You will only get backdating for the period you met the qualifying rules; so if you only met the rules, for example, two weeks before your date of claim, you will only get two weeks' extra money.
You should check your tax credits award notices carefully to make sure any backdating has been included properly.
Universal credit is being introduced geographically and in areas where the full (digital) service is available, it may no longer be possible to make a new claim for tax credits.
Existing tax credit claimants are expected to be moved across to universal credit between 20.
We will do this automatically, but we cannot go back further than 3 months, if you are a pensioner.