The ICAEW has become aware of more errors in HMRC’s self assessment (SA) 
calculations and a number of other current SA issues.
All in all pretty disgraceful. Yet our "beloved" political elite don't give a monkey's, because they pay tax professionals to sort through this mess when submitting their returns!
Details as per the 
ICAEW:
These issues come on top of:
- A longer list of self assessment exclusions to deal with calculation issues and the first ever in-year update to SA software.
- The SA (and other) systems being unavailable between Thursday 4 and Saturday 6 January 2018. 
Error in calculation of capital gains tax affecting some trust returns
HMRC has advised us of an issue affecting a small number of 
electronically filed SA900 SA returns for trusts. HMRC’s systems are 
showing inaccurate calculations of capital gains tax in some cases. We 
have been advised that the problem has now been resolved and 
calculations shown in HMRC’s systems should now be correct for returns 
filed from 16 January 2018. HMRC will check and correct calculations for
 returns already filed.  
The 31 January payment should be based on the tax correctly calculated by commercial software.
Other errors being investigated
Members have reported some further calculation errors; these are still being investigated to check whether they are widespread.
One report concerns HMRC’s calculator not allowing the CGT annual 
exempt amount (and possibly any remaining basic rate band) to be wholly 
set against gains due at 18/28% rather than 10/20%.
Another concerns two cases where HMRC adjustments for marriage 
allowance reduced the liability in one case to zero and in another case 
to the previous value for payments on account.
HMRC pre-population service within third party software unavailable
Agents are currently unable to use the HMRC pre-population service 
(for employment data) within third party software. The service was 
disabled on 16 January 2018 while the problem is investigated.
SA statements missing and delayed
ICAEW has received many reports of statements not arriving. HMRC has 
confirmed that SA statements are being issued between 31 December 2017 
and 8 January 2018 so clients may not receive them until the third week 
of January. HMRC has advised that paper SA statements will be issued 
before the due date for payment where returns were filed by 8 January 
2018.
Payments on account not showing on statements
There has been a recurrence of the issue where payments on account 
(for 2017/18) do not appear on statements (paper and online). HMRC 
introduced a fix to correct this issue in December 2017 but it seems 
that this fix may have missed some cases.
It may be appropriate to advise clients who rely on HMRC statements 
to check that the payment on account due on 31 January 2018 is included 
in the sum they expect to pay.
Give us your feedback
It is extremely concerning that there are so many issues with HMRC’s 
SA software this year. ICAEW will pursue this poor service with HMRC. In
 the meantime we suggest that agents check calculations very carefully. 
Tax does have to be taxing.
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