Self Assessment doesn't add up?

Adrian_Harvey

Sorry everyone, rechecked my whole form and it says underpayments for previous year included, which adds up, however it still baffles me that this was not mentioned last year when I paid my outstanding balance for 2015/16.

Dazed_and_confused

Tax underpayments are often collected with a gap year in the middle.

For example if your 2016/17 underpayment could be collected through your tax code it would done via your 2018/19 tax code, starting next April. The current code for 2017/18 wouldn't be adjusted part way through the year to include a new underpayment.

So if you had an underpayment for 2014/15 it would have normally been identified in the 2015/16 tax year and then collected during 2016/17.

But inclusion in your tax code would normally mean your employer deducted extra tax.

Without more info about your tax history - have you done tax returns for a few years? What tax code was issued by HMRC for 2016/17? How was the tax code made up? What tax code did your employer use for 2016/17?