Incorrect tax code?

billijo1

I recently got a notification from my tax service account to say there had been a change in my tax code, upon logging in I supposedly owe them money however upon checking my tax codes going back until January last year they seemed to have been changing, they are as follows Jan 2019 - March 2019 1128L, April 2019 1193L, May - October 1250L and December and January have changed to 970L 

I only have the one job, i did noticed my job that i left in December 2018 had the tax code of 1128L upon leaving in December and getting a new job in January my income went from £21000 to £25000, i then got a new job in October 2019 which my income changed to £28845. I have only ever had the one job at any given time. 

Does this make any sense to anyone and is it likely that I do owe them money or is it the other way around? 

Dazed_and_C0nfused

I have only ever had the one job at any given time. 
Does this make any sense to anyone and is it likely that I do owe them money or is it the other way around? 

Only having "one job at any given time" doesn't really matter, tax is all about what you were paid and it quite common for people who change jobs to owe tax.  

That is because they are often paid for two jobs in one tax period.  For example you might have left a job in October 2019 and been paid your final wage at the end of October and that employer would normally use your tax code and as such you would have received that months tax code allowances.

You start your new job in October and your new employer also pays you at the end of October.  So for tax purposes you have effectively had two jobs in that tax period.

Because you don't have your P45 yet from the job you just left the new employer will often use the emergency tax code and you receive a second set of tax code allowances.  As a result you have not paid sufficient tax and HMRC will adjust your tax code to get that back.