pages (SA108). A figure that can go on a return.
- Which way it was wrong
- Either way. For an individual, foreign currency in a bank or brokerage account is not a chargeable asset (Taxation of Chargeable Gains Act 1992 sections 251(1) and 252). Where the dollar fell between the sale and the conversion, the app described an allowable loss that does not exist; where it rose, a gain that does not exist.
- The largest effect on invented test cases
- There is no ceiling to quote: it is the movement in the exchange rate on that person's own sale proceeds.
- What tells you whether it reached you
- The sentence printed above the table of sterling received. A pack that calls the difference a gain or a loss on the dollars themselves, citing CG78300, was produced before this was fixed.
- Fixed in
b1133f93e938— Dollars in a brokerage account are not a chargeable asset, and the app said they were
A sale inside a stocks and shares ISA was taxed as though it were a taxable account
- Who this could affect
- Anyone with a stocks and shares ISA at a platform that issues the same kind of contract note for every account it holds for a person. Hargreaves Lansdown, Interactive Investor and AJ Bell all do.
- Which figure
- Chargeable gains on the capital gains pages (SA108). A figure that can go on a return.
- Which way it was wrong
- Too high. A gain that is not taxable was added to the taxable ones.
- The largest effect on invented test cases
- There is no ceiling to quote: it is the whole gain on the ISA sale.
- What tells you whether it reached you
- Every disposal in the working now names the account it was made in and says whether it is taxable or tax free. A pack whose disposals do not name an account was produced before this was fixed.
- Fixed in
64854adc4523— Which account a sale was made in, and losses that remember which year they are from
A capital loss from an earlier year could not be entered, and a loss for a later year was worked out and then dropped
- Who this could affect
- Anyone who has ever sold shares at a loss. In a browser there was no way to enter a loss from an earlier year at all.
- Which figure
- Chargeable gains on the capital gains pages (SA108), in the year the loss should have been set against gains and again in the year after. A figure that can go on a return.
- Which way it was wrong
- Too high, by the amount of the loss that could not be used.
- The largest effect on invented test cases
- There is no ceiling to quote: it is the size of the loss.
- What tells you whether it reached you
- The working now carries a record of losses with the year each one arose and the date by which a claim for it has to be made. A pack with no such record was produced before this was fixed.
- Fixed in
64854adc4523— Which account a sale was made in, and losses that remember which year they are from
Three rules in the app's re-run of PAYE did not match HMRC's own specification
- Who this could affect
- Anyone on an ordinary tax code above 500, which is most people — 1257L is one. And anyone on a BR, D0, D1 or NT code, above all where the code changed to BR or NT part-way through a year.
- Which figure
- The app's own re-run of the PAYE an employer operated, and the difference it reports beside the tax deducted. The tax deducted on the employment pages (SA102 box 2) is copied from the P60 or the payslips and not from this re-run, so no figure on a return was worked out from it. A figure in the working, not a box on a return.
- Which way it was wrong
- Either way. The free-pay rule was a penny a month low; a flat code was charged period by period where it should be cumulative, which on a code that changed mid-year meant no refund was shown at all.
- The largest effect on invented test cases
- On an ordinary code, up to 45p between two adjacent pay periods, netting to nil over the year. On a flat code that changed part-way through a year it is not small: on HMRC's own test data a month carrying a £29,406.05 refund was shown as £2,518.00 deducted.
- What tells you whether it reached you
- A PAYE recheck line reporting a difference of a few pence on an ordinary code, or any difference at all in a year where the tax code changed to BR or NT.
- Fixed in
0b2dd8a7cccf— Three rules HMRC's own specifications state and the engine had wrong
A Scottish taxpayer's annual allowance charge was worked out at rest-of-UK rates
- Who this could affect
- A Scottish taxpayer who put more into a pension in a year than the annual allowance allowed, after using up any unused allowance from the three earlier years.
- Which figure
- The annual allowance charge in the pension figures — the figure HMRC's HS345 working sheet produces for the additional information pages (SA101). A figure that can go on a return.
- Which way it was wrong
- Too low. The charge is sliced over the taxpayer's own band table, and Scotland's has five or six bands where the rest of the UK has three.
- The largest effect on invented test cases
- On a hand-worked case, £10,000 of excess on £100,000 of taxable income is £4,500 in Scotland and £4,000 elsewhere: £500.
- What tells you whether it reached you
- A pack for a Scottish taxpayer showing an annual allowance charge with no Scottish band table under it was produced before this was fixed.
- Fixed in
9fbf6aa6955f— A tapered prior year, a Scottish charge, and a defined-benefit accrual the taper never saw
The Scottish top rate started £12,570 too early for a taxpayer past the £100,000 allowance taper
- Who this could affect
- A Scottish taxpayer with income over about £100,000, where the personal allowance is being tapered away. Nobody below the taper was affected.
- Which figure
- The income tax figure in the pension figures and in the app's re-run of the PAYE your employer operated. Scottish income tax is not worked out for the return itself — that is on the standing list of what this app does not do — so no box on a return carried this. A figure in the working, not a box on a return.
- Which way it was wrong
- Too high. £12,570 of income was charged at the top rate that belongs at the advanced rate.
- The largest effect on invented test cases
- £377.10 on an invented 2025-26 case with employment income of £130,000, and £628.50 in 2023-24, where the step between the two rates is larger.
- What tells you whether it reached you
- A pack for a Scottish taxpayer with income over £100,000 whose band table ends its last finite band at £112,570 rather than at £125,140.
- Fixed in
a4c3ece4fdbf— A Scottish taxpayer past the £100,000 taper was charged 48% on £12,570 that belongs at 45%
How an entry gets here
Any change to a rule that can move a figure somebody could have filed gets an entry, on
the day it is merged, whether or not anyone is known to have been affected. That rule is
written down in docs/corrections.md and in the checklist every change to
this app is reviewed against, so it is not left to whoever happens to be looking.
People who signed up for a beta pass are emailed when an entry is added that could affect them. That is a service message about software they hold a pass for, not marketing: nothing is sold in it and nothing else is put in it.