Backdated payments
[ch 3: page 28]If the Tax Credit Office receives your claim on or after 6 April 2017, they can only backdate it for up to one month. The same goes for reporting changes to your income. If you report a change that means your payments go up, the higher amount will only be backdated by up to one month. To make sure you get your higher payments backdated to the earliest possible date, you should report all changes within one month.