Self-assessment says I've underpaid tax. Don't understand why

chrisbur

The OP asked a while back
" I would just like to understand how it's possible for me to have underpaid tax by £1000."

If we assume a wage of £60000 (5000 a month)  which is paid by both an old employer and a new employer for month 12 (a payment made anytime from 6/3 to 5/4 ) tax code of 1257L used by old employer and new employer uses emergency tax code.
Old employer will have paid £60000 by month 12 from which £11428 tax will have been deducted
New employer uses E tax 1257L non cumulative to pay £5000 from which £ 952.06 is deducted.
If the 60000 and 5000 had been paid together in month 12 then for £65000 you get tax due of £11428

An under payment of £1047.94
HMRC will not come to exactly the same answer as they do not use the PAYE system.
Figures can be checked here
http://payecalculator.hmrc.gov.uk/PAYE0.aspx
This uses this year's  figures but there was no change.

Actual earnings are not going to change things unless they cause a change in tax bands as the tax owed is due to extra tax free allowance and extra 20% tax band allowance. Different tax codes would alter the figures.

Strummer22

Are you repaying student loan? If so, have you switched to paying by direct debit rather than via your employer? 

This is my situation and I did my first self-assessment for tax year 2021-22 and had a nasty shock when I said I'd underpaid by over £1,000. The self-assessment form asks questions in a confusing way:

"If you've received notification from the Student Loans Company that your repayment of an Income Contingent Loan was due before 6 April 2022" - well yes, I've been paying my loan back since 2009.

"If your employer has deducted Student Loan repayments enter the amount deducted" - zero, I'm paying the last couple of thousand by direct debit.

HMRC then think I owe loads of student loan money. I just re-did the return but said no to the first question above.

This may not be the issue you're having but might help someone else.