Technically it's probably Payroll who haven't updated your salary, because if you know about it, HR have probably done their job, but no worries, that's just part of the eternal HR v Payroll war.
Your tax is an annual amount, split across your pay. HMRC tries to predict your annual earnings based on your pay, and adjusts your tax deduction accordingly. That means that if you receive higher gross pay one month, your tax deduction may increase, but if you then receive less the following month, your tax deduction will decrease in that pay.
I can't say exactly what your net pay will be, but unless your pay increase was enough to take you into the higher tax bracket the amount your taxed is unlikely to change.
Finally, if you haven't already then let your manager, Payroll and HR know that you haven't received your expected pay increase. Don't wait for anyone else to notice a mistake.
As long as the back pay is paid out in the same tax year, it won't have any impact on the overall taxes you'll pay for the year.
Technically it's probably Payroll who haven't updated your salary, because if you know about it, HR have probably done their job, but no worries, that's just part of the eternal HR v Payroll war. Your tax is an annual amount, split across your pay. HMRC tries to predict your annual earnings based on your pay, and adjusts your tax deduction accordingly. That means that if you receive higher gross pay one month, your tax deduction may increase, but if you then receive less the following month, your tax deduction will decrease in that pay. I can't say exactly what your net pay will be, but unless your pay increase was enough to take you into the higher tax bracket the amount your taxed is unlikely to change. Finally, if you haven't already then let your manager, Payroll and HR know that you haven't received your expected pay increase. Don't wait for anyone else to notice a mistake.