Royal Mail said that it selected the date following feedback from a number of its customers.
It won approval for the pricing change from postal regulator Postcomm, which told Royal Mail it could introduce it no earlier than August 17 next year, in order to allow postal users to prepare for the changes.
The company has committed to run a publicity campaign explaining the changes.
It is not allowed to make any extra overall revenue from the pricing changes, and has to balance prices rises with reductions. It has also agreed to mitigate some of the effect of price rises for business customers that spend more than £100,000 a year and find the changes add 50% or more to their postage bill.
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